Spider-sense? Humans have it
What's the dim figure lurking in the corner? Yikes, a spider! A new study suggests that humans have a special spider-sense that makes us exquisitely attuned to the crawling critters, even when we're paying no attention to our surroundings.
Such spider-specific vigilance makes sense, because early humans and Homo sapiens evolved in Africa in the company of highly poisonous spiders, says the study's lead author. One bite can incapacitate victims for days – leaving them vulnerable to other dangers – and can even cause death. So a talent for noticing spiders may have been advantageous eons ago, even if it isn't now.
To test whether humans have a special eye for spiders, the scientists recruited college students to perform a simple task: look at lines shown on a computer monitor and choose the longest. After the subjects had performed the task three times, they were asked to do it again. This time, in addition to the lines, another object flashed on the screen. It appeared for just 200 milliseconds, about as much time as the blink of an eye.
If the object shown were a picture of a hypodermic needle, less than 15 percent of subjects were able to notice it, pinpoint its location on the computer screen, and identify it. The line-categorizing task had absorbed them so thoroughly that their attention wasn't easily diverted. Similarly, only 10 percent noticed, located and identified an image of a housefly.
But more than half noticed, located and identified a picture of a spider, says evolutionary psychologist Joshua New of Barnard College. Many also noticed and identified a stylized spider image consisting of a blob with four straight lines running through it to represent four pairs of legs.
"A central body plus radiating segments – that's the template you need to (turn on) this super-responsive awareness," New says. His study will appear in an upcoming issue of Evolution and Human Behavior. "If you're walking around and there's a spider on the ground and a needle, you'd be be more likely to step on the needle than on the spider" – despite the unpleasant memories most people have of getting shots.
The study is well done, says developmental psychologist Vanessa LoBue of Rutgers University, who was not an author of a new paper. She says it's clear that spiders claim special attention from humans, but she's "not convinced" that we're quick to notice spiders because they were a threat to our ancestors.
New responds that his research ruled out reasons other than an evolutionary explanation for our acute spider vision. For example, if people noticed spiders because they'd learned to fear them, research subjects with a terror of spiders should have detected the spiders more readily than subjects without arachnophobia. That wasn't true, indicating primal wariness of spiders rather than a newly acquired fear.