Medusa's Gaze and Vampire's Bite: The Science of Monsters by Matt Kaplan Page A

Bryan Fry at the University of Melbourne and published in Nature in 2006, analyzed large numbers of reptiles and studied the genes associated with their mouth secretions. While doing this, Fry and his colleagues noticed that some lizards had proteins in their mouths that were very similar to those associated with venom in rattlesnakes. This hinted that the common ancestor of lizards and snakes, which lived some one hundred million years ago, may well have already been carrying some mild toxinsin its saliva and that these animals have long presented a threat to primates. 32
    Venomous snakes inhabited many of the landscapes where our ancestors evolved, and their venoms likely had the same effects then that they have on humans today. 33 Such realities are important to recognize, because with two hundred thousand years of cohabitation, there has been a lot of time for evolution to shape the way the primate mind responds to snakes.
    In modern society, where warning signs can be posted in dangerous areas and word of mouth can advise people to be wary of well-known threats, the idea of evolving an intrinsic fear is not easy to grasp. With communication so readily available, we do not need to evolve a fear of things like speeding automobiles and electrocution, since there are plenty of people to tell us it is bad to be hit by a car or shocked by an electrical cable. However, for most living things, warnings are not available, and this would have been the case for our ancestors.
    Imagine a male primate ancestor keen to have a romantic evening with an attractive female. Suppose, eager to impress, the male goes hunting for a rabbit that he can feed to his potential mate. If, while searching for the rabbit, he does not see a coiled viper hidden in the underbrush, his chances of stepping on it are increased. If he does step on it, he is likely to be bitten, and if he dies from the bite, he will not have sex, will not father as many children as males who avoid vipers, and fewer of his genes will be passed along to the next generation.
    Now consider a male who happens to spot the coiled snake, backs away, catches the rabbit (or not), has the romantic evening,and fathers numerous offspring. If the reason for the male noticing the viper had anything to do with genetics, which is possible since genes do code for things like the ability to detect color and motion, then his genes are going to be carried on to his young, who will also be likely to spot hidden snakes. 34
    What all of this means is that there was probably strong evolutionary pressure for our ancestors to be able to notice snakes as immediately dangerous so they could avoid them. And psychological studies seem to support this.
    In a 2001 study conducted by Arne Öhman, a psychologist at the Karolinska Institute in Stockholm, participants were presented with both benign images of flowers and toadstools and threatening images of snakes and spiders. These images were presented nine at a time in a slide show format, and the participants were given a little keypad for each hand. One keypad was to be used if all the images seemed the same, the other was to be used if contrasting images were seen, like benign images standing out from threatening images or threatening images mingled among benign ones. The researchers carefully measured the time between the moment an image was shown and the moment the appropriate button was pushed. Öhman reported in the Journal of Experimental Psychology that students responded much more quickly when snake and spider images appeared than they did when presented with merely benign images. He concluded that modern humans have an innate ability to notice dangerous animals quickly. Moreover, he argued that this innate rapid detection ability came about because evolution has selected for humans whoare able to spot threatening animals and thus not become ill or die before they can reproduce a lot. And he was not alone.
    Numerous studies show that many primate