Brown eyes?

Question

Why don't we all have brown eyes by now? As we know from school education the gene that make us have brown eyes is dominent over green and blue. Surely after this amount of generations since we evolved we would have practically eliminated blue and green eyes. And further more if we evolved from apes why do we even have blue and green eyes, apes only have brown eyes?

Answer 1

Here comes a long post but this answers it from an anthropological and scientific stand point.

People all originally came from hot East Africa (Ethiopia is where the oldest human fossils have been found and is the land between the Tigris and Euphrates---whether you approach the origin of human beings from a Biblical standpoint or one that is based on the fossil record) .
When they populated the world and spread out eye color, and physical features began to change to adapt to climates. Brown eyed people are originally from sunny environments because the dark pigment in the eye protects them from the sun. Likewise, people native to hot to warm environments have darker skin colors (from olive to very dark brown) because melanin contains antioxidants, inhibits the loss of collagen from UVA/UVB rays, and prevents excess vitamin D from forming by blocking sun rays.
Light colored eyes (blue, green, and grey) are recessive because Europe (like Australia) was the last place on earth to be populated by human beings. Consider this, when some people first left Africa or migrated out, they spread to the Middle East (still warm-kept the dark eyes, tan skin, dark hair) , throughout the Meditteranean, then they went to modern day Russia where (indigenous Russians have dark eyes, slightly lighter skin, dark hair). Later people went to Asia where it was both warm and cold because of the sun exposure they still needed melanin and the dark color in their eyes for sun protection. Skin color may have lightened to adjust to colder climates to promoted vitamin D absorption or it may have remained dark (if you live in more tropical regions of Asia).
Lastly, people spread to Europe because thousands of years ago, Europe was covered in Ice like Antartica is today. People with dark eyes, dark hair, dark skin could not survive the cold and went snow blind, limbs and extremities snapped off, and people either died because their skin could not make vitamin D. People who's genes mutated or changed to suit the environment survived. Blue, green, and grey eyes reflect the bright light from the snow and whiter skin promoted vitamin D absorption. Lighter hair also resulted from a change in diet, from great amounts of protein to reduced amounts of protein.
This change could have occurred over a few hundred years or a few millenia.

But long story short, the world is predominantly a warm place.
Warm weather= brown eyes and more melanin in hair and skin, as seen in the majority of the world's population.

Cold weather, climate= most places in the world (except Northern Europe, Antartican, Alaska) are not cold. So the people who live there have lighter skin/ eyes/ hair and are less abundant.

* Note, the only reason scientists believe that the Inuit survived the cold climates of North America is because they eat A WHOLE LOT of protein from fish, etc.. There fore their skin did not have to lighten to promote vitamin D absorption. ANd the snow did not bother their eyes because of their rich diet, they wore alot of furs to cover their faces, and they have beneficial folds near their eyelids to protect their eyes from the harsh, bitter winds.

One can expect if the world continues to get hotter then the frequency of melanin enriched people will increase even more. Versus if the world suddenly got ice cold and every continent experienced an Ice Age, humans with low levels of melanin would increase in frequency and those with dark eyes/skin/ hair would greatly decrease. Human beings like animals have to respond to environmental pressures and only those who can survive actually live and produce offspring (whether by being genetically compatible with the environment, technological advancements, or mutation) ..

Answer 2

Here the thing... unless there's some force acting to favour one trait over another, the amounts of genes in the pool generally remain constant.

So, yes. Brown eyes is dominant. But a brown-eyed person will often have blue-eyed genes. Those genes don't go away just because they aren't being expressed. They can be passed on to children, so it's possible for two brown-eyed parents to have a blue-eyed child, if the genes are right.

So unless something massive happens, there will ALWAYS be blue-eyed and green-eyed genes in the population, and more or less random mixing will cause blue-eyed and green-eyed people to keep springing up too!

