Chimpanzees are about twice as diverse as humans. Humans have had an effective population size of something like 15,000. The census size for both species was almost certainly larger, but there’s nothing wrong with 50,000 as an estimate.[quote=“Mark_Moore, post:114, topic:37468”]
To preserve naturalism, they should be somewhat spaced out. How long does it take a new gene- not just a variant of an existing gene but a new gene, to spread from one individual to EVERY individual in a population of that size when they have long generations and low fertility rates?
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With no selective benefit, it takes on average 4 times the effective population size for a new genetic variant to reach fixation – call it 60,000 generations for ancestral humans. What you seem to be missing, though, is that is also takes the same amount of time for 10 variants, or a hundred or a hundred thousand, to reach fixation. Millions of genetic variants and thousands of new genes (most but not all duplicates of existing genes) are circulating at any given time, and some of them drift to fixation. In a constant-sized population, the rate at which variants fix is the rate at which new mutations occur in a single individual. So for most of our ancestral history, something like forty mutations would have fixed every generation.
So why do you think it would take too much time? How many new genes do you think are circulating at any one time?