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Following on from this question: How many humans have been in my lineage? Is it almost the same for every human currently living?
How many generations back do my ancestors go? Not just human ancestors, but all ancestors, right back to the first lifeform.
I recognise that there are some impossible unknowns here, so I'm looking for some kind of Fermi estimate.
Who Counts as Family in a Family Tree? Who to Add and Who to Leave Out
The term family tree is defined as “a diagram showing the relationships between people in several generations of a family.” Add your parents, grandparents and great grandparents and you’re well on your way to building your own tree.
But, as we all know, family is an incredibly complex concept with biological, legal, social and emotional elements. And, for this reason, the question of who counts as family in a family tree is far from simple.
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In our daily lives, family often has less to do with biological or legal connections and more to do with personal relationships. Those people who are intimate parts of our lives, who we love and care for, who care for us, are our family. What makes a mother, father, sibling, child, grandchild is seldom straightforward.
But in a genealogical sense people often get muddled and are unsure who should be added to their family tree. Adoptions, step-parent relationships, unmarried partners, multiple marriages, the discovery that a parent or sibling is not related biologically – all of these scenarios may cause some serious head scratching.
And even if we don’t experience any of these instances in our immediate lives, most of us will encounter them as we dig deeper into our family’s past, leading us to ask:
“What constitutes family in a family tree?”
“Who should I add and who should I leave out?”
To answer these questions we have to ask ourselves another, “What is the purpose of a family tree?” Is it to lay out a biological map of our past, or to tell as accurate a story as possible about the lives of our ancestors?
There are very few who would argue that the purpose of genealogy is to simply understand the biological connections of humans. After all, family history researchers spend much of their time digging through old records and histories – social documents – trying to better understand the realities of those they are researching. This work makes it incredibly apparent that family is much more complex than a bloodline.
Yet most of us feel a need to create a tree that tells a biological story – a physical record of what we are made of in an attempt to understand our ancestors and ourselves.
But if family is more than biology, and it is family that shapes us, than shouldn’t our trees be more than biological record books? If we create a tree that reflects only physical relationships are we really building an accurate picture of our ancestors’ lives?
If we want to develop a full and accurate picture of our family’s past we need to document everything we can about the lives that created it – and that includes taking the time to discover and include non biological relationships. We need to tell the very complex story that is family, generation after generation, if we want to understand where we come from.
In a previous article we discussed the importance of adding non direct-line relatives to a family tree – such as aunts, uncles and cousins – to form a well-rounded family history. And this scenario is no different. Our trees should be filled with those people that our ancestors considered family – no matter their biological or legal relationship.
A first marriage of great grandmother Jeanie for instance – even if it didn’t produce any children – had a huge impact on her life, as did the unofficial stepfather of your grandfather. He may not be biologically or legally related but he surely influenced the kind of man your grandfather became and the lessons he passed on to you.
And adding these relationships to your tree will help you uncover new records about your family’s past as you branch out and create new pathways for discovery.
Of course, only you can decide who should appear in your own family tree – but when you do you should always take the time to properly document the relationships so that others know exactly what they are looking at.
A stepmother for instance, even if she is the only listed mother, should be labeled as such. This will ensure that future generations will have an accurate view of the past and other family historians will have the details they need to build on your research.
Almost every family tree program makes adding multiple spouses to a person and non biological relationships for a child possible. Look in the help documentation in whatever program you are using for help.
Here is a quick walk through for how to edit relationships and add more that one partner/spouse on Ancestry. Links to how to edit relationships on MyHeritage and RootsFinder are found below.
To edit relationships in an Ancestry tree simply view the profile of one of the people in the relationship. Now click on the Edit button in the upper right hand corner of the page and select Edit Relationships.
Once on the Edit Relationships screen you will see that each person has a dropdown box of relationship possibilities. Click on the box and select an option.
For a parent or child you can choose:
For a spouse/partner you have the option of:
On this screen you can also add additional partners and children quite easily, including adding a child from another marriage/relationship. To do this simply add a child and choose from parental options at the bottom of the screen.
- MyHeritage has several articles relating to this topic – including adding adopted children and partners – in their help center.
- RootsFinder information on editing relationships is here. Read our intro and how-to on using their free online tree here.
By Melanie Mayo-Laakso, Family History Daily Editor
Image: “Family of J. J. Moore. All but mother and two smallest children on steps work in Washington Cotton Mills, Fries Va. Smallest spinner (right hand end of front row) said she was 14, but she surely is not. The family came from a Carolina farm three years ago. Location: Fries, Virginia.” May, 1911. Library of Congress.
8 thoughts on &ldquoWho Counts as Family in a Family Tree? Who to Add and Who to Leave Out&rdquo
I want to know what gives you the right to send my EX-HUSBAND all my personal family history. I am sick of him sending me things like a picture of my Grandparents graves, etc.. It is none of his business who is on my family tree!
It is very intrusive to me and I am trying to find out if it is even legal!
Please respect the request of relatives to be left off to protect their privacy. I for one do not want my name and especially dob on anyone’s family tree.
In my experience living persons are marked as private listing no name – date of birth or any other info
List as much information as possible. Step’s, half’s, spouses and their families if discovered labeling with relationship. This practice has led me to “find” much information. Including, 2 boys and 1girl the boys couldn’t be located when grandpa’s will was probated in the 1890’s.
The practice has also led to many discoveries I have found no where else.
My advice is “always include” …you never know what discoveries the information will lead you to down the road.
We have many loving men in our family who have raised other mens’ children. This question came up every so often, especially as my husband adopted my children, and raised them from ages 1 and 4. I talked about their father in everyday conversations, both good and bad things, but after we split he stayed away so as not to confuse them.
My children know their blood relatives, but have a closer relation with hubby’s family.
We came up with this simple little rule that so far seems to make everyone happy:
List the stepfather as “step” or “adoptive” or whatever, right along with the “bio” father. Do a full profile on both fathers. Both are important, as stated above.
Then think about your relationships with stepfather’s family, being sure to ask the children involved the tree is, after all, for them. Decide which step relatives have close relationships with your children: do they see each other at Thanksgiving, go on vacation together, friends on facebook, and so on. If the step relative is known, include them. If not, leave them off. They have their own tree if you want to look for further information. So on our tree, we included stepfather’s siblings and their families, parents, grandmothers and a few of his aunts and uncles. Each case is different, but the rule’s always the same, and it seem to cover what’s important.
I don’t add parents of a uncle/aunt by marriage because you are researching a whole different family then. I add all husbands, wives, children & stepchildren, but I only add siblings of my biological line & their spouses, children. It’s confusing enough without going off in other directions! One dna match of mine was adding the grandfather of his brothers wife!
In this case I list the parents under the birth notation giving their life span if available. ei Parents John William Jones [1891-1950] + Alice Smith [1895-1945]. Also note especially in small communities more than one offspring of the above parents could have married into the same blood-line.
It’s the old nurture or nature question that constantly comes up in psychology. It is all part of our story. For me, I’d rather study the complex, nuanced reality, than only consider the clinically biological.
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Evolutionary psychology is an approach that views human nature as the product of a universal set of evolved psychological adaptations to recurring problems in the ancestral environment. Proponents suggest that it seeks to integrate psychology into the other natural sciences, rooting it in the organizing theory of biology (evolutionary theory), and thus understanding psychology as a branch of biology. Anthropologist John Tooby and psychologist Leda Cosmides note:
Evolutionary psychology is the long-forestalled scientific attempt to assemble out of the disjointed, fragmentary, and mutually contradictory human disciplines a single, logically integrated research framework for the psychological, social, and behavioral sciences – a framework that not only incorporates the evolutionary sciences on a full and equal basis, but that systematically works out all of the revisions in existing belief and research practice that such a synthesis requires. 
Just as human physiology and evolutionary physiology have worked to identify physical adaptations of the body that represent "human physiological nature," the purpose of evolutionary psychology is to identify evolved emotional and cognitive adaptations that represent "human psychological nature." According to Steven Pinker, it is "not a single theory but a large set of hypotheses" and a term that "has also come to refer to a particular way of applying evolutionary theory to the mind, with an emphasis on adaptation, gene-level selection, and modularity." Evolutionary psychology adopts an understanding of the mind that is based on the computational theory of mind. It describes mental processes as computational operations, so that, for example, a fear response is described as arising from a neurological computation that inputs the perceptional data, e.g. a visual image of a spider, and outputs the appropriate reaction, e.g. fear of possibly dangerous animals. Under this view, any domain-general learning is impossible because of the combinatorial explosion. Evolutionary Psychology specifies the domain as the problems of survival and reproduction. 
While philosophers have generally considered the human mind to include broad faculties, such as reason and lust, evolutionary psychologists describe evolved psychological mechanisms as narrowly focused to deal with specific issues, such as catching cheaters or choosing mates. The discipline views the human brain as comprising many functional mechanisms  called psychological adaptations or evolved cognitive mechanisms or cognitive modules, designed by the process of natural selection. Examples include language-acquisition modules, incest-avoidance mechanisms, cheater-detection mechanisms, intelligence and sex-specific mating preferences, foraging mechanisms, alliance-tracking mechanisms, agent-detection mechanisms, and others. Some mechanisms, termed domain-specific, deal with recurrent adaptive problems over the course of human evolutionary history. Domain-general mechanisms, on the other hand, are proposed to deal with evolutionary novelty. 
Evolutionary psychology has roots in cognitive psychology and evolutionary biology but also draws on behavioral ecology, artificial intelligence, genetics, ethology, anthropology, archaeology, biology, and zoology. It is closely linked to sociobiology,  but there are key differences between them including the emphasis on domain-specific rather than domain-general mechanisms, the relevance of measures of current fitness, the importance of mismatch theory, and psychology rather than behavior.
Nikolaas Tinbergen's four categories of questions can help to clarify the distinctions between several different, but complementary, types of explanations.  Evolutionary psychology focuses primarily on the "why?" questions, while traditional psychology focuses on the "how?" questions. 
|Sequential vs. Static Perspective|
Explanation of current form in terms of a historical sequence
Explanation of the current form of species
|How vs. Why Questions||Proximate |
How an individual organism's structures function
Developmental explanations for changes in individuals, from DNA to their current form
Mechanistic explanations for how an organism's structures work
Why a species evolved the structures (adaptations) it has
The history of the evolution of sequential changes in a species over many generations
A species trait that evolved to solve a reproductive or survival problem in the ancestral environment
Evolutionary psychology is founded on several core premises.
- The brain is an information processing device, and it produces behavior in response to external and internal inputs. 
- The brain's adaptive mechanisms were shaped by natural and sexual selection. 
- Different neural mechanisms are specialized for solving problems in humanity's evolutionary past. 
- The brain has evolved specialized neural mechanisms that were designed for solving problems that recurred over deep evolutionary time,  giving modern humans stone-age minds. 
- Most contents and processes of the brain are unconscious and most mental problems that seem easy to solve are actually extremely difficult problems that are solved unconsciously by complicated neural mechanisms. 
- Human psychology consists of many specialized mechanisms, each sensitive to different classes of information or inputs. These mechanisms combine to produce manifest behavior. 
Evolutionary psychology has its historical roots in Charles Darwin's theory of natural selection.  In The Origin of Species, Darwin predicted that psychology would develop an evolutionary basis:
In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation.
Two of his later books were devoted to the study of animal emotions and psychology The Descent of Man, and Selection in Relation to Sex in 1871 and The Expression of the Emotions in Man and Animals in 1872. Darwin's work inspired William James's functionalist approach to psychology.  Darwin's theories of evolution, adaptation, and natural selection have provided insight into why brains function the way they do.  
The content of evolutionary psychology has derived from, on the one hand, the biological sciences (especially evolutionary theory as it relates to ancient human environments, the study of paleoanthropology and animal behavior) and, on the other, the human sciences, especially psychology.
