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Janet Fang 08 Apr 2015, 12:50

Why spiders? Why couldn't it be "follow the butterflies"? For some, the fear of spiders is innate and not learned. According to a duo of psychologists, spiders are an evolutionarily-persistent ancestral hazard that humans are especially attuned to -- even when we’re not paying particular attention to anything else in our surroundings. After all, our ancestors in Africa co-existed with the eight-legged crawlies for millions of years, and being aware of spiders with potentially killer bites was critical for survival. The findings were published in Evolution and Human Behavior last year. 

Our visual system may have retained “ancestral mechanisms” dedicated to the quick detection of immediate and specific threats that have persisted throughout evolutionary time, according to Barnard College’s Joshua New and Tamsin German from the University of California, Santa Barbara. These are the snakes, spiders, and angry faces of our nightmares. Amber fossil specimens of Steatoda, the sister genus to our cosmopolitan widow spiders (Latrodectus, which are particularly dense in southern Africa), have been dated to 40 million years. But while having a “biological preparedness” for recognizing angry human faces is still useful in today’s society, spiders aren't as serious of a threat these days, compared to the deep past. Only about 200 out of 40,000 pose serious medical concerns for healthy adults, with about 200 confirmed fatalities a year worldwide. 

So, to test this one ancestral hazard, the duo recruited hundreds of college students for a simple task: Pick the longer of the two lines in a cross that’s displayed on a computer screen. After the participants completed this trial a few times, the researchers added an object that flashed for a few hundred milliseconds across the screen. These blink-and-you’ll-miss-it objects ranged from modern threats (hypodermic needles) to fear-irrelevant creatures (houseflies) to ancestral hazards (spiders). 

Less than 15 percent noticed, identified, and could pinpoint the location of the hypodermic needle in these "inattentional blindness" tests. Similarly, only 10 percent successfully located the housefly, USA Today reports -- they were too absorbed in the task to divert their attention. However, when a spider or spidery shape quickly flashed on the screen, more than half of the participants were able to identify and locate which quadrant it appeared in.  

"A central body plus radiating segments -- that's the template you need to (turn on) this super-responsive awareness," New tells USA Today. "If you're walking around and there's a spider on the ground and a needle, you'd be more likely to step on the needle than on the spider." And that’s despite any unpleasant memories we might have of getting shots.

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