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Why aren't green eyes more prevalent, given that the green allele is dominant over the blue one?
My understanding is that human eye colour is determined by two genes:
1) HERC2, with alleles Bx, BB or xx,
2) gey, with alleles GG, Gb or bb,
- B means brown
- x means not brown (this is less confusing than using b for blue here, because having no B allele in HERC2 doesn't necessarily give someone blue eyes; their eyes will be either blue or green depending on the gey gene)
- G means green
- b means blue.
Capital letters stand for alleles that are dominant; lower case, ones that are recessive.
So the 'algorithm' goes:
- 1) look at HERC2; if it's anything other than xx, you've got BROWN eyes
- 2) if HERC2 is xx, look at gey; if it's anything other than bb, you've got GREEN eyes
- 3) still here? then you've got BLUE eyes
My question is this: why is it that green eyes are so rare if the green allele is dominant over the blue one? When a blue-eyed person and a green-eyed person interbreed, their offspring will either be equally likely to have green eyes as blue (if the green-eyed parent is Gb) or always have green (if that parent is GG).
But many more people have blue eyes than green eyes, despite blue being recessive to green.
The obvious answer is that people with blue eyes (xx bb) and people with green eyes (other xx-ers) have tended to avoid breeding with each other to a large extent. Is any other explanation in the ring? Perhaps the greens are catching up?
A gene being dominant does not necessarily imply the gene is also common.
An easy counterexample is Huntington's disease. The gene is dominant, and only one mutant allele of huntingtin would result in development of the disease. However, the allele prevalence of the mutant is low in the general population.
In the absence of a selective advantage of green eyes over blue eyes, the two alleles of the gey gene should remain in genetic equilibrium, and therefore the number of people with green eyes will not increase. In fact, a similar misunderstanding applies to the disappearance of blondes/redheads. In both cases, the allele frequencies will remain unchanged in the absence of selection pressure.
The initial imbalance in the allele frequency could be due to many reasons. Population bottlenecks, genetic drift, and historical selection pressure could all be valid answers.
10 Characteristics of People with Green Eyes
They say you learn an awful lot about a person’s character simply by gazing into their eyes. Some cultures view eyes as being veritable windows to people’s soul and surprisingly enough, there might be some truth to this after all. Scientists now believe that people who share a particular eye color also share certain personality traits.
This might have something to do with how we, as a society, perceive people who look or act a certain way. For instance, green eyes on a woman have always been considered attractive since the days of old and society hasn’t changed that much in that respect. Long story short, here are ten characteristics that most people with green eyes seem to share.
It seems that most people with green eyes are not only good speakers but also good listeners. They seem to be perceptive, attentive, and naturally curious to some extent. In general, people with green eyes are brimming with confidence, a confidence that often arises from their self-belief and spontaneity. It is because of their confidence that they often take an interest in other people’s problems, thinking that they’ll surely be able to help some way.
Most children with green eyes are curious by nature and they often grow up to be just as curious as adults. They seem to want to know about everything, an insatiable desire for knowledge that often transcends into the realm of creativity and ingenuity. As you would expect, people with green eyes will often ask a lot of questions, be it in school or at work, a trait that unfortunately, some people don’t really take kindly to.
We talked about the good and it would only seem fair to point out the bad as well. It is often said that people with green eyes have impulsive behavioral characteristics that make them mischievous and devious. Similar to felines, some would say, they tend to be attractive yet secretive about their intentions, yet another by-product of their impulsive personality. On the bright side, their self-awareness make them pretty humorous, even entertaining to have around.
Green-eyed people do tend to be a bit mystical at times, probably a result of their curious and charismatic personality. This might be why a majority of all mystical beings in movies and pop culture tend to have green eyes, which speaks volumes about how green-eyed people are perceived to this day. It might also have something to do with their self-sufficient nature that often makes them stand out because of their relative independence.
People with green eyes are said to be quite jealous, more jealous than brown-eyed people at least. While people with dark-colored eyes tend to be more permissive by nature, people with bright-colored eye shades are often more passionate, impulsive, and of course, jealous. On a similar note, green-eyed people are masters of passive aggression, as anyone who has ever dated a person with green eyes would tell you. Again, this has everything to do with how society treats green-eyed people and how much this makes them stand out from the rest.