Evolutionary biology as an academic discipline emerged with the modern synthesis in the 1930s and 1940s.  In the 1930s the study of animal behavior (ethology) emerged with the work of the Dutch biologist Nikolaas Tinbergen and the Austrian biologists Konrad Lorenz and Karl von Frisch.
W.D. Hamilton's (1964) papers on inclusive fitness and Robert Trivers's (1972)  theories on reciprocity and parental investment helped to establish evolutionary thinking in psychology and the other social sciences. In 1975, Edward O. Wilson combined evolutionary theory with studies of animal and social behavior, building on the works of Lorenz and Tinbergen, in his book Sociobiology: The New Synthesis.
In the 1970s, two major branches developed from ethology. Firstly, the study of animal social behavior (including humans) generated sociobiology, defined by its pre-eminent proponent Edward O. Wilson in 1975 as "the systematic study of the biological basis of all social behavior"  and in 1978 as "the extension of population biology and evolutionary theory to social organization."  Secondly, there was behavioral ecology which placed less emphasis on social behavior it focused on the ecological and evolutionary basis of animal and human behavior.
In the 1970s and 1980s university departments began to include the term evolutionary biology in their titles. The modern era of evolutionary psychology was ushered in, in particular, by Donald Symons' 1979 book The Evolution of Human Sexuality and Leda Cosmides and John Tooby's 1992 book The Adapted Mind.  David Buller observed that the term "evolutionary psychology" is sometimes seen as denoting research based on the specific methodological and theoretical commitments of certain researchers from the Santa Barbara school (University of California), thus some evolutionary psychologists prefer to term their work "human ecology", "human behavioural ecology" or "evolutionary anthropology" instead. 
From psychology there are the primary streams of developmental, social and cognitive psychology. Establishing some measure of the relative influence of genetics and environment on behavior has been at the core of behavioral genetics and its variants, notably studies at the molecular level that examine the relationship between genes, neurotransmitters and behavior. Dual inheritance theory (DIT), developed in the late 1970s and early 1980s, has a slightly different perspective by trying to explain how human behavior is a product of two different and interacting evolutionary processes: genetic evolution and cultural evolution. DIT is seen by some as a "middle-ground" between views that emphasize human universals versus those that emphasize cultural variation. 
The theories on which evolutionary psychology is based originated with Charles Darwin's work, including his speculations about the evolutionary origins of social instincts in humans. Modern evolutionary psychology, however, is possible only because of advances in evolutionary theory in the 20th century.
Evolutionary psychologists say that natural selection has provided humans with many psychological adaptations, in much the same way that it generated humans' anatomical and physiological adaptations.  As with adaptations in general, psychological adaptations are said to be specialized for the environment in which an organism evolved, the environment of evolutionary adaptedness.   Sexual selection provides organisms with adaptations related to mating.  For male mammals, which have a relatively high maximal potential reproduction rate, sexual selection leads to adaptations that help them compete for females.  For female mammals, with a relatively low maximal potential reproduction rate, sexual selection leads to choosiness, which helps females select higher quality mates.  Charles Darwin described both natural selection and sexual selection, and he relied on group selection to explain the evolution of altruistic (self-sacrificing) behavior. But group selection was considered a weak explanation, because in any group the less altruistic individuals will be more likely to survive, and the group will become less self-sacrificing as a whole.
In 1964, William D. Hamilton proposed inclusive fitness theory, emphasizing a gene-centered view of evolution. Hamilton noted that genes can increase the replication of copies of themselves into the next generation by influencing the organism's social traits in such a way that (statistically) results in helping the survival and reproduction of other copies of the same genes (most simply, identical copies in the organism's close relatives). According to Hamilton's rule, self-sacrificing behaviors (and the genes influencing them) can evolve if they typically help the organism's close relatives so much that it more than compensates for the individual animal's sacrifice. Inclusive fitness theory resolved the issue of how altruism can evolve. Other theories also help explain the evolution of altruistic behavior, including evolutionary game theory, tit-for-tat reciprocity, and generalized reciprocity. These theories help to explain the development of altruistic behavior, and account for hostility toward cheaters (individuals that take advantage of others' altruism). 
Several mid-level evolutionary theories inform evolutionary psychology. The r/K selection theory proposes that some species prosper by having many offspring, while others follow the strategy of having fewer offspring but investing much more in each one. Humans follow the second strategy. Parental investment theory explains how parents invest more or less in individual offspring based on how successful those offspring are likely to be, and thus how much they might improve the parents' inclusive fitness. According to the Trivers–Willard hypothesis, parents in good conditions tend to invest more in sons (who are best able to take advantage of good conditions), while parents in poor conditions tend to invest more in daughters (who are best able to have successful offspring even in poor conditions). According to life history theory, animals evolve life histories to match their environments, determining details such as age at first reproduction and number of offspring. Dual inheritance theory posits that genes and human culture have interacted, with genes affecting the development of culture, and culture, in turn, affecting human evolution on a genetic level (see also the Baldwin effect).
Evolutionary psychology is based on the hypothesis that, just like hearts, lungs, livers, kidneys, and immune systems, cognition has functional structure that has a genetic basis, and therefore has evolved by natural selection. Like other organs and tissues, this functional structure should be universally shared amongst a species, and should solve important problems of survival and reproduction.
Evolutionary psychologists seek to understand psychological mechanisms by understanding the survival and reproductive functions they might have served over the course of evolutionary history.  [ page needed ] These might include abilities to infer others' emotions, discern kin from non-kin, identify and prefer healthier mates, cooperate with others and follow leaders. Consistent with the theory of natural selection, evolutionary psychology sees humans as often in conflict with others, including mates and relatives. For instance, a mother may wish to wean her offspring from breastfeeding earlier than does her infant, which frees up the mother to invest in additional offspring.   Evolutionary psychology also recognizes the role of kin selection and reciprocity in evolving prosocial traits such as altruism.  Like chimpanzees and bonobos, humans have subtle and flexible social instincts, allowing them to form extended families, lifelong friendships, and political alliances.  In studies testing theoretical predictions, evolutionary psychologists have made modest findings on topics such as infanticide, intelligence, marriage patterns, promiscuity, perception of beauty, bride price and parental investment. 
Historical topics Edit
Proponents of evolutionary psychology in the 1990s made some explorations in historical events, but the response from historical experts was highly negative and there has been little effort to continue that line of research. Historian Lynn Hunt says that the historians complained that the researchers:
have read the wrong studies, misinterpreted the results of experiments, or worse yet, turned to neuroscience looking for a universalizing, anti-representational and anti-intentional ontology to bolster their claims. 
Hunt states that, "the few attempts to build up a subfield of psychohistory collapsed under the weight of its presuppositions." She concludes that as of 2014 the "'iron curtain' between historians and psychology. remains standing." 
Products of evolution: adaptations, exaptations, byproducts, and random variation Edit
Not all traits of organisms are evolutionary adaptations. As noted in the table below, traits may also be exaptations, byproducts of adaptations (sometimes called "spandrels"), or random variation between individuals. 
Psychological adaptations are hypothesized to be innate or relatively easy to learn, and to manifest in cultures worldwide. For example, the ability of toddlers to learn a language with virtually no training is likely to be a psychological adaptation. On the other hand, ancestral humans did not read or write, thus today, learning to read and write require extensive training, and presumably involves the repurposing of cognitive capacities that evolved in response to selection pressures unrelated to written language.  However, variations in manifest behavior can result from universal mechanisms interacting with different local environments. For example, Caucasians who move from a northern climate to the equator will have darker skin. The mechanisms regulating their pigmentation do not change rather the input to those mechanisms change, resulting in different output.
|Definition||Organismic trait designed to solve an ancestral problem(s). Shows complexity, special "design", functionality||Adaptation that has been "re-purposed" to solve a different adaptive problem.||Byproduct of an adaptive mechanism with no current or ancestral function||Random variations in an adaptation or byproduct|
|Physiological example||Bones / Umbilical cord||Small bones of the inner ear||White color of bones / Belly button||Bumps on the skull, convex or concave belly button shape|
|Psychological example||Toddlers' ability to learn to talk with minimal instruction||Voluntary attention||Ability to learn to read and write||Variations in verbal intelligence|
One of the tasks of evolutionary psychology is to identify which psychological traits are likely to be adaptations, byproducts or random variation. George C. Williams suggested that an "adaptation is a special and onerous concept that should only be used where it is really necessary."  As noted by Williams and others, adaptations can be identified by their improbable complexity, species universality, and adaptive functionality.
Obligate and facultative adaptations Edit
A question that may be asked about an adaptation is whether it is generally obligate (relatively robust in the face of typical environmental variation) or facultative (sensitive to typical environmental variation).  The sweet taste of sugar and the pain of hitting one's knee against concrete are the result of fairly obligate psychological adaptations typical environmental variability during development does not much affect their operation. By contrast, facultative adaptations are somewhat like "if-then" statements. For example, adult attachment style seems particularly sensitive to early childhood experiences. As adults, the propensity to develop close, trusting bonds with others is dependent on whether early childhood caregivers could be trusted to provide reliable assistance and attention. The adaptation for skin to tan is conditional to exposure to sunlight this is an example of another facultative adaptation. When a psychological adaptation is facultative, evolutionary psychologists concern themselves with how developmental and environmental inputs influence the expression of the adaptation.
Cultural universals Edit
Evolutionary psychologists hold that behaviors or traits that occur universally in all cultures are good candidates for evolutionary adaptations.  Cultural universals include behaviors related to language, cognition, social roles, gender roles, and technology.  Evolved psychological adaptations (such as the ability to learn a language) interact with cultural inputs to produce specific behaviors (e.g., the specific language learned).
Basic gender differences, such as greater eagerness for sex among men and greater coyness among women,  are explained as sexually dimorphic psychological adaptations that reflect the different reproductive strategies of males and females.  
Evolutionary psychologists contrast their approach to what they term the "standard social science model," according to which the mind is a general-purpose cognition device shaped almost entirely by culture.  
Evolutionary psychology argues that to properly understand the functions of the brain, one must understand the properties of the environment in which the brain evolved. That environment is often referred to as the "environment of evolutionary adaptedness". 
The idea of an environment of evolutionary adaptedness was first explored as a part of attachment theory by John Bowlby.  This is the environment to which a particular evolved mechanism is adapted. More specifically, the environment of evolutionary adaptedness is defined as the set of historically recurring selection pressures that formed a given adaptation, as well as those aspects of the environment that were necessary for the proper development and functioning of the adaptation.
Humans, comprising the genus Homo, appeared between 1.5 and 2.5 million years ago, a time that roughly coincides with the start of the Pleistocene 2.6 million years ago. Because the Pleistocene ended a mere 12,000 years ago, most human adaptations either newly evolved during the Pleistocene, or were maintained by stabilizing selection during the Pleistocene. Evolutionary psychology therefore proposes that the majority of human psychological mechanisms are adapted to reproductive problems frequently encountered in Pleistocene environments.  In broad terms, these problems include those of growth, development, differentiation, maintenance, mating, parenting, and social relationships.
The environment of evolutionary adaptedness is significantly different from modern society.  The ancestors of modern humans lived in smaller groups, had more cohesive cultures, and had more stable and rich contexts for identity and meaning.  Researchers look to existing hunter-gatherer societies for clues as to how hunter-gatherers lived in the environment of evolutionary adaptedness.  Unfortunately, the few surviving hunter-gatherer societies are different from each other, and they have been pushed out of the best land and into harsh environments, so it is not clear how closely they reflect ancestral culture.  However, all around the world small-band hunter-gatherers offer a similar developmental system for the young ("hunter-gatherer childhood model," Konner, 2005 "evolved developmental niche" or "evolved nest" Narvaez et al., 2013). The characteristics of the niche are largely the same as for social mammals, who evolved over 30 million years ago: soothing perinatal experience, several years of on-request breastfeeding, nearly constant affection or physical proximity, responsiveness to need (mitigating offspring distress), self-directed play, and for humans, multiple responsive caregivers. Initial studies show the importance of these components in early life for positive child outcomes.  
