Saturday science subject: Snakes and eyesight

— 5:50 PM on July 22, 2006

An interesting new hypothesis suggests that snakes are to thank for the development of eyesight in primates. Where other mammals gained a better sense of smell and/or immunities to venom in order to not become snake lunch, primates developed their eyesight, University of California Anthropologist Lynne Isbell proposes. She believes snakes are behind these developments in particular because they were one of the first and hardest-to-avoid threats to mammals:

Fossil and DNA evidence suggests that the snakes were already around when the first mammals evolved some 100 million years ago. The reptiles were thus among the first serious predators mammals faced. Today, the only other threats faced by primates are raptors, such as eagles and hawks, and large carnivores, such as bears, large cats and wolves, but these animals evolved long after snakes.

Furthermore, these other predators can be safely detected from a distance. For snakes, the opposite is true.

Primates were in a better place to counteract the threat of snakes via improved eyesight because of their diet, Isbell says. Early primates had a diet rich in sugar from foods like fruit and nectar, which allowed better brain and eyesight development. Other mammals with different diets, meanwhile, had to resort to other methods to ward off snakes. This hypothesis could explain why primates have better color perception than most animals and why their eyes face forward, thus enabling 3D vision, where most other mammals' eyes do not.
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