Snakes Helped Evolution Of High-Quality Vision
October 29, 2013

Fear Of Snakes May Have Triggered Evolution Of Close-Range Vision

[ Watch the Video: What Do Snakes Have To Do With Vision Evolution? ]

redOrbit Staff & Wire Reports - Your Universe Online

Neuroscientists from Brazil and Japan have found new evidence in support of a theory that that human ancestors developed high-quality vision as a defense mechanism against the threat of snakes.

The study, which was published Monday in the journal Proceedings of the National Academy of Sciences, demonstrated that there are specific nerve cells located in the brains of rhesus macaque monkeys that respond to pictures of the slithering serpents.

That finding supports a theory originally put forward by University of California, Davis anthropology professor Lynne Isbell in 2006. In her study, Isbell hypothesized that our primate ancestors had evolved the ability to see well at close-range largely to locate and avoid dangerous snakes.

Working with colleagues from Toyama University and the University of Brasilia, her work analyzing rhesus macaque monkeys has found that the neurons that were sensitive to the snake images were more numerous than other nerve cells. They also had a stronger, quicker response than those firing in response to images of macaque faces or geometric figures. Isbell said the fact that primates are social in nature made the findings somewhat surprising.

“We're finding results consistent with the idea that snakes have exerted strong selective pressure on primates,” she explained. Both mammals and snakes that were large enough to consume them evolved at roughly the same time, approximately 100 million years ago. Venomous serpents are believed to have first appeared 40 million years later, sharing the trees and grasslands with primates, the study authors noted.

Working in the laboratory of professor Hisao Nishijo, the researchers analyzed the neural mechanisms that govern fear and other emotions in rhesus macaque monkeys – especially those that occur instinctively, without learning or memory.

Previous experts have used snakes to provoke fear in monkeys, and Nishijo believed that Isbell’s theory could explain what makes monkeys so afraid of snakes. Their research was an international collaboration under the Asian Core Program of the Japan Society for the Promotion of Science.

“The results show that the brain has special neural circuits to detect snakes, and this suggests that the neural circuits to detect snakes have been genetically encoded,” Nishijo said. The monkeys used in the experiment were raised in a walled colony, and had no previous experience with a real snake, the researchers said.

“I don't see another way to explain the sensitivity of these neurons to snakes except through an evolutionary path,” Isbell added, stating that she was happy to be working with neuroscientists on the project. “I don't do neuroscience and they don't do evolution, but we can put our brains together and I think it brings a wider perspective to neuroscience and new insights for evolution.”