I know that eye color is directly related to the amount of melanin present in the front layers of the iris. But what’s the biological need behind different color?
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There isn’t really a need for it. People with blue eyes have better night vision and worse vision in bright light, because more gets through their iris, but it’s not really needed.
Evolution is kind of random, some traits exist not because they’re useful, but because they’re not harmful enough to be bred out by selection.
High melanin provides better protection from harsh, glaring light. People in bright places may have been better hunter/gatherers as a result, so eyes with melanin were a biologic advantage over eyes without.
But, not all of the Earth is bright, the farther north you go the less of this benefit you see, so eyes without melanin are “about as good” so there isn’t biologic pressure to select for brown eyes.
High melanin provides better protection from harsh, glaring light. People in bright places may have been better hunter/gatherers as a result, so eyes with melanin were a biologic advantage over eyes without.
But, not all of the Earth is bright, the farther north you go the less of this benefit you see, so eyes without melanin are “about as good” so there isn’t biologic pressure to select for brown eyes.
There isn’t really a need for it. People with blue eyes have better night vision and worse vision in bright light, because more gets through their iris, but it’s not really needed.
Evolution is kind of random, some traits exist not because they’re useful, but because they’re not harmful enough to be bred out by selection.
There isn’t always a biological need for diversity, especially in populations like humans where we tend to try to keep everybody alive. Even if your genes deal you a bad hand, your community will likely make sure you don’t die. Needing glasses is a much bigger hit to your survival prospects than eye color, and we fix that. Even blind people have resources available to them.
Basically, a lot of the diversity you see in humans is because differences exist randomly and we don’t let anything kill those people because of it
There isn’t always a biological need for diversity, especially in populations like humans where we tend to try to keep everybody alive. Even if your genes deal you a bad hand, your community will likely make sure you don’t die. Needing glasses is a much bigger hit to your survival prospects than eye color, and we fix that. Even blind people have resources available to them.
Basically, a lot of the diversity you see in humans is because differences exist randomly and we don’t let anything kill those people because of it
There probably isn’t a reason for it. Mutations don’t have to have any advantage in order to become part of our genetic makeup, as long as they don’t have any great disadvantage. Tens of thousands of years ago, someone was probably just born with different colored eyes, and it didn’t make him less likely to survive and pass on those genes, so it became part of the normal range of human eye colors.
There probably isn’t a reason for it. Mutations don’t have to have any advantage in order to become part of our genetic makeup, as long as they don’t have any great disadvantage. Tens of thousands of years ago, someone was probably just born with different colored eyes, and it didn’t make him less likely to survive and pass on those genes, so it became part of the normal range of human eye colors.
Evolutionarily, adaptations don’t arise because they’re necessary. They arise randomly and persist if they, at minimum, don’t significantly interfere with an individual’s ability to have offspring. There’s not significant advantage to any particular eye color, they’re diverse because they don’t really make a difference.
In addition to what everyone else has said, it’s also possible that eye color is a sexually attractive trait. If females of a species are more attracted to certain traits, that trait will increase in the population, regardless of its biological benefit.
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