We’re not born with a fear of snakes, but it sure seems to develop early.

Now scientists may be closer to a explaining why ophidiophobia ranks among the top fears of humans, and seems to be shared with other primates.

Researchers inserted probes into the brains of Japanese macacques and found that neurons in a part of their brain that controls visual attention were more strongly and quickly activated in response to images of snakes, versus other objects.

The results, published online Monday in the journal Proceedings of the National Academy of Sciences, appear to support a theory that early primates developed advanced perception as an evolutionary response to being prey, not as an adaptation that may have made foraging or hunting easier.