Here‘s interesting research on the propensity of humans and other primates to spot snakes, even sneaky ones. Apparently, there’s a Snake Detection Theory that says that our vision has evolved to discern camouflaged but dangerous animals, particularly snakes. To test the Snake Detection Theory, researchers in Japan processed photos of various animals so that they were progressively more blurred; in this way, they could compare how much clarity was needed before research subjects could identify the animal. The other animals were supposedly nonthreatening ones, such as cats and birds. (Not everyone agrees!) They found that people saw snakes in photos that were blurrier than the ones in which they first recognized other animals.
Assuming that the images were truly equivalent, this result bolsters the Snake Detection Theory. And this suggests that, in the evolutionary past, our ancestors lived with individuals who didn’t have this snake-seeing facility and thus died of snakebites before reproducing and passing on their genes.