Researchers at the University of California have said that the ability to spot venomous snakes might have played a major role in the evolution of monkeys, apes and humans.
Initial studies suggested that primates developed good vision, enlarged brains, and grasping hands and feet for accomplishing their reaching and grasping functions. These characteristics got evolved as primates started using their hands and eyes to grab insects and other small prey, or to handle and examine fruit and other foods.
But Lynne Isbell, Professor of Anthropology at UC Davis said it was something else. Primates developed good close-up eyesight only for avoiding 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," she said.
Isbell said that neurological studies have also shown that the structure of the brain's visual system does not actually fit with the idea that vision evolved along with reaching and grasping. Vision, she said, was more connected to the "fear module," the brain structure involved with vigilance, fear and learning.
She said fossils and DNA evidence also showed that snakes were the first serious predators of modern mammals, which evolved about 100 million years ago.
"Fossils of snakes with mouths big enough to eat those mammals appear at about the same time. Other animals that could have eaten our ancestors, such as big cats, and hawks and eagles, evolved much later. Venomous snakes evolved about 60 million years ago, raising the stakes and forcing primates to get better at detecting them," she said.
"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," she added.