Evolutionary psychologists sometimes look to chimpanzees, bonobos, and other great apes for insight into human ancestral behavior. 
Since an organism's adaptations were suited to its ancestral environment, a new and different environment can create a mismatch. Because humans are mostly adapted to Pleistocene environments, psychological mechanisms sometimes exhibit "mismatches" to the modern environment. One example is the fact that although about 10,000 people are killed with guns in the US annually,  whereas spiders and snakes kill only a handful, people nonetheless learn to fear spiders and snakes about as easily as they do a pointed gun, and more easily than an unpointed gun, rabbits or flowers.  A potential explanation is that spiders and snakes were a threat to human ancestors throughout the Pleistocene, whereas guns (and rabbits and flowers) were not. There is thus a mismatch between humans' evolved fear-learning psychology and the modern environment.  
This mismatch also shows up in the phenomena of the supernormal stimulus, a stimulus that elicits a response more strongly than the stimulus for which the response evolved. The term was coined by Niko Tinbergen to refer to non-human animal behavior, but psychologist Deirdre Barrett said that supernormal stimulation governs the behavior of humans as powerfully as that of other animals. She explained junk food as an exaggerated stimulus to cravings for salt, sugar, and fats,  and she says that television is an exaggeration of social cues of laughter, smiling faces and attention-grabbing action.  Magazine centerfolds and double cheeseburgers pull instincts intended for an environment of evolutionary adaptedness where breast development was a sign of health, youth and fertility in a prospective mate, and fat was a rare and vital nutrient.  The psychologist Mark van Vugt recently argued that modern organizational leadership is a mismatch.  His argument is that humans are not adapted to work in large, anonymous bureaucratic structures with formal hierarchies. The human mind still responds to personalized, charismatic leadership primarily in the context of informal, egalitarian settings. Hence the dissatisfaction and alienation that many employees experience. Salaries, bonuses and other privileges exploit instincts for relative status, which attract particularly males to senior executive positions. 
Evolutionary theory is heuristic in that it may generate hypotheses that might not be developed from other theoretical approaches. One of the major goals of adaptationist research is to identify which organismic traits are likely to be adaptations, and which are byproducts or random variations. As noted earlier, adaptations are expected to show evidence of complexity, functionality, and species universality, while byproducts or random variation will not. In addition, adaptations are expected to manifest as proximate mechanisms that interact with the environment in either a generally obligate or facultative fashion (see above). Evolutionary psychologists are also interested in identifying these proximate mechanisms (sometimes termed "mental mechanisms" or "psychological adaptations") and what type of information they take as input, how they process that information, and their outputs.  Evolutionary developmental psychology, or "evo-devo," focuses on how adaptations may be activated at certain developmental times (e.g., losing baby teeth, adolescence, etc.) or how events during the development of an individual may alter life history trajectories.
Evolutionary psychologists use several strategies to develop and test hypotheses about whether a psychological trait is likely to be an evolved adaptation. Buss (2011)  notes that these methods include:
Cross-cultural Consistency. Characteristics that have been demonstrated to be cross cultural human universals such as smiling, crying, facial expressions are presumed to be evolved psychological adaptations. Several evolutionary psychologists have collected massive datasets from cultures around the world to assess cross-cultural universality.
Function to Form (or "problem to solution"). The fact that males, but not females, risk potential misidentification of genetic offspring (referred to as "paternity insecurity") led evolutionary psychologists to hypothesize that, compared to females, male jealousy would be more focused on sexual, rather than emotional, infidelity.
Form to Function (reverse-engineering – or "solution to problem"). Morning sickness, and associated aversions to certain types of food, during pregnancy seemed to have the characteristics of an evolved adaptation (complexity and universality). Margie Profet hypothesized that the function was to avoid the ingestion of toxins during early pregnancy that could damage fetus (but which are otherwise likely to be harmless to healthy non-pregnant women).
Corresponding Neurological Modules. Evolutionary psychology and cognitive neuropsychology are mutually compatible – evolutionary psychology helps to identify psychological adaptations and their ultimate, evolutionary functions, while neuropsychology helps to identify the proximate manifestations of these adaptations.
Current evolutionary Adaptiveness. In addition to evolutionary models that suggest evolution occurs across large spans of time, recent research has demonstrated that some evolutionary shifts can be fast and dramatic. Consequently, some evolutionary psychologists have focused on the impact of psychological traits in the current environment. Such research can be used to inform estimates of the prevalence of traits over time. Such work has been informative in studying evolutionary psychopathology. 
Evolutionary psychologists also use various sources of data for testing, including experiments, archaeological records, data from hunter-gatherer societies, observational studies, neuroscience data, self-reports and surveys, public records, and human products.  Recently, additional methods and tools have been introduced based on fictional scenarios,  mathematical models,  and multi-agent computer simulations. 
Foundational areas of research in evolutionary psychology can be divided into broad categories of adaptive problems that arise from the theory of evolution itself: survival, mating, parenting, family and kinship, interactions with non-kin, and cultural evolution.
Survival and individual-level psychological adaptations Edit
Problems of survival are clear targets for the evolution of physical and psychological adaptations. Major problems the ancestors of present-day humans faced included food selection and acquisition territory selection and physical shelter and avoiding predators and other environmental threats. 
Consciousness meets George Williams' criteria of species universality, complexity,  and functionality, and it is a trait that apparently increases fitness. 
In his paper "Evolution of consciousness," John Eccles argues that special anatomical and physical adaptations of the mammalian cerebral cortex gave rise to consciousness.  In contrast, others have argued that the recursive circuitry underwriting consciousness is much more primitive, having evolved initially in pre-mammalian species because it improves the capacity for interaction with both social and natural environments by providing an energy-saving "neutral" gear in an otherwise energy-expensive motor output machine.  Once in place, this recursive circuitry may well have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms, as outlined by Bernard J. Baars.  Richard Dawkins suggested that humans evolved consciousness in order to make themselves the subjects of thought.  Daniel Povinelli suggests that large, tree-climbing apes evolved consciousness to take into account one's own mass when moving safely among tree branches.  Consistent with this hypothesis, Gordon Gallup found that chimps and orangutans, but not little monkeys or terrestrial gorillas, demonstrated self-awareness in mirror tests. 
The concept of consciousness can refer to voluntary action, awareness, or wakefulness. However, even voluntary behavior involves unconscious mechanisms. Many cognitive processes take place in the cognitive unconscious, unavailable to conscious awareness. Some behaviors are conscious when learned but then become unconscious, seemingly automatic. Learning, especially implicitly learning a skill, can take place outside of consciousness. For example, plenty of people know how to turn right when they ride a bike, but very few can accurately explain how they actually do so. Evolutionary psychology approaches self-deception as an adaptation that can improve one's results in social exchanges. 
Sleep may have evolved to conserve energy when activity would be less fruitful or more dangerous, such as at night, and especially during the winter season. 
Sensation and perception Edit
Many experts, such as Jerry Fodor, write that the purpose of perception is knowledge, but evolutionary psychologists hold that its primary purpose is to guide action.  For example, they say, depth perception seems to have evolved not to help us know the distances to other objects but rather to help us move around in space.  Evolutionary psychologists say that animals from fiddler crabs to humans use eyesight for collision avoidance, suggesting that vision is basically for directing action, not providing knowledge. 
Building and maintaining sense organs is metabolically expensive, so these organs evolve only when they improve an organism's fitness.  More than half the brain is devoted to processing sensory information, and the brain itself consumes roughly one-fourth of one's metabolic resources, so the senses must provide exceptional benefits to fitness.  Perception accurately mirrors the world animals get useful, accurate information through their senses. 
Scientists who study perception and sensation have long understood the human senses as adaptations to their surrounding worlds.  Depth perception consists of processing over half a dozen visual cues, each of which is based on a regularity of the physical world.  Vision evolved to respond to the narrow range of electromagnetic energy that is plentiful and that does not pass through objects.  Sound waves go around corners and interact with obstacles, creating a complex pattern that includes useful information about the sources of and distances to objects.  Larger animals naturally make lower-pitched sounds as a consequence of their size.  The range over which an animal hears, on the other hand, is determined by adaptation. Homing pigeons, for example, can hear very low-pitched sound (infrasound) that carries great distances, even though most smaller animals detect higher-pitched sounds.  Taste and smell respond to chemicals in the environment that are thought to have been significant for fitness in the environment of evolutionary adaptedness.  For example, salt and sugar were apparently both valuable to the human or pre-human inhabitants of the environment of evolutionary adaptedness, so present day humans have an intrinsic hunger for salty and sweet tastes.  The sense of touch is actually many senses, including pressure, heat, cold, tickle, and pain.  Pain, while unpleasant, is adaptive.  An important adaptation for senses is range shifting, by which the organism becomes temporarily more or less sensitive to sensation.  For example, one's eyes automatically adjust to dim or bright ambient light.  Sensory abilities of different organisms often coevolve, as is the case with the hearing of echolocating bats and that of the moths that have evolved to respond to the sounds that the bats make. 
Evolutionary psychologists contend that perception demonstrates the principle of modularity, with specialized mechanisms handling particular perception tasks.  For example, people with damage to a particular part of the brain suffer from the specific defect of not being able to recognize faces (prosopagnosia).  Evolutionary psychology suggests that this indicates a so-called face-reading module. 
Learning and facultative adaptations Edit
In evolutionary psychology, learning is said to be accomplished through evolved capacities, specifically facultative adaptations.  Facultative adaptations express themselves differently depending on input from the environment.  Sometimes the input comes during development and helps shape that development.  For example, migrating birds learn to orient themselves by the stars during a critical period in their maturation.  Evolutionary psychologists believe that humans also learn language along an evolved program, also with critical periods.  The input can also come during daily tasks, helping the organism cope with changing environmental conditions.  For example, animals evolved Pavlovian conditioning in order to solve problems about causal relationships.  Animals accomplish learning tasks most easily when those tasks resemble problems that they faced in their evolutionary past, such as a rat learning where to find food or water.  Learning capacities sometimes demonstrate differences between the sexes.  In many animal species, for example, males can solve spatial problem faster and more accurately than females, due to the effects of male hormones during development.  The same might be true of humans. 
Emotion and motivation Edit
Motivations direct and energize behavior, while emotions provide the affective component to motivation, positive or negative.  In the early 1970s, Paul Ekman and colleagues began a line of research which suggests that many emotions are universal.  He found evidence that humans share at least five basic emotions: fear, sadness, happiness, anger, and disgust.  Social emotions evidently evolved to motivate social behaviors that were adaptive in the environment of evolutionary adaptedness.  For example, spite seems to work against the individual but it can establish an individual's reputation as someone to be feared.  Shame and pride can motivate behaviors that help one maintain one's standing in a community, and self-esteem is one's estimate of one's status.   Motivation has a neurobiological basis in the reward system of the brain. Recently, it has been suggested that reward systems may evolve in such a way that there may be an inherent or unavoidable trade-off in the motivational system for activities of short versus long duration. 
Cognition refers to internal representations of the world and internal information processing. From an evolutionary psychology perspective, cognition is not "general purpose," but uses heuristics, or strategies, that generally increase the likelihood of solving problems that the ancestors of present-day humans routinely faced. For example, present day humans are far more likely to solve logic problems that involve detecting cheating (a common problem given humans' social nature) than the same logic problem put in purely abstract terms.  Since the ancestors of present-day humans did not encounter truly random events, present day humans may be cognitively predisposed to incorrectly identify patterns in random sequences. "Gamblers' Fallacy" is one example of this. Gamblers may falsely believe that they have hit a "lucky streak" even when each outcome is actually random and independent of previous trials. Most people believe that if a fair coin has been flipped 9 times and Heads appears each time, that on the tenth flip, there is a greater than 50% chance of getting Tails.  Humans find it far easier to make diagnoses or predictions using frequency data than when the same information is presented as probabilities or percentages, presumably because the ancestors of present-day humans lived in relatively small tribes (usually with fewer than 150 people) where frequency information was more readily available. 