As to your second question about why humans would have coloured eyes and not apes... there's an interesting study that was conducted in that regard (link 1 - be patient... it loads slowly). These scientists theorized that having colored eyes against a light background would make it much easier to see what a person was looking at, so they tested to see if apes and human babies looked at where a person's head or eyes were pointing. They found that apes paid almost no attention to the eyes themselves, while even human babies paid almost exclusive attention to them. This demonstrates at least that humans at apes are looking at different things in such situations.

And it may suggest an answer to your question. Apes have dark and hairier faces, so a subtle difference such as eye colour is much less likely to stand out. On the other hand, the humans with the whitest skin (Scandinavians and the like) are most likely to have coloured eyes. So apes (and perhaps even dark-skinned humans) may not have developed this trait because it doesn't really do them much good.

Personally, I could stand a lot more evidence before I settle on that as a final answer, but it certainly seems like a very plausible first guess.

Incidentally, if that theory is true, then it would suggest that there's a selective pressure that ENCOURAGES coloured eyes... at least in light-skinned people. If this is so, then rather than brown-eyed people taking over the world, I would expect blue and green-eyed people to, as the browns all eventually dropped out of the population.

Answer 3

The blue eyes gene phenotype does not have any disadvantages when it comes to survival. If having blue eyes made you more visible to predators and more likely to be eaten....then less homozygous individuals (2 blue genes/blue eyes) would survive, and thus there would be fewer offspring to pass the gene on to. The Homozygous brown individuals or heterozygous individuals (those with brown eyes) would proliferate, and pass on their genes. Eventually homozygous blue individuals who actually have blue eyes would disappear as only the "fittest survive". The blue gene would still exist in heterozygous individuals, but their phenotype would be brown eyes, they would be blue gene "carriers". Just in the same way that if you have both copies of the cystic fibrosis gene in the past you would have probably not lived past 20 years old....probably not reproduced and thus not passed on the gene. These days as medicine gets better and people live longer...the natural selection pressure "survival of the fittest" is less important....as the not so "fit" people are surviving, thus recessive genes/mutated genes that confer some kind of "malfunction" which in the past would have "marked you out for death" as it were.....stay in the gene pool longer.

Just to correct the post 1 above mine.......the area between the rivers Tigris and Euphrates is NOT Ethiopia. Both rivers have their sources in Turkey, and run down through present day Iraq to the Persian gulf. The area was known historically as Mesopotamia or Babylon

Answer 4

Research has shown that many people tend to go for partners who have some of the qualities people think are nice in themselves.
Lots of people regard eyes as high on their lists of attractive traits that they look for in a partner.
So if they like their own big blue eyes mabe they will find big blue eyes attractive in a partner?

Also my mum has brown eyes and my dad has blue eyes, out of 3 children my older sister is the only one who ended up with brown eyes...

Answer 5

for me it depends in the girl. Like I might notice a girl with black hair as well as think she is totally hot however see a girl with blond curly hair that is meh and vice versa.

Answer 6

ok heres the thing. brown may be dominant, but there are also heterozygous genes. ur dad and mom may have brown eyes, but if ur grandparents had green/blue eyes, u may get heritage from this part. ( Gg + Gg = GG, Gg, Gg, gg). so we dont really eliminate those eye colours.
and im not sure if all apes had brown eyes, but remember that mutations occur.

Answer 7

because theres always the gene in us. no matter how faint it is its still there. my teacher taught me this (i hope it makes sense):

take a pack of cards, and separate them into pairs, you'll definitely get at least one group with 2red cards. remove all those cards and shuffle, separate them into pairs. again remove all the double reds. if you continue to do this, the number of double red sets decreases, but the red cards are still there

just because the colour is recessive, its still passed down through generations, even if its not used. there will always be the possibility that your decent line can have green or blue eyes, even if your family hasnt had them for many generations. its all to do with the random gene that the foetus gets. just because certain genes are more dominant doesnt mean that the recessive ones are non-existant.
hope i helped and made sense..

Answer 8

Dominance and frequency are not the same. To understand why recessive genes might still be very common in a population, look up the phrase 'Hardy-Weinberg equilibrium'

Answer 9

I was born together with blonde hair so i think i actually look fine thats the way i was born

Answer 10

variety is the spice of life