Our ancestors may have eaten each other's brains, infact cannibalism and Prion Disease may have been rampant in ancient humans as Elizabeth Pennisi wrote in her commentary (Science, Apr 11, 227-228, 2003). A team of researchers led by John Collinge of University College in London suggests that cannibalism may have caused epidemics of kuru and Creutzfeld Jacob disease, which can be spread by eating contaminated flesh. Natural selection would then have favored people with mutations, allowing them to survive and reproduce. Those two diseases and the human form of mad cow disease are believed to be caused by prions, an abnormal protein that can cause proteins to clump in the brain. The British research team reported that protective genes, selected through polymorphisms, are mutant versions of the prion protein gene and show signs of having spread among the population by the means of natural selection. The prion disease has provided the selection pressure to widespread the protective gene polymorphisms among humans.
John Whitfield in Nature News (see Our ancestors had brains – for dinner, April, 11, 2003, still online on May) resumes an article (Mead, S. et al. Balancing selection at the prion protein gene consistent with prehistoric kurulike epidemcis. Science, published online, doi:10.1126/science.1083320, 2003) on a terrible and fascinating subject which is dedicated the book The Trembling Mountain: a personal account of Kuru, Cannibals and Mad Cow Disease, written by Robert Klitzman, M.D. (amazon).