If blue eyes are regressive (overridden by brown eyes) then, how could millions of north Europeans end up with blue eyes, supposing that blue eyes come from a single mutation?
In: Biology
Even if an entire generation, or several generations were not to have brown eyes, the recessive gene would remain in the gene pool and could come up again. It’s likely that the first ever human that had blue eyes didn’t have any blue eye children, or even grand children. It probably took multiple generations of breeding within a community, or several communities before the gene became common enough that another blue eyed child was born.
From an evolutionary standpoint there was something about the people with blue eyes that made them successful and made a lot of children spreading that particular gene. Even if it was a case that they just happened to survive a particular catastrophe leading to the blue eyed descendants being more common place.
For all the people with blue eyes, there’s a lot more people with the recessive gene.
If human dating and paring were truly random, then blue eyes would be a lot less common and would be at risk of going extinct, but pairing is **not** random.
People do tend to date people with similar ethnic background, so the chances of a pairing of people with the recessive gene is higher than it would be if dating were random. Asian people for example make up more than half of the overall population. So if Europeans dated randomly they would be far more likely to date an asian person that is highly unlikely to have the gene so the gene would become less common. But while European + Asian pairings are somewhat common, European + European pairings are far more likely if you get the point.
The blue eye gene is now so common in the European population, that even if you have brown eyes, depending on the ethnic background of you and your partner, there can be a reasonable chance that you can have children with blue eyes.
Blue eyes are also considered desirable by a lot of people, so that can encourage people to date people with blue eyes to pass on that gene. If it was undesirable it would be less likely to be passed on.
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