We humans have two types of Immune-Related GTPase genes, and one of them is called IRGM. These kinds of genes are useful for resisting invading germs like tuberculosis and salmonella. Researchers traced the evolutionary history of these genes within primates, and found out that they used to have many pairs of IRGM genes but eliminated for some unknown reason around 50 million years ago. However, millions of years later in the common ancestor of great apes and humans, the remnants of the gene was active once again and could be translated to produce proteins. Scientists found evidence of a retrovirus insertion in the ancestral genome.The leader of the study, Evan Eichler, said that this "resurrection" occured through a series of complex event, and this tells us that we should not count out a gene until it is fully erased. He also said that the functional plasticity that withstood evolutionary pressures may be useful for fighting infectious agents.
http://www.sciencedaily.com/releases/2009/03/090305204321.htm