Evolutionary psychology is primarily interested in finding commonalities between people, or basic human psychological nature. From an evolutionary perspective, the fact that people have fundamental differences in personality traits initially presents something of a puzzle.  (Note: The field of behavioral genetics is concerned with statistically partitioning differences between people into genetic and environmental sources of variance. However, understanding the concept of heritability can be tricky – heritability refers only to the differences between people, never the degree to which the traits of an individual are due to environmental or genetic factors, since traits are always a complex interweaving of both.)
Personality traits are conceptualized by evolutionary psychologists as due to normal variation around an optimum, due to frequency-dependent selection (behavioral polymorphisms), or as facultative adaptations. Like variability in height, some personality traits may simply reflect inter-individual variability around a general optimum.  Or, personality traits may represent different genetically predisposed "behavioral morphs" – alternate behavioral strategies that depend on the frequency of competing behavioral strategies in the population. For example, if most of the population is generally trusting and gullible, the behavioral morph of being a "cheater" (or, in the extreme case, a sociopath) may be advantageous.  Finally, like many other psychological adaptations, personality traits may be facultative – sensitive to typical variations in the social environment, especially during early development. For example, later born children are more likely than first borns to be rebellious, less conscientious and more open to new experiences, which may be advantageous to them given their particular niche in family structure.  It is important to note that shared environmental influences do play a role in personality and are not always of less importance than genetic factors. However, shared environmental influences often decrease to near zero after adolescence but do not completely disappear. 
According to Steven Pinker, who builds on the work by Noam Chomsky, the universal human ability to learn to talk between the ages of 1 – 4, basically without training, suggests that language acquisition is a distinctly human psychological adaptation (see, in particular, Pinker's The Language Instinct). Pinker and Bloom (1990) argue that language as a mental faculty shares many likenesses with the complex organs of the body which suggests that, like these organs, language has evolved as an adaptation, since this is the only known mechanism by which such complex organs can develop. 
Pinker follows Chomsky in arguing that the fact that children can learn any human language with no explicit instruction suggests that language, including most of grammar, is basically innate and that it only needs to be activated by interaction. Chomsky himself does not believe language to have evolved as an adaptation, but suggests that it likely evolved as a byproduct of some other adaptation, a so-called spandrel. But Pinker and Bloom argue that the organic nature of language strongly suggests that it has an adaptational origin. 
Evolutionary psychologists hold that the FOXP2 gene may well be associated with the evolution of human language.  In the 1980s, psycholinguist Myrna Gopnik identified a dominant gene that causes language impairment in the KE family of Britain.  This gene turned out to be a mutation of the FOXP2 gene.  Humans have a unique allele of this gene, which has otherwise been closely conserved through most of mammalian evolutionary history.  This unique allele seems to have first appeared between 100 and 200 thousand years ago, and it is now all but universal in humans.  However, the once-popular idea that FOXP2 is a 'grammar gene' or that it triggered the emergence of language in Homo sapiens is now widely discredited. 
Currently several competing theories about the evolutionary origin of language coexist, none of them having achieved a general consensus.  Researchers of language acquisition in primates and humans such as Michael Tomasello and Talmy Givón, argue that the innatist framework has understated the role of imitation in learning and that it is not at all necessary to posit the existence of an innate grammar module to explain human language acquisition. Tomasello argues that studies of how children and primates actually acquire communicative skills suggests that humans learn complex behavior through experience, so that instead of a module specifically dedicated to language acquisition, language is acquired by the same cognitive mechanisms that are used to acquire all other kinds of socially transmitted behavior. 
On the issue of whether language is best seen as having evolved as an adaptation or as a spandrel, evolutionary biologist W. Tecumseh Fitch, following Stephen J. Gould, argues that it is unwarranted to assume that every aspect of language is an adaptation, or that language as a whole is an adaptation. He criticizes some strands of evolutionary psychology for suggesting a pan-adaptionist view of evolution, and dismisses Pinker and Bloom's question of whether "Language has evolved as an adaptation" as being misleading. He argues instead that from a biological viewpoint the evolutionary origins of language is best conceptualized as being the probable result of a convergence of many separate adaptations into a complex system.  A similar argument is made by Terrence Deacon who in The Symbolic Species argues that the different features of language have co-evolved with the evolution of the mind and that the ability to use symbolic communication is integrated in all other cognitive processes. 
If the theory that language could have evolved as a single adaptation is accepted, the question becomes which of its many functions has been the basis of adaptation. Several evolutionary hypotheses have been posited: that language evolved for the purpose of social grooming, that it evolved as a way to show mating potential or that it evolved to form social contracts. Evolutionary psychologists recognize that these theories are all speculative and that much more evidence is required to understand how language might have been selectively adapted. 
Given that sexual reproduction is the means by which genes are propagated into future generations, sexual selection plays a large role in human evolution. Human mating, then, is of interest to evolutionary psychologists who aim to investigate evolved mechanisms to attract and secure mates.  Several lines of research have stemmed from this interest, such as studies of mate selection    mate poaching,  mate retention,  mating preferences  and conflict between the sexes. 
In 1972 Robert Trivers published an influential paper  on sex differences that is now referred to as parental investment theory. The size differences of gametes (anisogamy) is the fundamental, defining difference between males (small gametes – sperm) and females (large gametes – ova). Trivers noted that anisogamy typically results in different levels of parental investment between the sexes, with females initially investing more. Trivers proposed that this difference in parental investment leads to the sexual selection of different reproductive strategies between the sexes and to sexual conflict. For example, he suggested that the sex that invests less in offspring will generally compete for access to the higher-investing sex to increase their inclusive fitness (also see Bateman's principle  ). Trivers posited that differential parental investment led to the evolution of sexual dimorphisms in mate choice, intra- and inter- sexual reproductive competition, and courtship displays. In mammals, including humans, females make a much larger parental investment than males (i.e. gestation followed by childbirth and lactation). Parental investment theory is a branch of life history theory.
Buss and Schmitt's (1993) Sexual Strategies Theory  proposed that, due to differential parental investment, humans have evolved sexually dimorphic adaptations related to "sexual accessibility, fertility assessment, commitment seeking and avoidance, immediate and enduring resource procurement, paternity certainty, assessment of mate value, and parental investment." Their Strategic Interference Theory  suggested that conflict between the sexes occurs when the preferred reproductive strategies of one sex interfere with those of the other sex, resulting in the activation of emotional responses such as anger or jealousy.
Women are generally more selective when choosing mates, especially under long term mating conditions. However, under some circumstances, short term mating can provide benefits to women as well, such as fertility insurance, trading up to better genes, reducing risk of inbreeding, and insurance protection of her offspring. 
Due to male paternity insecurity, sex differences have been found in the domains of sexual jealousy.   Females generally react more adversely to emotional infidelity and males will react more to sexual infidelity. This particular pattern is predicted because the costs involved in mating for each sex are distinct. Women, on average, should prefer a mate who can offer resources (e.g., financial, commitment), thus, a woman risks losing such resources with a mate who commits emotional infidelity. Men, on the other hand, are never certain of the genetic paternity of their children because they do not bear the offspring themselves ("paternity insecurity"). This suggests that for men sexual infidelity would generally be more aversive than emotional infidelity because investing resources in another man's offspring does not lead to propagation of their own genes. 
Another interesting line of research is that which examines women's mate preferences across the ovulatory cycle.   The theoretical underpinning of this research is that ancestral women would have evolved mechanisms to select mates with certain traits depending on their hormonal status. Known as the ovulatory shift hypothesis, the theory posits that, during the ovulatory phase of a woman's cycle (approximately days 10–15 of a woman's cycle),  a woman who mated with a male with high genetic quality would have been more likely, on average, to produce and bear a healthy offspring than a woman who mated with a male with low genetic quality. These putative preferences are predicted to be especially apparent for short-term mating domains because a potential male mate would only be offering genes to a potential offspring. This hypothesis allows researchers to examine whether women select mates who have characteristics that indicate high genetic quality during the high fertility phase of their ovulatory cycles. Indeed, studies have shown that women's preferences vary across the ovulatory cycle. In particular, Haselton and Miller (2006) showed that highly fertile women prefer creative but poor men as short-term mates. Creativity may be a proxy for good genes.  Research by Gangestad et al. (2004) indicates that highly fertile women prefer men who display social presence and intrasexual competition these traits may act as cues that would help women predict which men may have, or would be able to acquire, resources.
Reproduction is always costly for women, and can also be for men. Individuals are limited in the degree to which they can devote time and resources to producing and raising their young, and such expenditure may also be detrimental to their future condition, survival and further reproductive output. Parental investment is any parental expenditure (time, energy etc.) that benefits one offspring at a cost to parents' ability to invest in other components of fitness (Clutton-Brock 1991: 9 Trivers 1972). Components of fitness (Beatty 1992) include the well-being of existing offspring, parents' future reproduction, and inclusive fitness through aid to kin (Hamilton, 1964). Parental investment theory is a branch of life history theory.
Robert Trivers' theory of parental investment predicts that the sex making the largest investment in lactation, nurturing and protecting offspring will be more discriminating in mating and that the sex that invests less in offspring will compete for access to the higher investing sex (see Bateman's principle).  Sex differences in parental effort are important in determining the strength of sexual selection.
The benefits of parental investment to the offspring are large and are associated with the effects on condition, growth, survival and ultimately, on reproductive success of the offspring. However, these benefits can come at the cost of parent's ability to reproduce in the future e.g. through the increased risk of injury when defending offspring against predators, the loss of mating opportunities whilst rearing offspring and an increase in the time to the next reproduction. Overall, parents are selected to maximize the difference between the benefits and the costs, and parental care will likely evolve when the benefits exceed the costs.
The Cinderella effect is an alleged high incidence of stepchildren being physically, emotionally or sexually abused, neglected, murdered, or otherwise mistreated at the hands of their stepparents at significantly higher rates than their genetic counterparts. It takes its name from the fairy tale character Cinderella, who in the story was cruelly mistreated by her stepmother and stepsisters.  Daly and Wilson (1996) noted: "Evolutionary thinking led to the discovery of the most important risk factor for child homicide – the presence of a stepparent. Parental efforts and investments are valuable resources, and selection favors those parental psyches that allocate effort effectively to promote fitness. The adaptive problems that challenge parental decision making include both the accurate identification of one's offspring and the allocation of one's resources among them with sensitivity to their needs and abilities to convert parental investment into fitness increments…. Stepchildren were seldom or never so valuable to one's expected fitness as one's own offspring would be, and those parental psyches that were easily parasitized by just any appealing youngster must always have incurred a selective disadvantage"(Daly & Wilson, 1996, pp. 64–65). However, they note that not all stepparents will "want" to abuse their partner's children, or that genetic parenthood is any insurance against abuse. They see step parental care as primarily "mating effort" towards the genetic parent. 
Family and kin Edit
Inclusive fitness is the sum of an organism's classical fitness (how many of its own offspring it produces and supports) and the number of equivalents of its own offspring it can add to the population by supporting others.  The first component is called classical fitness by Hamilton (1964).
From the gene's point of view, evolutionary success ultimately depends on leaving behind the maximum number of copies of itself in the population. Until 1964, it was generally believed that genes only achieved this by causing the individual to leave the maximum number of viable offspring. However, in 1964 W. D. Hamilton proved mathematically that, because close relatives of an organism share some identical genes, a gene can also increase its evolutionary success by promoting the reproduction and survival of these related or otherwise similar individuals. Hamilton concluded that this leads natural selection to favor organisms that would behave in ways that maximize their inclusive fitness. It is also true that natural selection favors behavior that maximizes personal fitness.
