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As we saw in the last blog post, the theoretical basis for evolutionary psychology is compelling. But is this a just-so story to explain entomophobia or might there be empirical evidence? Recall that the strong view of evolutionary psychology is that our fears are innate—we do not need to learn avoidance of spiders and roaches and bears, oh my (to adapt Dorothy’s short-list of dangers).
Learning is for losers if early humans had to survive a cobra bite to associate snakes with danger. Nor would prehistoric children live long enough to complete home schooling. Our survival depended on obeying genetically engrained, preverbal rules. These inborn commands were overly inclusive for a good reason: avoiding a wad of spider-like hair on the cave floor had nominal costs, while grasping a vine-like snake in the jungle was disastrous.
So, what is the evidence for genetically encoded fear? Scientists have found a heritable disposition of emotionality and we might also inherit a nonspecific tendency to be fearful. Other researchers argue for a stronger position—that we inherit particular classes of fear. Research has shown that the heritability of animal fears is 47 percent (the highest such heritability is seen with agoraphobia at 67 percent). And twin studies, which allow scientists to isolate genetic and environmental factors, reveal that specific phobias are perhaps the only psychological disorder for which there is compelling evidence of a direct, genetic contribution. Animal fears are particularly prone to run in families.
Experimental data also support the possibility that we are hard wired for fear. People consistently overestimate the likelihood that fear-relevant stimuli (e.g., an image of a spider) will be associated with a painful experience (e.g., an electric shock) compared to neutral stimuli. More compellingly, a fearful response may not even require awareness of the aversive creature. When subjects were presented with various images for just 30 milliseconds (faster than the blink of an eye), arachnophobes showed a marked change in skin conductance indicating fear.
However, we’re not genetically imprinted with a detailed bestiary. The sinuous shape of a snake—rather than the details of any particular serpent—is crucial to our rapid detection of these legless animals. As for 6- and 8-legged dangers, young mammals, including humans, keenly attend to characteristics such as skittering movements. We attend to key features of whatever can harm us.
Psychologists have found that fear of motionless insects and spiders is also triggered by visual cues (the ‘ugliness’ of antennae projecting from the head and the oddly proportioned eyes and bodies) to which we add tactile features (the discomfort of hairiness and sliminess). It seems that the more divergent a creature is from the human form, the greater its capacity to evoke fear. And this sense of alien life, with all of its symbolic and imaginative implications, has spawned some nightmarish literature and film, as we’ll see in the next blog entry.
