Natural selection in humans

This isn't the first time natural selection has been observed in humans. Sickle-cell anemia, for example, displays a classic Hardy-Weinberg equilibrium. What we have here is a large-scale change – an inversion of a portion of a chromosome.

The rearrangement, a 900-kilobase inversion polymorphism, appears in two distinct lineages, H1 and H2, that have diverged for as long as 3 million years with no evidence of having recombined. The H2 lineage—which is rare in Africans, almost nonexistent in East Asians, but found in 20% of Europeans—appears to undergo positive selection in Iceland, with carrier females having 3.2% more children per generation and higher recombination rates.

And:

The extensive divergence between the lineages suggests their separation predated anatomically modern Homo sapiens and potentially even the genus Homo. Stefansson and colleagues suggest the H2 lineage was introduced into the ancestral human gene pool in Africa from species such as Homo heidelbergensis or Homo erectus. But Arcadi Navarro of the Universitat Pompeu Fabra in Barcelona, who did not participate in this study, said he wasn't so sure that was the case. "It does seem very unlikely that this polymorphism has been sitting for 3 million years, half the span of time between humanity's split with chimpanzees," he told The Scientist. "This estimate for the time of convergence was obtained under the assumption of divergence without the influence of selection. If selection has acted here, as very much seems to be the case, maybe the divergence time is not that long. Maybe selection has been acting within each rearrangement."