Hamilton's rule describes mathematically whether or not a gene for altruistic behavior will spread in a population:
The concept serves to explain how natural selection can perpetuate altruism. If there is an "altruism gene" (or complex of genes) that influences an organism's behavior to be helpful and protective of relatives and their offspring, this behavior also increases the proportion of the altruism gene in the population, because relatives are likely to share genes with the altruist due to common descent. Altruists may also have some way to recognize altruistic behavior in unrelated individuals and be inclined to support them. As Dawkins points out in The Selfish Gene (Chapter 6) and The Extended Phenotype,  this must be distinguished from the green-beard effect.
Although it is generally true that humans tend to be more altruistic toward their kin than toward non-kin, the relevant proximate mechanisms that mediate this cooperation have been debated (see kin recognition), with some arguing that kin status is determined primarily via social and cultural factors (such as co-residence, maternal association of sibs, etc.),  while others have argued that kin recognition can also be mediated by biological factors such as facial resemblance and immunogenetic similarity of the major histocompatibility complex (MHC).  For a discussion of the interaction of these social and biological kin recognition factors see Lieberman, Tooby, and Cosmides (2007)  (PDF).
Whatever the proximate mechanisms of kin recognition there is substantial evidence that humans act generally more altruistically to close genetic kin compared to genetic non-kin.   
Interactions with non-kin / reciprocity Edit
Although interactions with non-kin are generally less altruistic compared to those with kin, cooperation can be maintained with non-kin via mutually beneficial reciprocity as was proposed by Robert Trivers.  If there are repeated encounters between the same two players in an evolutionary game in which each of them can choose either to "cooperate" or "defect," then a strategy of mutual cooperation may be favored even if it pays each player, in the short term, to defect when the other cooperates. Direct reciprocity can lead to the evolution of cooperation only if the probability, w, of another encounter between the same two individuals exceeds the cost-to-benefit ratio of the altruistic act:
Reciprocity can also be indirect if information about previous interactions is shared. Reputation allows evolution of cooperation by indirect reciprocity. Natural selection favors strategies that base the decision to help on the reputation of the recipient: studies show that people who are more helpful are more likely to receive help. The calculations of indirect reciprocity are complicated and only a tiny fraction of this universe has been uncovered, but again a simple rule has emerged.  Indirect reciprocity can only promote cooperation if the probability, q, of knowing someone's reputation exceeds the cost-to-benefit ratio of the altruistic act:
One important problem with this explanation is that individuals may be able to evolve the capacity to obscure their reputation, reducing the probability, q, that it will be known. 
Trivers argues that friendship and various social emotions evolved in order to manage reciprocity.  Liking and disliking, he says, evolved to help present day humans' ancestors form coalitions with others who reciprocated and to exclude those who did not reciprocate.  Moral indignation may have evolved to prevent one's altruism from being exploited by cheaters, and gratitude may have motivated present day humans' ancestors to reciprocate appropriately after benefiting from others' altruism.  Likewise, present day humans feel guilty when they fail to reciprocate.  These social motivations match what evolutionary psychologists expect to see in adaptations that evolved to maximize the benefits and minimize the drawbacks of reciprocity. 
Evolutionary psychologists say that humans have psychological adaptations that evolved specifically to help us identify nonreciprocators, commonly referred to as "cheaters."  In 1993, Robert Frank and his associates found that participants in a prisoner's dilemma scenario were often able to predict whether their partners would "cheat," based on a half-hour of unstructured social interaction.  In a 1996 experiment, for example, Linda Mealey and her colleagues found that people were better at remembering the faces of people when those faces were associated with stories about those individuals cheating (such as embezzling money from a church). 
Strong reciprocity (or "tribal reciprocity") Edit
Humans may have an evolved set of psychological adaptations that predispose them to be more cooperative than otherwise would be expected with members of their tribal in-group, and, more nasty to members of tribal out groups. These adaptations may have been a consequence of tribal warfare.  Humans may also have predispositions for "altruistic punishment" – to punish in-group members who violate in-group rules, even when this altruistic behavior cannot be justified in terms of helping those you are related to (kin selection), cooperating with those who you will interact with again (direct reciprocity), or cooperating to better your reputation with others (indirect reciprocity).  
Though evolutionary psychology has traditionally focused on individual-level behaviors, determined by species-typical psychological adaptations, considerable work has been done on how these adaptations shape and, ultimately govern, culture (Tooby and Cosmides, 1989).  Tooby and Cosmides (1989) argued that the mind consists of many domain-specific psychological adaptations, some of which may constrain what cultural material is learned or taught. As opposed to a domain-general cultural acquisition program, where an individual passively receives culturally-transmitted material from the group, Tooby and Cosmides (1989), among others, argue that: "the psyche evolved to generate adaptive rather than repetitive behavior, and hence critically analyzes the behavior of those surrounding it in highly structured and patterned ways, to be used as a rich (but by no means the only) source of information out of which to construct a 'private culture' or individually tailored adaptive system in consequence, this system may or may not mirror the behavior of others in any given respect." (Tooby and Cosmides 1989). 
Developmental psychology Edit
According to Paul Baltes, the benefits granted by evolutionary selection decrease with age. Natural selection has not eliminated many harmful conditions and nonadaptive characteristics that appear among older adults, such as Alzheimer disease. If it were a disease that killed 20-year-olds instead of 70-year-olds this may have been a disease that natural selection could have eliminated ages ago. Thus, unaided by evolutionary pressures against nonadaptive conditions, modern humans suffer the aches, pains, and infirmities of aging and as the benefits of evolutionary selection decrease with age, the need for modern technological mediums against non-adaptive conditions increases. 
Social psychology Edit
As humans are a highly social species, there are many adaptive problems associated with navigating the social world (e.g., maintaining allies, managing status hierarchies, interacting with outgroup members, coordinating social activities, collective decision-making). Researchers in the emerging field of evolutionary social psychology have made many discoveries pertaining to topics traditionally studied by social psychologists, including person perception, social cognition, attitudes, altruism, emotions, group dynamics, leadership, motivation, prejudice, intergroup relations, and cross-cultural differences.    
When endeavouring to solve a problem humans at an early age show determination while chimpanzees have no comparable facial expression. Researchers suspect the human determined expression evolved because when a human is determinedly working on a problem other people will frequently help. 
Abnormal psychology Edit
Adaptationist hypotheses regarding the etiology of psychological disorders are often based on analogies between physiological and psychological dysfunctions,  as noted in the table below. Prominent theorists and evolutionary psychiatrists include Michael T. McGuire, Anthony Stevens, and Randolph M. Nesse. They, and others, suggest that mental disorders are due to the interactive effects of both nature and nurture, and often have multiple contributing causes. 
|Causal mechanism of failure or malfunction of adaptation||Physiological Example||Hypothesized Psychological Example|
|Functioning adaptation (adaptive defense)||Fever / Vomiting |
(functional responses to infection or ingestion of toxins)
|Mild depression or anxiety (functional responses to mild loss or stress  / reduction of social interactions to prevent infection by contagious pathogens) |
|By-product of an adaptation(s)||Intestinal gas |
(byproduct of digestion of fiber)
|Sexual fetishes (?)|
(possible byproduct of normal sexual arousal adaptations that have 'imprinted' on unusual objects or situations)
|Adaptations with multiple effects||Sickle cell disease (Gene that imparts malaria resistance, in homozygous form, causes sickle cell anemia)||Schizophrenia or bipolar disorder (May be side-effects of adaptations for high levels of creativity, perhaps dependent on alternate developmental trajectories)|
|Malfunctioning adaptation||Allergies |
(over-reactive immunological responses)
(possible malfunctioning of theory of mind module)
|Frequency-dependent morphs||The two sexes / Different blood and immune system types||Personality disorders |
(may represent alternative behavioral strategies possibly dependent on its prevalence in the population)
|Mismatch between ancestral & current environments||Type 2 Diabetes |
(May be related to the abundance of sugary foods in the modern world)
|More frequent modern interaction with strangers (compared to family and close friends) may predispose greater incidence of depression & anxiety|
|Tails of normal distribution (bell curve)||Dwarfism or gigantism||Extremities of the distribution of cognitive and personality traits|
(e.g., extremely introversion and extraversion, or intellectual giftedness and intellectual disability)
Evolutionary psychologists have suggested that schizophrenia and bipolar disorder may reflect a side-effect of genes with fitness benefits, such as increased creativity.  (Some individuals with bipolar disorder are especially creative during their manic phases and the close relatives of people with schizophrenia have been found to be more likely to have creative professions.  ) A 1994 report by the American Psychiatry Association found that people suffered from schizophrenia at roughly the same rate in Western and non-Western cultures, and in industrialized and pastoral societies, suggesting that schizophrenia is not a disease of civilization nor an arbitrary social invention.  Sociopathy may represent an evolutionarily stable strategy, by which a small number of people who cheat on social contracts benefit in a society consisting mostly of non-sociopaths.  Mild depression may be an adaptive response to withdraw from, and re-evaluate, situations that have led to disadvantageous outcomes (the "analytical rumination hypothesis")  (see Evolutionary approaches to depression).
Some of these speculations have yet to be developed into fully testable hypotheses, and a great deal of research is required to confirm their validity.  
Antisocial and criminal behavior Edit
Evolutionary psychology has been applied to explain criminal or otherwise immoral behavior as being adaptive or related to adaptive behaviors. Males are generally more aggressive than females, who are more selective of their partners because of the far greater effort they have to contribute to pregnancy and child-rearing. Males being more aggressive is hypothesized to stem from the more intense reproductive competition faced by them. Males of low status may be especially vulnerable to being childless. It may have been evolutionary advantageous to engage in highly risky and violently aggressive behavior to increase their status and therefore reproductive success. This may explain why males are generally involved in more crimes, and why low status and being unmarried is associated with criminality. Furthermore, competition over females is argued to have been particularly intensive in late adolescence and young adulthood, which is theorized to explain why crime rates are particularly high during this period.  Some sociologists have underlined differential exposure to androgens as the cause of these behaviors, notably Lee Ellis in his evolutionary neuroandrogenic (ENA) theory. 
Many conflicts that result in harm and death involve status, reputation, and seemingly trivial insults.  Steven Pinker in his book The Blank Slate argues that in non-state societies without a police it was very important to have a credible deterrence against aggression. Therefore, it was important to be perceived as having a credible reputation for retaliation, resulting in humans to develop instincts for revenge as well as for protecting reputation ("honor"). Pinker argues that the development of the state and the police have dramatically reduced the level of violence compared to the ancestral environment. Whenever the state breaks down, which can be very locally such as in poor areas of a city, humans again organize in groups for protection and aggression and concepts such as violent revenge and protecting honor again become extremely important. 
Rape is theorized to be a reproductive strategy that facilitates the propagation of the rapist's progeny. Such a strategy may be adopted by men who otherwise are unlikely to be appealing to women and therefore cannot form legitimate relationships, or by high status men on socially vulnerable women who are unlikely to retaliate to increase their reproductive success even further.  The sociobiological theories of rape are highly controversial, as traditional theories typically do not consider rape to be a behavioral adaptation, and objections to this theory are made on ethical, religious, political, as well as scientific grounds.
Psychology of religion Edit
Adaptationist perspectives on religious belief suggest that, like all behavior, religious behaviors are a product of the human brain. As with all other organ functions, cognition's functional structure has been argued to have a genetic foundation, and is therefore subject to the effects of natural selection and sexual selection. Like other organs and tissues, this functional structure should be universally shared amongst humans and should have solved important problems of survival and reproduction in ancestral environments. However, evolutionary psychologists remain divided on whether religious belief is more likely a consequence of evolved psychological adaptations,  or a byproduct of other cognitive adaptations. 
Coalitional psychology Edit
Coalitional psychology is an approach to explain political behaviors between different coalitions and the conditionality of these behaviors in evolutionary psychological perspective. This approach assumes that since human beings appeared on the earth, they have evolved to live in groups instead of living as individuals to achieve benefits such as more mating opportunities and increased status.  Human beings thus naturally think and act in a way that manages and negotiates group dynamics.
