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