They say green eyes are sparkling like dew in the morning sun. The sheer beauty of bright green eyes is said to capture people’s souls with just a glance, leaving them trapped in a maze of passion and lust. On a more realistic note, this might have something to do with the fact that although green eyes are found in less than 2% of the world’s population, they are the only eye color that changes shades depending on weather and mood. This may be why most poets have attributed passionate characteristics to green-eyed characters, a trait that has transcended into real life over the years. Or maybe it’s the other way around.
Interestingly enough, it seems that most people with green eyes are talented and creative by nature. For instance, you’ll always see green-eyed people having a very novel approach to most situations, along with a very expressive way of dealing with people. These traits arise from their underlying creativity, a type of innovative perspective on things that for some reason, most green-eyed people seem to share.
Maybe as a result of how much of a novelty they are given their rarity, or maybe due to how people treat them throughout their lives, people green eyes always seem to develop a self-absorbed character. To some extent, their self-absorbed nature makes them deceitful and selfish, although not always. It is definitely an argument to be had about nature vs nurture as far as green-eyed people are concerned because they definitely get special treatment in today’s world.
Most green-eyed people seem to be vibrant and cheerful for some reason. Again, due to how much of a novelty they are given their rarity, their presence is always celebrated by those around them, making them feel desired and admired at the same time. In turn, this makes them be lively and vibrant in social situations, or at least that’s how they are conditioned to be. It does seem that most people with green eyes are lovable to some extent, an admiration that reflects their vibrant nature onto the people they surround themselves with.
Apparently, people with green eyes have great analytical skills which when combined with their creative personality make them have a clear outlook on things. As a result, most green-eyed people are witty, well-spoken, and capable of perceiving things that some of us aren’t able to see. It is because of their far-sighted nature and increased perception that they are as successful as they are at school or at work.
Truth About Light Eyes and Light Sensitivity
Dr. Horne explains that photophobia -- the term used to describe light sensitivity -- typically affects people with light eyes because they have less pigmentation in multiple layers of the eye than those with darker eyes. Because of this, they are unable to block out the effects of harsh lights like sunlight and fluorescent lights.
Dr. Horne is careful to note that photophobia refers to light sensitivity, but does not refer to actual permanent loss of vision.
Photophobia may cause a person to have difficulty seeing or focusing in bright lights, or even cause pain around the eyes. So, squinting or rubbing your eyes often when you are in harsh light may be a clear sign that you have some level of photophobia.
Five Traits That Could Get You "Abducted by Aliens"
Are you worried about being abducted by aliens? Many people worldwide have claimed to have been abducted by aliens, been taken against their will to an alien spacecraft or enclosed place, questioned or physically examined, and they remember these experiences either consciously or through methods such as hypnosis. Indeed, many of those people who claim to be 'alien abductees' are seemingly sincere, psychologically healthy, nonpsychotic people—so are their experiences real and their claims to have been abducted true?
Professor Richard McNally and his colleagues at Harvard University have spent over 10 years researching the psychology of alien abductees, and in particular why it is that some people embrace the identity of alien abductee. His research has isolated a number of traits possessed by alien abductees each of which he argues contributes to the experiences they recall when ‘being abducted’ and to the desire to cling on to their belief that aliens were responsible for their abduction experiences. Let’s look at each of these five traits in turn.
1. Regularly experiencing sleep paralysis and hallucinations when awakening: Many people who have reported alien abduction suffer episodes of early morning sleep paralysis. On awakening from this paralysis, their terror gives rise to hallucinations of flashing lights and buzzing sounds. Some experience feelings of ‘floating’ around the room or seeing figures in the room. While many people interpret these post-sleep paralysis experiences as dreaming, some people interpret these experiences as seeing figures, ghosts, or aliens.
2. A tendency to recall false memories: In an elegant set of experimental studies, McNally and colleagues found that individuals who claimed to have been abducted by aliens were prone to what is known as “false memory syndrome." That is, 'alien abductees' regularly claimed to recall words, items, sentences, etc. in memory tests that they had never actually seen before. If this “false memory” effect can be generalized to autobiographical memories, then individuals who claim to have been abducted by aliens would be twice as likely to “falsely remember” things that had never happened to them than would non-abductees.