Coalitional psychology offers falsifiable ex ante prediction by positing five hypotheses on how these psychological adaptations operate: 
- Humans represent groups as a special category of individual, unstable and with a short shadow of the future strategically manipulate the coalitional environment, often appealing to emotional devices such as "outrage" to inspire collective action. dominate relations with enemies, whereas absolute gains characterize relations with allies.
- Coalitional size and male physical strength will positively predict individual support for aggressive foreign policies.
- Individuals with children, particularly women, will vary in adopting aggressive foreign policies than those without progeny.
Critics of evolutionary psychology accuse it of promoting genetic determinism, panadaptationism (the idea that all behaviors and anatomical features are adaptations), unfalsifiable hypotheses, distal or ultimate explanations of behavior when proximate explanations are superior, and malevolent political or moral ideas. 
Ethical implications Edit
Critics have argued that evolutionary psychology might be used to justify existing social hierarchies and reactionary policies.   It has also been suggested by critics that evolutionary psychologists' theories and interpretations of empirical data rely heavily on ideological assumptions about race and gender. 
In response to such criticism, evolutionary psychologists often caution against committing the naturalistic fallacy – the assumption that "what is natural" is necessarily a moral good.   [ page needed ]  However, their caution against committing the naturalistic fallacy has been criticized as means to stifle legitimate ethical discussions. 
Contradictions in models Edit
Some criticisms of evolutionary psychology point at contradictions between different aspects of adaptive scenarios posited by evolutionary psychology. One example is the evolutionary psychology model of extended social groups selecting for modern human brains, a contradiction being that the synaptic function of modern human brains require high amounts of many specific essential nutrients so that such a transition to higher requirements of the same essential nutrients being shared by all individuals in a population would decrease the possibility of forming large groups due to bottleneck foods with rare essential nutrients capping group sizes. It is mentioned that some insects have societies with different ranks for each individual and that monkeys remain socially functioning after removal of most of the brain as additional arguments against big brains promoting social networking. The model of males as both providers and protectors is criticized for the impossibility of being in two places at once, the male cannot both protect his family at home and be out hunting at the same time. In the case of the claim that a provider male could buy protection service for his family from other males by bartering food that he had hunted, critics point at the fact that the most valuable food (the food that contained the rarest essential nutrients) would be different in different ecologies and as such vegetable in some geographical areas and animal in others, making it impossible for hunting styles relying on physical strength or risk taking to be universally of similar value in bartered food and instead making it inevitable that in some parts of Africa, food gathered with no need for major physical strength would be the most valuable to barter for protection. A contradiction between evolutionary psychology's claim of men needing to be more sexually visual than women for fast speed of assessing women's fertility than women needed to be able to assess the male's genes and its claim of male sexual jealousy guarding against infidelity is also pointed at, as it would be pointless for a male to be fast to assess female fertility if he needed to assess the risk of there being a jealous male mate and in that case his chances of defeating him before mating anyway (pointlessness of assessing one necessary condition faster than another necessary condition can possibly be assessed).  
Standard social science model Edit
Evolutionary psychology has been entangled in the larger philosophical and social science controversies related to the debate on nature versus nurture. Evolutionary psychologists typically contrast evolutionary psychology with what they call the standard social science model (SSSM). They characterize the SSSM as the "blank slate", "relativist", "social constructionist", and "cultural determinist" perspective that they say dominated the social sciences throughout the 20th century and assumed that the mind was shaped almost entirely by culture. 
Critics have argued that evolutionary psychologists created a false dichotomy between their own view and the caricature of the SSSM.    Other critics regard the SSSM as a rhetorical device or a straw man    and suggest that the scientists whom evolutionary psychologists associate with the SSSM did not believe that the mind was a blank state devoid of any natural predispositions. 
Reductionism and determinism Edit
Some critics view evolutionary psychology as a form of genetic reductionism and genetic determinism,   a common critique being that evolutionary psychology does not address the complexity of individual development and experience and fails to explain the influence of genes on behavior in individual cases.  Evolutionary psychologists respond that they are working within a nature-nurture interactionist framework that acknowledges that many psychological adaptations are facultative (sensitive to environmental variations during individual development). The discipline is generally not focused on proximate analyses of behavior, but rather its focus is on the study of distal/ultimate causality (the evolution of psychological adaptations). The field of behavioral genetics is focused on the study of the proximate influence of genes on behavior. 
Testability of hypotheses Edit
A frequent critique of the discipline is that the hypotheses of evolutionary psychology are frequently arbitrary and difficult or impossible to adequately test, thus questioning its status as an actual scientific discipline, for example because many current traits probably evolved to serve different functions than they do now.   Thus because there are a potentially infinite number of alternative explanations for why a trait evolved, critics contend that it is impossible to determine the exact explanation.  While evolutionary psychology hypotheses are difficult to test, evolutionary psychologists assert that it is not impossible.  Part of the critique of the scientific base of evolutionary psychology includes a critique of the concept of the Environment of Evolutionary Adaptation (EEA). Some critics have argued that researchers know so little about the environment in which Homo sapiens evolved that explaining specific traits as an adaption to that environment becomes highly speculative.  Evolutionary psychologists respond that they do know many things about this environment, including the facts that present day humans' ancestors were hunter-gatherers, that they generally lived in small tribes, etc.  Edward Hagen argues that the human past environments were not radically different in the same sense as the Carboniferous or Jurassic periods and that the animal and plant taxa of the era were similar to those of the modern world, as was the geology and ecology. Hagen argues that few would deny that other organs evolved in the EEA (for example, lungs evolving in an oxygen rich atmopshere) yet critics question whether or not the brain's EEA is truly knowable, which he argues constitutes selective scepticism. Hagen also argues that most evolutionary psychology research is based on the fact that females can get pregnant and males cannot, which Hagen observes was also true in the EEA.  
John Alcock describes this as the "No Time Machine Argument", as critics are arguing that since it is not possible to travel back in time to the EEA, then it cannot be determined what was going on there and thus what was adaptive. Alcock argues that present day evidence allows researchers to be reasonably confident about the conditions of the EEA and that the fact that so many human behaviours are adaptive in the current environment is evidence that the ancestral environment of humans had much in common with the present one, as these behaviours would have evolved in the ancestral environment. Thus Alcock concludes that researchers can make predictions on the adaptive value of traits.  Similarly, Dominic Murphy argues that alternative explanations cannot just be forwarded but instead need their own evidence and predictions - if one explanation makes predictions that the others cannot, it is reasonable to have confidence in that explanation. In addition, Murphy argues that other historical sciences also make predictions about modern phenomena to come up with explanations about past phenomena, for example cosmologists look for evidence for what we would expect to see in the modern day if the Big Bang was true, while geologists make predictions about modern phenomena to determine if an asteroid wiped out the dinosaurs. Murphy argues that if other historical disciplines can conduct tests without a time machine, then the onus is on the critics to show why evolutionary psychology is untestable if other historical disciplines are not, as "methods should be judged across the board, not singled out for ridicule in one context." 
Modularity of mind Edit
Evolutionary psychologists generally presume that, like the body, the mind is made up of many evolved modular adaptations,  although there is some disagreement within the discipline regarding the degree of general plasticity, or "generality," of some modules.  It has been suggested that modularity evolves because, compared to non-modular networks, it would have conferred an advantage in terms of fitness  and because connection costs are lower. 
In contrast, some academics argue that it is unnecessary to posit the existence of highly domain specific modules, and, suggest that the neural anatomy of the brain supports a model based on more domain general faculties and processes.   Moreover, empirical support for the domain-specific theory stems almost entirely from performance on variations of the Wason selection task which is extremely limited in scope as it only tests one subtype of deductive reasoning.  
Cultural rather than genetic development of cognitive tools Edit
Cecilia Heyes has argued that the picture presented by some evolutionary psychology of the human mind as a collection of cognitive instincts – organs of thought shaped by genetic evolution over very long time periods   – does not fit research results. She posits instead that humans have cognitive gadgets – "special-purpose organs of thought" built in the course of development through social interaction. Similar criticisms are articulated by Subrena E. Smith of the University of New Hampshire.   
Response by evolutionary psychologists Edit
Evolutionary psychologists have addressed many of their critics (see, for example, books by Segerstråle (2000), Defenders of the Truth: The Battle for Science in the Sociobiology Debate and Beyond,  Barkow (2005), Missing the Revolution: Darwinism for Social Scientists,  and Alcock (2001), The Triumph of Sociobiology  ). Among their rebuttals are that some criticisms are straw men, are based on an incorrect nature versus nurture dichotomy, are based on misunderstandings of the discipline, etc.          Robert Kurzban suggested that ". critics of the field, when they err, are not slightly missing the mark. Their confusion is deep and profound. It's not like they are marksmen who can't quite hit the center of the target they're holding the gun backwards." 
Background and Context
Family patterns are constantly changing, along with the rest of society. The very idea of parenthood as an involved intimate relationship to be cherished may be relatively new, or newly rediscovered.3 3 For an overview over ideas about childhood now and in previous centuries, see David Archard, Children: Rights and Childhood (Abingdon: Routledge, 2015), part I.
A more recent development in many parts of the world is that co-parents break up and move apart, then form new families with new partners, all the while remaining active parents to their first children. This often results in more than two adults playing a parent-like role in children’s lives, with ‘bonus’ fathers and mothers, in addition to the typically two original parents. Another development, though not as large in numbers, is that families are intentionally started by other constellations than the two-person romantic couple, for example by single women and by polyamorous groups of three or more adults outside of traditionally patriarchal polygamous contexts.4 4 For various examples of new ways of forming families, see the contributions in Daniela Cutas and Sarah Chan (eds.), Families – Beyond the Nuclear Ideal (Bloomsbury, 2014) For polyamory in particular, see Elisabeth Sheff, The Polyamorists next Door: Inside Multiple-Partner Relationships and Families (Rowman & Littlefield, 2014).
Both of these developments pose challenges to the two-parent presumption.
Critics of the traditional, two-parent family have usually focused their attention on the legal institution of marriage. Some have argued that marriage should be open not only to romantic but to caring relationships more generally,5 5 Elizabeth Brake, Minimizing Marriage: Marriage, Morality, and the Law (Oxford: Oxford University Press, 2012) see also Brake, ‘Equality and non-hierarchy in marriage: What do feminists really want’, in Elizabeth Brake (ed.) After Marriage: Rethinking Marital Relationships (New York: Oxford University Press, 2016), pp. 100–124.
some that it should be replaced by some other institution that supports such broad caring relationships,6 6 Tamara Metz, Untying the Knot: Marriage, the State, and the Case for Their Divorce (Princeton: Princeton University Press, 2010).
some that it should be abolished altogether, either in favor of private contracts or in favor of piecemeal regulation of more particular and concrete relationships not based on legal status, such as cohabitation and co-parenting.7 7 For the piecemeal regulation approach, see Clare Chambers, Against Marriage: An Egalitarian Defence of the Marriage-Free State (Oxford: Oxford University Press 2017), especially chapter 5. On the contract approach, see Chambers (Chapter 4) for a critical overview. One recent endorsement is Ronald Den Otter, In Defense of Plural Marriage (New York: Cambridge University Press, 2015).
Such reform would to some extent undermine the basis for the two-parent presumption as a social and legal norm. However, as I will argue below, the number of parents in a family need not be determined by how parents structure their romantic or caring relationships, or what institutions help them to do so.
Very few philosophical contributions, as far as I know, discuss more specifically the pros and cons of having more than two parents in a family. One notable exception is Daniela Cutas, who considers whether three parents might be better than two and notes several important dimensions, some of which I will expand on.8 8 D. Cutas, ‘On triparenting. Is having three committed parents better than having only Two?’, Journal of Medical Ethics 37, 12 (2011): 735–38.
