Bluejay writes:
Spider bites can be annoying and painful, and so it makes sense for humans to develop behavioral aversions to them. But, to claim an evolutionary significance for arachnophobia requires spiders to have had a significant impact on human fitness, and I just don't see that as plausible.
- The Old World, where humans evolved, doesn't have any spiders that are known to have killed people, and only a handful that are known to cause significant health effects, although these are so uncommonly encountered by humans that bites are almost never reported.
- In Asia, where the most dangerous Old World spiders occur, people regularly eat spiders, so I don't see arachnophobia being a major component of human evolution there.
- The only spiders known to have caused fatalities (only four taxa) are native to Australia and the Americas.
The best explanation for arachnophobia is as a learned or cultural behavior. But, I have no idea about the causes and explanations for ophidiophobia (fear of snakes).
Thank you for sharing your knowledge of spiders. I assume you are referring to extant species. While your evidence is suggestive, it doesn’t rule out the possibility that our ancestors encountered more dangerous species that are now extinct. In fact, it is possible that a genetic predisposition to learn to fear spiders and snakes started with mammalian ancestors that predated the first primates.
While the facts you mention cast doubt on the evolutionary threat hypothesis, there is a fair amount of empirical evidence on the other side of the issue. In
a recent study, Vanessa LoBue of Rutgers University writes:
Evidence of a predisposition to learn to fear evolutionary threats comes from experiments with rhesus monkeys and human adults. Research with laboratory-reared rhesus monkeys has shown that they selectively learn to fear stimuli such as snakes from observing a conspecific after very few trials. Furthermore, research with human adults has shown superior conditioning of skin conductance responses when participants are conditioned to associate an electric shock with spider and snake stimuli compared with neutral stimuli (see
hman & Mineka, 2001, for a review). Together, this research provides evidence supporting the idea that both human adults and non-human primates learn more quickly to fear evolutionary threats than neutral stimuli.
LoBue’s paper provides the first evidence of enhanced visual detection of spiders in young children. She writes:
In a series of experiments, preschoolers and adults were asked to find the single spider picture among an array of eight mushrooms or cockroaches or the reverse. Both children and adults detected the presence of spiders more rapidly than both categories of distracter stimuli. Furthermore, there was no difference between the detection of two neutral stimuli (cockroaches vs. mushrooms).
A previous study in preschoolers showed similar results for snakes. Although it is possible that there were cultural influences on the preschoolers, these studies suggest a genetic predisposition because the researchers were measuring visual attention, not fear, and because even people who did not fear spiders or snakes showed greater visual attention to those putative evolutionary threats.