3. High levels of “absorption”: Alien abductees also score significantly higher than most people on the mental characteristic known as absorption. This is a trait related to fantasy proneness, vivid imagery, and susceptibility to hypnosis and suggestion. Because of this, it is probably not surprising that many alien abductees recall their experiences under hypnosis, where memories of abduction can be induced through suggestibility—especially if the person leading the hypnosis session asks particularly leading questions about abduction.
4. New Age beliefs: Being whisked up into spaceships by tractor beams or light sources is not something that happens every day—nor is it something that is easily explainable within our existing knowledge of physics. Similarly, being subjected to imaginative medical procedures requires a tendency to accept unusual and non-mainstream ideas. This is also a trait possessed by alien abductees. They score highly on measures of magical ideation and endorse New Age ideas that encompass beliefs about alternative medicines and healing, astrology, and fortune telling. Such beliefs would certainly allow the individual to accept things happening to them that would be dismissed by existing scientific knowledge.
5. Familiarity with the cultural narrative of alien abduction: As a cultural phenomenon, alien abduction has entered folklore and the images and descriptions of aliens and their spacecraft have become familiar to many people. Alien abductees tend to be very familiar with this cultural narrative which is one possible reason why their descriptions of aliens and their spaceships are so similar—being fuelled as they are by sci-fi films and numerous books about aliens and alien abduction.
As Professor McNally points out in a very readable review of his studies on alien abduction, it is still unclear whether all these characteristics are necessary ingredients in the recipe for ‘alien abduction’ or whether some are more necessary than others. Other researchers have also identified further traits that appear to be characteristic of ‘alien abductees’, such as paranoid thinking and weak sexual identity. There is still much more research to do to fully understand the motivations and thinking patterns of individuals who claim to have been abducted by aliens, but as McNally shrewdly points out, these people are not anxious nor depressed, they are not psychotic and do not appear to have any obvious mental health problems. ‘Alien abduction’ experiences often deepen spiritual awareness and give shape to the identities of abductees and provide a basis for their beliefs about the world and the universe. Whether the experiences of abduction were real or not, the experiences and interpretations adopted by ‘alien abductees’ are often psychologically helpful and can be spiritually comforting.
Finally, a note of caution. All of these studies of ‘alien abductees’ were carried out after they had their abduction ‘experiences’, so it’s difficult to know whether these five traits are consequences of the experience or were—as McNally suggests—factors that led individuals to interpret rather earthly experiences (such as sleep paralysis and hallucinations) as evidence of abduction. And then—perhaps fantastically—can we genuinely rule out the possibility that such traits are implanted in their victims by aliens in invasive medical procedures carried out on alien space ships! My skeptical, scientific mind says probably not—but who knows?
2 Answers 2
When members of the Reiss family inherit the Founding Titan, they are affected by Karl Fritz's will, and at times, their normally light-colored eyes darken and emit a glow.
However, there seems to be no universal rule outside of the Reiss family. The eye colour aspect seems to be tied in with how it affects memory and will but as far as I can tell there is nothing official/canon so all we can do is speculate.
So here is my speculation:
Inheriting the founding titan and will of another is what changes your eye colour. This explains the Reiss Family as every one of them inherited Karl Fritz's will. But (with only a few extra steps) this also explains Grisha Yaeger.
So after eating Frieda Reiss, clearly Grisha did not inherit her will, instead I think his eye colour change was because of Eren Kruger. Kruger had done some horrible things to Grisha but in his final moments he defected, pushing his comrade off the wall to save Grisha. He then went on to justify all his bad deeds and answer any questions, explaining about the history of the founding titan and King Fritz's goal urging him to help the with the restoration project. He then injected Grisha with the titan serum and allowed himself to be eaten. Grisha did go on to help the cause, starting a family and continuing to investigate the ongoings of Paradise Island. My interpretation is that the moment he ate Frieda was the point of no return, where symbolically he truly inherited Kruger's will and thus his eye colour changed.
