Do snakes send shivers down your spine? With their sinuous shapes and fairly unpredictable movements, snakes often evoke a primal fear in humans, and it's a fear that scientists suggest helped the brains of our ancestors evolve into what they are now, according to Science magazine.
New research from the University of Toyama in Japan and the University of Brasilia in Brazil supports the older theory that snakes helped the ancient primate brain become hard-wired to avoid them, via our enlarged visual centers that help us pick out specific features of the world (like a snake's camoflauged body) and forward-facing eyes, as an encounter with a venomous snake could have lead to an untimely death for our ancestors.
Lynne Isbell, a behavioral ecologist the University of California, Davis, who published her "Snake Detection Theory" in 2006, told Science magazine that snakes were "the first and most persistent predators" of early mammals. According to her theory, other mammals that contended with snakes were burrowing creatures that didn't rely heavily on vision, while primates had to develop special visual detection strategies in order to avoid them.
To test her controversial theory, neuroscientists from the University of Toyama and the University of Brasilia contacted Isbell in hopes that she would help collect find neuroscientific evidence. By studying the brains of monkeys, the team discovered the way that images of snakes affect "the pulvinar-a cluster of neurons in an evolutionarily ancient part of the brain called the thalamus," believed to direct our attention to a potential threat. Primates have much larger pulvinars than other animals, and certain parts of the pulvinars are unique to them.
The research team inserted electrodes into the brains of two captive-born macaque monkeys who had never encountered snakes before and measured the electrical spikes "from individual neurons in two regions of the pulvinar while the primates looked at four types of images: snakes both coiled and elongated, macaque faces with both angry and neutral expressions, macaque hands in various positions, and geometric shapes such as circles and stars," according to Science magazine.
The macaque monkeys the fastest and stronger reactions when shown the images of the snakes, 40 percent of the 91 neurons that became activated during the experiment deemed "snake-best." These neurons also fired frequently when the highly social monkeys saw angry faces, though images of snakes were the most triggering, even though these monkeys had never encountered snakes.
These results suggest that our brains have built-in mechanisms for recognizing important and potentially dangerous shapes found in nature.
The latest research, published online in Proceedings of the National Academy of Sciences, is, according to Isbell, the "first neuroscientific support" for her Snake Detection Theory.
