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Tuesday, November 5, 2013

Primates are super fast snake spotters

Primates are surprisingly quick to identify snakes. Now we know why. Scientists led by Quan Van Le of the University of Toyama have discovered neurons that respond specifically to snake images.

The researchers used two macaque monkeys that had been born in captivity and had never seen a snake. The monkeys were shown color photographs of snakes, monkey faces (angry or neutral), monkey hands, or simple shapes (circle, square, cross or star). Scientists were able to record how strongly neurons within a specific part of the monkeys’ brains (the medial and dorsolateral pulvinar, a region that only exists in primates) responded to those images.

Of 91 neurons tested, 37 responded more strongly to snake images than to any of the other photographs. The next biggest response was for face images, to which 26 neurons had the strongest response. I find this amazing. Think about how strongly we humans react to images of the human face. Not only do we see faces everywhere, in mountain sides, cheese sandwiches, the surface of Mars, but we are also exquisitely programmed to read the details of expression and nuance in those faces. Yet, some primates have a stronger visual reaction to snakes than to the faces of their fellow monkeys!

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This suggests that for our primate ancestors, spotting a snake was a better survival skill than noticing when a group member was pissed off at you. The comparison between snakes and faces hasn’t been made in humans, though other studies have shown that we humans pick out snakes more quickly than other stimuli. This probably means that, over the course of evolutionary history, snakes have been one of the most dangerous things a primate was likely to encounter during its lifetime.

Van Le Q, Isbell LA, Matsumoto J, Nguyen M, Hori E, Maior RS, Tomaz C, Tran AH, Ono T, & Nishijo H (2013). Pulvinar neurons reveal neurobiological evidence of past selection for rapid detection of snakes. Proceedings of the National Academy of Sciences of the United States of America PMID: 24167268.