We "naked apes" aren't as hirsute as our primate cousins. We still have an ape-like density of hair follicles—but we sprout out peach fuzz, instead of a thick coat. Those downy hairs may be more than an evolutionary leftover, though. They may be "hair-trigger" sensors for bedbugs and other parasites. So says a study in the journal Biology Letters. [Isabelle Dean and Michael T. Siva-Jothy, Human fine body hair enhances ectoparasite detection, link to come.]
Researchers shaved one forearm on each of 29 student volunteers, and placed a hungry bedbug there. Without looking, the students counted each time they felt something. The researchers repeated the experiment on each victim's unshaven arm as a control. And don't worry—in each case they plucked off bedbugs just as they prepared to dine.
Turns out students were significantly more likely to sense bedbugs crawling on their unshaven arms. And those tangles of hair slowed down the bug's search for a place to snack, too. The authors say our fine human hair may thus be perfectly evolved: thin enough to eliminate hiding spots for bugs, but thick enough to act as an alarm system for bloodsuckers in the night—enough to make anyone's hair stand on end.
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