In an interesting discovery, it seems that early humans on their way out from Africa were interbreeding with other humanoid species that were alive at the time (dead would have made it a been a bit hard to breed). As a result of this interbreeding, our immune-response was increased as other species’ genes were assimilated in to our own.
In a presentation at a discussion on human evolution earlier this month, Peter Parham of Stanford University in California, discussed his investigation in to human leukocyte antigens (HLAs), a family of about 200 essential genes for our immune system.
These HLAs also contains some of the most variable human genes, meaning we’re able to fight off a large number of infectious diseases, and adapt to fight off new ones. While early humans would have had a rather limited set of genes developed for African diseases, Parham presented evidence that showed that interbreeding with the local humanoids resulted in the the adaptation of those genes in to the human genome, and in to that of the Neanderthals.
More can be read here.