To answer your actual question:
Finally we have Eren Yaeger who's eyes remain green throughout. I believe his eyes remain the same colour because of his overwhelmingly powerful determination, ie. even after inheriting the founding titan his will remained his own.
Eye color and eye health
While the rest of us see beauty and wonder in eye color, eye doctors see the source of eye color — the iris — as a signpost for vision problems. Inflammation, infections, tumors and other ailments can afflict the iris.
Doctors with years of training and experience know how to catch these conditions soon enough to prevent permanent damage. This is why regular eye exams repay your investment many times over.
Dominant isn't Always Common
Just because a trait is dominant does not mean it is common. Each color represents different levels of light eyes. Blue=80%+, teal=50-79%, olive=20-49%, brown=1-19%, black=none. Image courtesy of Dark Tichondrias
One of the first things we&rsquore taught in genetics is that some traits are dominant and others are recessive. And that the dominant traits trump the recessive ones.
So brown eyes trump blue eyes. And red hair is always trumped by other hair colors. And so on.
From this, people often jump to the conclusion that the dominant trait is also the most common one. This isn&rsquot always the case and there is no reason it should be.
Whether or not a trait is common has to do with how many copies of that gene version (or allele) are in the population. It has little or nothing to do with whether the trait is dominant or recessive.
Let&rsquos take eye color as an example. The decision on whether to have brown eyes or not is pretty much controlled by a single gene, OCA2.
We can think of OCA2 as having two versions, brown and not-brown. The brown allele of OCA2 is dominant over the not-brown allele.
Nearly everyone in most of Africa has brown eyes. This isn&rsquot because brown eyes are dominant over blue and green. Instead, it is because there are mostly brown alleles of OCA2 in the African population.
Northern Europe is a different story. In some parts of the continent, over 80% of the population has lighter colored eyes. Here the not-brown allele is more common even though it is recessive.
Now this allele isn&rsquot exclusive, there are still brown-eyed folks in northern Europe. So why don&rsquot their brown eyes dominate over time? Because in populations, dominant isn&rsquot dominant over other people&rsquos recessive gene versions. Your brown eyes can&rsquot affect my kids&rsquo eye color unless we get married.
Let&rsquos do a thought experiment to make this clearer. To simplify things we&rsquoll call brown eyes B and not-brown eyes b.
Without some sort of outside pressure, the ratio of blue to brown eyes stays the same.
Remember, you will have brown eyes if you are BB or Bb and blue or green if you are bb. This is because brown (B) is dominant over blue and green (b).
Imagine we start out with eleven bb people and one Bb person. The Bb person has 4 kids with one of the bb folks and each bb couple also has 4 kids.
Using regular old Mendelian genetics, we'll have 20 bb people from our 5 bb couples and 2 Bb and 2 bb from our mixed couple. This is 2 people with brown eyes and 22 people with blue or green. The same ratio as we started with. Brown did not become more common.
Now these folks all pair up randomly and have 4 kids each. Since we aren't going to allow incest, the Bb folks will find a bb for a mate. If they have 4 kids each, then we have 44 bb and 4 Bb. Again the same eleven blue to one brown ratio. Whether an allele is dominant or not does not affect how common a trait is.
Now of course traits can become more common over time. The changes just don&rsquot have anything to do with whether the trait is dominant or not.
If brown eyes gave an advantage, then it would start to become more common. Brown eyes would also become more common if a bunch of Africans moved in or many of the blue-eyed people were killed for some reason (witch burning?). And there are other ways too of getting more brown eyes in Europe. Or more blue eyes in Africa (see South Africa for example).
Dominant does not mean common. Which in some ways is a good thing considering diseases like Huntington&rsquos disease that are dominant.
Everyone's Eyes Are Actually Brown, So Cheers To Never Feeling Special Again
Blue and green eyes are often treasured and admired, not only for their beauty, but for their rarity.
But it turns out everyone actually has brown eyes, according to science.
Yes, you read that correctly. Blue-eyed and green-eyed folks: Your eyes are brown.
Biology and physics are apparently to blame for this.
