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144746-146497Even if human misery didn’t start with Adam and Eve, it may have had a thing or two to do with snakes.

Back in 2006, anthropologist Lynne A. Isbell at UC California in Davis noted mammals and snakes’ long, shared evolutionary history, and suggested that snakes may have been mammals’ earliest predators. If so, fear specifically of snakes may have pushed mammalian and, as a result, human brain evolution. Now, evolutionary psychologists at Erasmus University Rotterdam in The Netherlands have tested Isbell’s theory.

The experiment’s subjects: Twenty-four female university students. The routine: Question the women about any snake, spider, or bird fears. Then show them hundreds of pictures of snakes, spiders, and birds, and by EEG measure the strength of immediate and micro-second-later electrical charges generated in the visual systems of their brains. The hypothesis: The neuro-electrical response to pictures of snakes will be stronger than it is for birds or spiders, and may occur so early in the visual recognition process as to be “pre-attentional” or unconscious.

As the researchers expected, on the questionnaire, fear of snakes and of spiders proved to be about equal, and both outranked fear of birds. The data on immediate (and supposedly pre-attentional) electrical activity showed a far stronger reaction to pictures of snakes than to pictures of either spiders or birds. However, the data on micro-second-later electrical activity was fuzzy.

In their report’s analysis, the researchers explained that the later-stage electrical activity was probably at least partly conscious, and therefore may have been disturbed by the women’s learning and thoughts. And so it was to the consistently strong and almost instantaneous electrical response that they drew attention. It showed that, regardless of whether a women professed a fear of snakes, she registered one.

Did snakes play an outsized role in human brain evolution? The Erasmus University Rotterdam team is now (2014) preparing a poster on an even newer study comparing electrical responses to pictures of snakes with responses to pictures of other reptiles. Once again, the snake data slither to an impressive win, suggesting that avoiding snakes entirely may have been a pressing ancestral imperative.


Lynne A. Isbell, “Snakes as agents of evolutionary change in primate brains,” Journal of Human Evolution, 51 (2006) 1e35.  http://www.cnah.org/pdf_files/546.pdf 

J.W. Van Strien, R. Eijlers, I.H.A. Franken, J. Huijding, “Snake pictures draw more early attention than spider pictures in non-phobic women: Evidence from event-related brain potentials,” Biological PsychiatryIn press, available online December 27, 2013. http://www.ncbi.nlm.nih.gov/pubmed/24374241(link is external)

J.W. Van Strien, I.H.A. Franken, J. Huijding, “Early posterior negativity is larger for snake pictures than for other reptile pictures.” Unpublished poster.