Was humanity born in the mother of all plagues?

Around 100,000 years ago, the human race was on the brink of extinction. Confined to Africa, our population had fallen to less than 10,000. Yet within a few tens of thousands of years, we began spreading around the world.

New genetic evidence suggests that one factor contributing to the population bottleneck was a massive epidemic of bacterial disease. The bacteria were exploiting two immune system genes, turning them against us. So the solution was simple: get rid of the traitorous genes.

Ajit Varki of the University of California, San Diego and colleagues looked at two genes called Siglec-13 and Siglec-17. Both code for proteins that are involved in controlling the immune system, helping to decide whether immune cells should go on the offensive.

Varki found that both genes are active in chimpanzees, but not in humans. Siglec-13 has been entirely deleted from the human genome, while Siglec-17 is non-functional as a result of losing one letter from its code. Read More...