As Dr. Gary Heiting, a licensed optometrist and senior editor of the eye care website All About Vision, explained to CNN,
Melanin, a pigment also found in skin and hair, is naturally dark brown. It can absorb different amounts of light, depending on how much of it there is.
If there is a lot of melanin in the iris, it absorbs more light and and less light is reflected out, so the iris looks brown.
But if there isn't a lot of melanin in the iris, it reflects more light out.
This process is known as "scattering," and it means the light is reflecting back on shorter wavelengths, which coincides with the blue end of the light color spectrum.
Since babies' eyes aren't fully developed and don't have a lot of melanin, this explains why some infants are born with blue eyes, but eventually develop brown eyes.
If you have blue eyes and are feeling less unique because of all this, you might be comforted by a theory from Professor Hans Eiberg at the University of Copenhagen.
Eiberg's research shows blue eyes are the result of a genetic mutation that occurred around 10,000 years ago.
Before this, all humans had brown eyes, but the mutation left some with less melanin in their eyes.
This could be linked to natural selection and survival of the fittest. In other words, certain people evolved to have blue eyes because it made them more attractive as potential mates.
So, even though we all technically have brown eyes, people with blue eyes are, in a way, more evolved (sexier) human beings.
Eiberg's research also shows that all blue-eyed people share a common ancestor, since people with blue eyes possess nearly the exact same genetic sequence in the part of the DNA that dictates eye color.
They share common DNA, much like relatives do.
Comparatively, brown-eyed people exhibit a great deal of disparity when it comes to the gene that determines eye color.
Simply put: Brown-eyed people aren't nearly as unique and don't all share a common ancestor.
Congrats, blue-eyed folks. You're still cool.
Why eyes look different colors
Humans get their eye color from melanin, the protective pigment that also determines skin and hair shades. Melanin is good at absorbing light, which is especially important for the iris, the function of which is to control how much brightness can enter the eyes. Once it passes through the lenses, the majority of the visible light spectrum goes to the retina, where it’s converted to electrical impulses and translated into images by the brain. The little that isn’t absorbed by the iris is reflected back, producing what we see as eye color.
Now, that color depends on the kind and density of melanin a person is born with. There are two types of the pigment: eumelanin, which produces a rich chocolate brown, and pheomelanin, which renders as amber, green, and hazel. Blue eyes, meanwhile, get their hue from having a relatively small amount of eumelanin. When the pigment is low in stock, it scatters light around the front layer of the iris, causing it to re-emerge are shorter blue wavelengths. This makes blue an example of what is called “structural color,” as opposed to brown and to some extent, green and hazel, which would be defined as a “pigment colors.” It’s in part the same reason the sky is blue—an atmospheric light trick known as the Rayleigh effect.
Green eyes are interesting because they combine light scattering and two kinds of pigment: They hold slightly higher amounts of eumelanin than blue eyes, as well as some pheomelanin. Hazel eyes come from the same combination, but they have more melanin concentrated in the outer top layer of the iris. Red and violet eyes, which are much rarer, come from a minute to complete lack of pigment. In fact, red eyes have no melanin whatsoever, so all we’re seeing is the reflection of the blood vessels. When there’s some pigment, but too little to cause wavelengths to scatter, the red and blue interact to produce a rare violet.
A person with albinism might appear to have red eyes, due to the blood vessels being reflected in the un-pigmented iris. National Institute of Health
Eye Color and Health
Eye color may seem like something that just has to do with your appearance. However, some studies suggest that certain eye colors may increase a person’s risk of certain health conditions.
Research from 2011, for instance, suggests a link between blue eyes and type 1 diabetes. Similarly, a review from 2015 suggests a possible link between eye color and hearing loss. Evidence points to the possibility that people with darker eyes may have a reduced risk of non-age-related hearing loss.
A 2014 study presented at the American Pain Society meeting in 2014 concluded that women with light-colored eyes had a higher reported pain tolerance during pregnancy than those with darker eyes. However, it should be noted that the sample size for this study was relatively small, with a total of 58 women.
A similarly small-sized study of 60 subjects had the same finding when testing pressure pain thresholds and for pain related to cold. However, remember that correlation does not equal causation and more study is needed to prove these effects.