Mianna Lotz convincingly argues that it should be legally possible to recognise gamete donors and surrogate mothers as parents, in addition to the recipient or commissioning parents.9 9 Mianna Lotz, ‘The two-parent limitation in ART parentage law: Old-fashioned law for new-fashioned families’, in Cutas and Chan, op. cit., pp. 34–48 see also Melanie B. Jacobs, ‘Why just two – disaggregating traditional parental rights and responsibilities to recognize multiple parents’, Journal of Law & Family Studies 9 (2007): 309–39.
Samantha Brennan and Bill Cameron similarly consider whether various existing family constellations with more than two people in a parenting role should be legally recognised.10 10 Samantha Brennan and Bill Cameron, ‘How many parents can a child have? Philosophical reflections on the ‘three parent case,’ Dialogue: Canadian Philosophical Review / Revue Canadienne de Philosophie 54, 1 (2015): 45–61.
They continue this discussion in a separate article claiming that families should be centered around children and parenting, rather than romance.11 11 Samantha Brennan and Bill Cameron, ‘Is marriage bad for children? Rethinking the connection between romantic love, having a child, and marriage’, in Elizabeth Brake (ed.) After Marriage: Rethinking Marital Relationships, (Oxford University Press, 2016), pp. 84–99.
All of these authors mainly defend the viability of currently existing alternative family constellations with more (or fewer) than two parents. Lotz especially bases her arguments on the advantages of legally recognising the relationships people are now engaged in without legal support.
In some contrast to this important perspective, I investigate what number of parents is best for families, in particular for those not already committed to some number, including future children and future parents. I allow myself to discuss this issue in the abstract, somewhat removed from current practice and current laws and norms, in order to consider what practice, laws, and norms would be best in a more long-term perspective. For this reason, I don’t consider social stigma an important dimension. Certainly, a child today with five parents, in most places in the world, would be disadvantaged by other people’s suspicion, misunderstanding, or even hostility. However, if five parents would be best for this child, absent this disadvantage, that is a reason to fight such unfounded and oppressive norms.
We have demonstrated how allele age estimates can provide insight to a range of problems in statistical and population genetics. However, there are several important assumptions and limitations of the approach. First, a key assumption is that of a single origin for each allele. Given the size of the human population and the mutation rate, it is likely that every allele has arisen multiple times over evolutionary history. Yet, unless the mutation rate is extremely high, it is still probable that most individuals carrying the allele do so through common ancestry. Moreover, multiple origins can potentially be identified through the presence of the allele on multiple haplotype backgrounds, as has, for example, been seen for the rs4988235 variant at LCT  (though we note that a previous study  concluded that the allele of variant rs4988235 was brought into African populations through historic gene flow, possibly through the Roman Empire), the O blood group , or alleles in the Human Leukocyte Antigene (HLA) region . A variant lying in a region with high rates of noncrossover (gene conversion) may similarly be found on multiple haplotype backgrounds . However, for genomes with very high mutation rates, such as HIV-1 , recurrence is sufficiently high to make estimates of allele age meaningless. In addition, while we have shown GEVA to be robust to realistic levels of sequencing and haplotype phasing error, the actual structures of error found in reference data sources, such as the TGP, have additional complexity whose effect is unknown .
Our approach also assumes a known and time-invariant rate of recombination. For most species, only indirect estimates of the per-generation recombination rate are available, and in humans  and mice , there is evidence for evolution in the fine-scale location of recombination hotspots through changes in the binding preferences of PRDM9 (PR domain zinc finger protein 9). However, because broad-scale recombination rates evolve at a much lower rate than hotspot location  and because our approach for detecting recombination events is driven largely by the presence of recombinant haplotypes, we expect GEVA to be relatively robust for recent variants. Older variants may be more affected, but for such variants, most information comes from the mutation clock, which is likely to have been more stable over time.
We have shown that the ages of variants are highly correlated when estimated separately in independent samples, which agrees with the assumption that, for the majority of alleles, mutations occurred only once in the history of the population, such that the true age of an allele refers to a fixed point in time. In principle, the age can be estimated irrespective of the frequency distribution observed in different study cohorts. Our results show substantial heterogeneity in the relationship between frequency and age, revealing the impact of often unknown demographic variables on the distribution of alleles within and across different ancestry groups, which may further be confounded by the mode and strength of selection on particular alleles. The estimation profiles of variants shown in Fig 3 provide only a few examples of cases in which the frequency may not be reliable as a proxy for the age. Our method and the Atlas of Variant Age may therefore provide more robust measures for analyses that otherwise rely on population or sample-specific allele frequencies.
The Atlas of Variant Age also has multiple applications beyond statistical and population genetics. For example, recent variants provide a natural index when searching for related samples in population-scale data sets. We have demonstrated how variant age information can be leveraged more comprehensively, using a nonparametric approach, to learn about genealogical history, relatedness between individuals, and ancestral connections between populations. Our approach to infer coalescent profiles (pairwise CCF and sample-wide CIF) captures ancestry proportions and coalescence rate variations as a function of time, from which we can distinguish recent from past demographic effects or estimate changes of relative relatedness over time. As illustrated for whole-genome sequencing data from the TGP and SGDP, our methodology accesses a time dimension to study relatedness between individual genomes and among entire sample cohorts. Applications to other data sets may use information from the Atlas of Variant Age without the need to re-estimate ages, thus demonstrating the value of this resource for exploratory data analysis.
Finally, as presented here, it is possible to combine information from multiple, potentially even distributed data sets by estimating coalescent time distributions for pairs of concordant and discordant haplotypes in each data resource separately or to update age estimates by the inclusion of additional samples. Estimation of the age of particular variants may gain additional accuracy by increasing the number of pairwise comparisons, depending on the history of the allele and the genealogical resolution attainable from the diversity of ancestral backgrounds inherent to available sample data. Future studies may reveal new variants, particularly within under-represented ancestry groups, that can also be added to the Atlas of Variant Age. The methods are also applicable to nonhuman species as long as estimates of mutation rate, recombination rate, and generation time are available. Future extensions to infer location of origin or the ancestral haplotype, integrating the growing wealth of genome data from ancient samples, will be an important step towards reconstructing the ancestral history of the entire species.
Alternation of generations
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Alternation of generations, also called metagenesis or heterogenesis, in biology, the alternation of a sexual phase and an asexual phase in the life cycle of an organism. The two phases, or generations, are often morphologically, and sometimes chromosomally, distinct.
In algae, fungi, and plants, alternation of generations is common. It is not always easy to observe, however, since one or the other of the generations is often very small, even microscopic. The sexual phase, called the gametophyte generation, produces gametes, or sex cells, and the asexual phase, or sporophyte generation, produces spores asexually. In terms of chromosomes, the gametophyte is haploid (has a single set of chromosomes), and the sporophyte is diploid (has a double set). In bryophytes, such as mosses and liverworts, the gametophyte is the dominant life phase, whereas in angiosperms and gymnosperms the sporophyte is dominant. The haploid phase is also dominant among fungi. Although some algae have determinate life cycle stages, many species alternate between the sexual and asexual phases in response to environmental conditions.
You are Number One on the Pedigree Chart
The Pedigree or Ancestral Chart is a summary of your family at a glance. It contains basic information about each maternal and paternal generation of your family. Whether you are just beginning your family history or reviewing your research, your pedigree chart is the guide to your family tree.
For beginners, it is helpful to print and complete the form(s) manually before entering the data in a genealogy software program. Filling out the form uniformly will enhance your research and save time later. Sample forms for a four-generation chart are available here.
MyHeritage is offering 2 free weeks of access to their extensive collection of 12 billion historical records, as well as their matching technology that instantly connects you with new information about your ancestors. Sign up using the link below to find out what you can uncover about your family.
Write all the names in their natural sequence First, Middle, SURNAME and title, if any. Example: Samuel J. JONES, Jr.
Some good rules to follow are:
Surnames can be written in all CAPITAL letters.
Always use maiden surnames for women.
Nicknames can be shown in quotation marks or in the notes.
When the surname spelling varies within families or in various years, enter both names with a slash between the names. Example Samuel J. JONES/JONAS
Handwritten dates should be shown as Day, Month, Year without punctuation. Example 05 Jan 1850
The day and year are written in numbers without punctuation. Abbreviate the month to three letters: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
On handwritten ancestral forms, it may be preferable to spell out the month of June to avoid confusion with January.
Always show all four numbers of the year. When your family tree includes history from several centuries, you will be glad you did. Computer programs can be pre-set so that when entered, they convert automatically to the selected format.
Using Date Abbreviations
When a date is estimated or speculative, it is prefaced by abt (about) or ca (circa, meaning around.) The ‘c’ is not capitalized. This abbreviation can be confused with CA, the postal abbreviation for the state of California.
Begin with the smallest identifying information and continue to the largest, separating entries with commas to show the divisions Example: Chicago, Cook, IL. It is not necessary to repeat the word County. If only the county is known, write it as Cook County, IL.
The space for ‘country’ can be left blank. When all or most of your entries are in the United States, identify all other countries.
Numbering the Handwritten Chart
1. YOU are #1, whether male or female. If married, enter your spouse’s name in the space provided. Complete a separate Pedigree Chart for the spouse where he or she will be #1.
2. Your FATHER is person #2. Paternal entries are shown on the upper line of each generation. Each male generation number is multiplied by 2 and they always have even numbers.
3. Your MOTHER is person #3. Maternal entries are on the lower lines. Each female generation number is multiplied by 2 and then by adding one. They always have odd numbers.
Some computer genealogy software programs may be unnumbered or they may assign numbers automatically which do not agree with the manual numbering system described in this lesson. Review the software help section to determine if the numbering system can be shown or modified.
Regardless of the numbering system you choose or use, the Pedigree Chart will be your map to the past.
The Things We Carry: What Our Ancestors Didn't Tell Us
What if your maverick blood sugar, your obstinate obesity, the asthma that has plagued you throughout your life, or the nightmares from which you wake numb and shaking, are not the result of your own lived experience, but are instead manifestations of hidden or unspoken traumas bequeathed from past generations? What if what happened to your great-grandparents has shaped who you are through a mix of external circumstances and epigenetic expression?
In the old Darwinian understanding of genetic inheritance, evolution was thought to be a gradual process that occurred over eons as a species evolved to adapt to a changed environment. On his trip to the Galapagos Islands in 1835, Darwin observed several species of finches. He speculated that the birds probably originated from the same ancestor finch and wondered what could now account for the slight variation among the birds. He noticed that the beaks of the ground-dwelling nut eaters were uniquely suited for their predominant food source, nuts, while the tree-dwelling insect-eating finches had slightly different beaks. From this observation, he postulated that spontaneous mutation accounted for the difference in finch beaks and that a process of natural selection allowed for the mutant birds to thrive.
In The Epigenetics Revolution: How Modern Biology Is Rewriting Our Understanding of Genetics, Disease, and Inheritance, Nessa Carey, a molecular biologist, writes that our understanding of DNA based on Mendelian and Darwinian principles, and the work of Watson and Crick, cannot sufficiently explain rapid changes in species that occur in a single generation. As she sees it, epigenetics is revolutionizing how we understand biology. Whenever two genetically identical individuals are non-identical in some way we can measure, epigenetics is at play.
Take, for example, identical twins who have the same DNA code. In childhood, they appear to be identical, but as they age and are subject to different environmental and emotional conditions, they may lose their look-alikeness and develop different physical characteristics and medical conditions. Let’s say both twins carry a genetic mutation that predisposes a person to get breast cancer. How do we explain only one twin getting the disease? If DNA were completely responsible for shaping a person, we would expect the twins to be identical in every way, including which heritable diseases they get. This isn’t what necessarily occurs. Epigenetics explains changes in gene activity and expression not dependent on our DNA sequence.
Epigenetics is one way to explain the connection between nature and nurture, or as Carey puts it, “how the environment talks to us and alters us, sometimes forever.” The process of epigenetics changes the chemical modifications surrounding and attaching to our genetic material that in turn changes the way genes are switched on or off without altering the genes themselves.
