The most comprehensive study to date exploring the genetic divergence of humans and chimpanzees has revealed that the genes most favoured by natural selection are those associated with immunity, tumour suppression, and programmed cell death.These genes show signs of positive natural selection in both branches of the evolutionary tree and are changing more swiftly than would be expected through random mutation alone. Lead scientist Rasmus Nielsen and colleagues at the University of Copenhagen, Denmark, examined the 13,731 chimp genes that have equivalent genes with known functions in humans. Research in 2003 revealed that genes involved with smell, hearing, digestion, long bone growth, and hairiness are undergoing positive natural selection in chimps and humans. The new study has found that the strongest evidence for selection is related to disease defence and apoptosis - or programmed cell death - which is linked to sperm production.
