In a new paper published in the journal Primates, author William C. McGrew, a former professor of evolutionary primatology at the University of Cambridge, reports a high rate of venomous snake encounters by his team of primatologists seeking to observe unhabituated wild chimpanzees in Mount Assirik, Senegal, West Africa.

McGrew's snake-encounter analysis in the paper Snakes as hazards: modelling risk by chasing chimpanzees is one test of what's known as the snake-detection theory of primate origins, a set of hypotheses that suggest we (along with other primates) owe certain features of our evolution to the risks posed by death and injury from snakes.

During the 609 days that make up the core period of the analysis, McGrew and his team encountered a snake in Assirik, on average, once every 4.3 days — totaling 132 snake encounters. During the entire study period of four years, 142 snakes of 14 different species were identified. Of these, 64 percent were venomous: 33 cobras, 27 vipers and 24 rear-fanged snakes.