I was drawn to epigenetics while doing research on transgenerational trauma for my second novel which explores how the hidden or suppressed stories within a family line can shape future generations. In my own life, I couldn’t account for the dread that would sometimes descend on me for no apparent reason. It seemed to me there was something vaster, more amorphous and inexplicable at work than the usual psychological culprits. I needed to understand what it was. I began to wonder if the darkness I carried had its source in the suffering of unknown ancestors whose history of banishment and exile was in my blood.
Epigenetics offered some answers.
In a landmark epidemiological study that investigated the effect of famine in pregnant Dutch women during The Hunger Winter, from November 1944 through the spring of 1945, researchers found that a mother’s starvation affected the birth weights of children who had been in the womb during that difficult period. The children of mothers who were malnourished during their first trimester had children with higher rates of obesity in later years. The traumatic stress in the wombs of the Dutch mothers during The Hunger Winter somehow transferred effects to the children, grandchildren and even the great-grandchildren of the original mothers.
In the relatively new field of behavioral epigenetics, Holocaust studies and research have studied the physiological and psychological effects of genocide, ethnic cleansing, and other overwhelming emotional experiences such as occur from natural disasters, rape, the loss of a child, or an abusive home situation. Their findings have documented that trauma can affect the expression or suppression of certain genes, not only for the person involved but also for succeeding generations.
In a recent talk on NPR, the award-winning author Jacqueline Woodson raises the question of “ancestral memory” in the descendants of Africans slaves who crossed the Atlantic in slave ships under horrific conditions. Could the prevalence of high blood pressure among African-Americans today be an epigenetic response to the trauma experienced by the slaves who survived the voyage from Africa? Woodson speaks of her fear of swimming in large bodies of water, attributing this fear, which she shares with other African-Americans, to a set of behaviors loosely defined as “The Middle Passage Syndrome.”
What about the effects of familial shame, guilt, despair, rage, hopelessness? Can these be passed on to descendants? Evidence points to the affirmative. Silence, concealment, denial, dissociation are ways individuals and families cope with overwhelming experiences. Many of us are raised with the dictums: It’s water under the bridge. The past is the past. Don’t talk about it. Unfortunately, what is unthinkable or unmentionable does not disappear from our psyches. While the horror may be suppressed in the victim and even her offspring, third and fourth generations often feel “haunted” by something they can’t name. Nightmares, depression, anxiety, and somatic metaphors that stand for the initial trauma resurrect the historical suffering in new forms.
In her book, The Ancestor Syndrome: Transgenerational Psychotherapy and the Hidden Links in the Family Tree, French psychotherapist Anne Ancelin Schützenberger describes a patient she calls “the butterfly chaser.” The case offers a fascinating instance of how ancestral traumas can influence and shape an individual who has no knowledge of them:
“The patient was a geology lover. Every Sunday he went out looking for stones, collecting them and breaking them. He also chased butterflies, caught them and stuffed them in a jar of cyanide before pinning them up.”
Distraught with his life, the man went for counseling. His analyst decided to investigate the man’s family, going back several generations. What the analyst learned was that the patient had a grandfather who nobody mentioned and who was a secret. The doctor convinced the patient to find out more about the grandfather. In doing so, the troubled patient discovered that his mother’s father had done “shameful things.” Among other unlawful deeds, he was suspected of being a bank robber and was sent into forced labor, in French, casser les cailloux, which means, “to break rocks.” Later, the grandfather was executed in the gas chamber. The rock-breaking, butterfly-gassing grandson had known none of this.
Schützenberger continues: “In a certain number of cases, pastimes, hobbies or leisure activities which can derive from family secrets, are surprisingly full of meaning.” Her book was written in 1998, before knowledge of epigenetics, but she writes: “strange behavior, illness or delirium” are often the result of these inherited “ghosts” who are half-buried in our unconscious, like a secret buried alive.
However, we are more than our ghosts, more than the composite of our memories, inherited or otherwise. In The Developing Genome: An Introduction to Behavioral Epigenetics, developmental cognitive neuroscientist David S. Moore cautions against viewing epigenetics as “fetal programming.” Writing about the effects of abusive parenting on subsequent generations, he finds recent research encouraging: “The possibility that these sorts of patterns reflect epigenetic effects is exciting because epigenetic effects are potentially reversible, either through interventions with specific drugs or through treatment programs that provide other experiences.”
What might these other experiences be? To this point, Jungian analyst James Hollis, in his book Hauntings: Dispelling the Ghosts Who Run Our Lives, asks: “How do we exorcise the haunting of our separate histories? How do we see outside the lens ground for us by fate…?”
His answer aims to inspire creativity. “The difference between us and the mill horse is our capacity for imagination,” he writes, reminding us that our neuroses keep us stuck in old patterns. Our complexes “can only replay the old events, scripts, and moribund outcomes of their origin.”
In suggesting we look to our imaginations as a portal to healing, Hollis leads us back to the ancient arts of ceremony and ritual, and to our in-dwelling creative spirits that remain alive no matter what terrible thing has happened to us. Here might be the way, exclusive of therapy and medication, to re-imagine and remember who we are beyond our traumas. We are our own best shamans, capable of connecting to those divine forces that lie outside our ego’s tunneled and sometimes tortured vision.
Healing trauma involves movement, intrapsychic and literal. If trauma freezes us to a spot in time, a place-memory, and to inherited patterns of behavior, so self-expression in the form of creative ceremony—dancing, singing, sculpting—inspires new energies to flow. Pick up your drum! Dance under the moon! Start a journal. Transformation begins with following your brave heart into the unknown.
Dale Kushner is the author of the novel, The Conditions of Love. She wrote about her decision to become a novelist rather than a Jungian therapist in her first post for Psychology Today, “Treating Patients, Creating Characters.” If you enjoyed this post, you may also be interested in “My Childhood Trauma: What I Learned, What You Need to Know,” "How Facing Our Shadow Can Release Us from Scapegoating," “Dreaming Our Lives: 5 Things Our Dreams Could Be Telling Us,” and “Mothers, Witches, and the Power of Archetypes.” Keep up with Dale by liking her Facebook page. Read more from Dale on her blog.
Examples of F1 Generation
A Monohybrid Cross
When the “Father of Genetics”, Gregor Mendel, was first unfolding the secrets of pea genetics, he started by producing lines of pure-breeding peas. Peas are a variety of plant which can self-fertilize, meaning the male part of the plant can fertilize the eggs produced by the female part of the plant. When allowed to self-fertilize, these plants would produce offspring with the same traits. For example, the pea pods on one plant and all its offspring would produce green pods, while another plant would produce all yellow pods. To unlock the secrets of how these traits were passed to offspring, Mendel decided to cross these two lines of plants. Mendel took the pollen from yellow-pod plants and transferred it to green-pod plants. He then did the opposite cross, of green-pod pollen to yellow-pod flowers.
Scientist now designate these original two plants as the parental generation or simply the P generation. Once fertilized, the parental generation grows peas, which contain the genetic information for the first generation of offspring, or the F1 generation. Mendel planted these peas and noticed a curious fact about the color of the pea pods they produced: they were all green! The yellow-pod plants had contributed genetically to the F1 generation, but only green-pods were found.
Mendel had to do one further experiment to determine what was happening with the genetics controlling pod color. Mendel took a plant from the F1 generation, and allowed that plant to self-fertilize. He then planted and observed the offspring from this cross. Because it is a cross of the offspring, it represents the second filial generation, or F2 generation. Mendel observed that the F2 generation contained a mixture of green and yellow pods. Mendel showed that the 3:1 ratio of yellow-pod to green-pod plants could only be obtainable if both parents carried a copy of both the yellow and green alleles, and that the yellow allele had to be dominant over green.
Modern scientists now describe the cross of Mendel’s F1 generation as a monohybrid cross. The individuals in the cross all had one allele for green pods and one allele for yellow pods, making them hybrids. This cross only examined one trait, however many more traits can be observed at once.
A Test Cross
In a test cross, we take our unknown dominant seed, grow it into a plant, and fertilize it with a plant grown from a green seed. We know that green peas must contain two recessive alleles (yy). Therefore, one of two things can happen. We know that the yellow-pea plant has at least one dominant allele, but we don’t know what the other allele could be. The offspring of this cross, the F1 generation, can have two outcomes. Either the seeds will be all yellow, or they will be half yellow and half green. All yellow seeds in the F1 generation means that the unidentified seed we started with had two dominant alleles (YY). Only this could mask the green alleles present in the other parent. If the F1 generation produces a half and half mix, we know that the other allele in the parental yellow seed had to be a recessive allele, and that the parental yellow-pea plant is a hybrid.
1. Two pea plants are crossed. Both are homozygous for the genes controlling flower color. One produces purple flowers, while the other produces white flowers. What is the ratio of offspring in the F1 generation if the purple allele is dominant?
A. 1:1 Purple to White
B. All White
C. All Purple
2. You are a scientist studying a new species of fish. It is found that the fish come in two varieties, blue and red. Through other experiments, scientists have determined that red is dominant. You have a red fish, and you want to know if he is homozygous or heterozygous for the trait. What should you do?
A. A Test Cross
B. Breed with other red fish
C. Cross your fingers
3. A scientist is breeding daisies and studying their traits. He takes two plants to begin his experiments with. He collects their seeds, and grows the plants. He then crosses these plants with each other and collects the seeds they create. These seeds are again grown, crossed, and the seeds collected. This final round of seeds is planted and grows into plants. What generation do these plants represent?
A. F1 Generation
B. F5 Generation
C. F4 Generation
The science of epigenetic inheritance of the effects of trauma is young, which means it is still generating heated debate
There are other known kinds of epigenetic mechanisms that are relatively little studied. One of them is called histone modification, where the proteins that act as a scaffold for DNA are chemically tagged. Now research is starting to suggest that histones could also be involved in epigenetic inheritance through the generations in mammals.
“I suspect the answer is that all of these mechanisms could interact to give us the phenomenon that is intergenerational inheritance of acquired traits,” says Dias.
The science of epigenetic inheritance of the effects of trauma is young, which means it is still generating heated debate. For Yehuda, who did pioneering work on Post-Traumatic Stress Disorder in the 1990s, this comes with a sense of déjà vu.
Exactly how trauma is passed down through the generations is still unclear as the mechanisms that act on the DNA are not fully understood (Credit: Alamy/Getty Images/BBC)
“Where we are with epigenetics today feels like how it was when we first started doing research into PTSD,” she says. “It was a controversial diagnosis. Not everyone believed there could be long term effect of trauma.”
Nearly 30 years later, PTSD is a medically accepted condition that explains why the legacy of trauma can span decades in a person’s lifetime.
But if trauma is shown to be passed down the generations in humans in the same way as it appears to be in mice, we shouldn’t feel a sense of inevitability about this inheritance, says Dias.
Using his cherry blossom experiments in mice, he tested what would happen if males that feared the scent were later desensitised to the smell. The mice were repeatedly exposed to the scent without receiving a foot shock.
“The mouse hasn’t forgotten, but a new association is being formed now this odour is no longer paired with the foot shock,” says Dias.
When he looked at their sperm, they had lost their characteristic “fearful” epigenetic signature after the desensitisation process. The pups of these mice also no longer showed the heightened sensitivity to the scent. So, it if a mouse “unlearns” the association of a scent and pain, then the next generation may escape the effects.
It also suggests that if humans inherit trauma in similar ways, the effect on our DNA could be undone using techniques like cognitive behavioural therapy.
“There’s a malleability to the system,” says Dias. “The die is not cast. For the most part, we are not messed up as a human race, even though trauma abounds in our environment.”
At least in some cases, Dias says, healing the effects of trauma in our lifetimes can put a stop to it echoing further down the generations.
The artworks in this article were created by Javier Hirschfeld for the BBC.