i'm not clear on understanding both maps.. you're just describing the one on the left, correct?

and how did they get 0% for americans if 25-35% of african americans have the allele?

now that i've read the first chapter of that Tomasello and mixingmemory's post i finally understand what the middle Pleistocene is! yay!

the two maps represent two ancestral allele frequencies. 'america' is not the current population, but the indigenous populations. i didn't see any post-1492 populations in the list of populations sampled, so that's why i had to infer african americans rather than state their frequency.

It occurs to me that what we see in Africa is probably not the retention of an ancient gene, but its reemergence after the onset of malaria. A graphic example of the benefits to retaining diversity.