juvenissun
... and God saw that it was good.
- Apr 5, 2007
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In the case of white tigers, it is a single mutation. But take a real case like skin pigmentation in humans. Lighter skin has been selected for as humans have moved away from the tropics, and multiple mutations in multiple genes have spread in the population. In fact, different genes were involved in Asia and in Europe (with some overlap).
In this kind of situation, there's no reason at all that the same mutation would have to occur in different individuals. (Sometimes it does happen, e.g. the sickle cell mutation has occurred multiple times, as has the mutation conferring lactose tolerance.) Instead, one person has one mutation that makes skin somewhat lighter. That's selected for and spreads in his descendants. Someone else, at a different time, has a different mutation in another gene that also makes skin somewhat lighter. That one spreads through her descendants. Eventually, some individuals inherit both new variants, and their skin is even lighter and their descendants do even better than those with the single mutation.
So the exact same mutation could take place in multiple people of different lineage. I would say this must be driven by the same environmental factors.
So, we have this situation:
Environment A --> drives mutation A --> make individuals fits better to environment A --> the mutation A gets higher frequency.
I guess it should be correct.
If so, why would the original population be a problem? What is the difference between 1 individual and 1000 individuals at the very beginning? As long as the environment is stable, the frequency will steadily increase anyway.
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