An evolutionary arms race between early snakes (http://www.livescience.com/php/multimedia/imagegallery/igviewer.php?imgid=572&gid=39&index=0) 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 (http://www.livescience.com/evolution/) new strategies as each attempted to gain the upper hand.
To avoid becoming snake food, early mammals had to develop ways to detect and avoid the reptiles (http://www.livescience.com/reptiles/) before they could strike. Some animals evolved better snake sniffers, while others developed immunities to serpent venom when it evolved (http://www.livescience.com/animalworld/051117_lizard_venom.html). Early primates (http://www.livescience.com/monkeys/) developed a better eye for color (http://www.livescience.com/humanbiology/051128_eye_image.html), detail and movement and the ability to see in three dimensions—traits that are important for detecting threats at close range.
Humans are descended from (http://www.livescience.com/humanbiology/top10_missinglinks.html) those same primates.
Scientists had previously thought that these traits evolved together as primates used their hands and eyes to grab insects (http://www.livescience.com/insects/), or pick fruit or to swing through trees, but recent discoveries from neuroscience are casting doubt on these theories.
"Primates went a particular route," Isbell told LiveScience. "They focused on improving their vision to keep away from [snakes]. Other mammals couldn't do that. Primates had the pre-adaptations to go that way."
Harry Greene, an evolutionary biologist and snake expert at Cornell University in New York, says Isbell's new idea is very exciting.
"It strikes me as a very special piece of scholarship and I think it's going to provoke a lot of thought," Greene said.
Isbell's work is detailed in the July issue of the Journal of Human Evolution.