Last updated on March 15, 2014 at 1:24 EDT

Spotting Venomous Snakes Played Major Role in Human Evolution

July 31, 2006



Isbell suggests instead that primates developed good close-up eyesight to avoid a dangerous predator — the snake.

“A snake is the only predator you really need to see close up. If it’s a long way away it’s not dangerous,” Isbell said.

Neurological studies by others show that the structure of the brain’s visual system does not actually fit with the idea that vision evolved along with reaching and grasping, Isbell said. But the visual system does seem to be well connected to the “fear module,” brain structures involved in vigilance, fear and learning.



“There’s an evolutionary arms race between the predators and prey. Primates get better at spotting and avoiding snakes, so the snakes get better at concealment, or more venomous, and the primates respond,” Isbell said.

Some primate groups less threatened by snakes show fewer signs of evolutionary pressure to evolve better vision. For example, the lemurs of Madagascar do not have any venomous snakes in their environment, and in evolutionary terms “have stayed where they are,” Isbell said. In South America, monkeys arrived millions of years before venomous snakes, and show less specialization in their visual system compared with Old World monkeys and apes, which all have good vision, including color.



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