"An evolutionary arms race between early snakes and mammals triggered the development of improved vision and large brains in primates, a radical new theory suggests.

The idea, proposed by Lynne Isbell, an anthropologist at the University of California, Davis, suggests that snakes and primates share a long and intimate history, one that forced both groups to evolve new strategies as each attempted to gain the upper hand."

http://news.yahoo.com/s/space/20060721/sc_space/fearofsnakesdroveprimateevolutionscientistsays