Neuroscientists in Brazil and Japan have new evidence to support a theory that we developed high-quality vision as a defense mechanism against the threat of snakes. They looked at the brains of rhesus monkeys and found specific nerve cells that respond to snakes and these neurons were more numerous than other nerve cells. They also had a stronger, quicker response than those firing in response to other images. The monkeys used in the study had grown up in a walled colony and had never been exposed to snakes before suggesting that the sensitivity of these neurons are purely evolutionary. The researchers say that our primate ancestors had evolved the ability to see well at close-range to avoid snakes.