Tuesday, December 13, 2011

Hairier is better – bedbugs bite our barest bits


This bedbug was caught in the act of needling human skin in the hope of a blood drink during a study of why we have kept a fine covering of fur despite being the nakedest of apes.
We're often reminded that we're genetically almost identical to apes, so how did we become the baldest primate? Charles Darwin thought sexual selection explained it - as he put it, women with less hair were more attractive and men became less hairy as a corollary. Alfred Russell Wallace, who didn't like the idea of sexual selection, attributed our naked form to God. In fact, we have the same density of hair follicles as chimps, it's just our hair is much finer.
So the question becomes, why does fine hair persist in humans?
Now Michael Siva-Jothy and Isabelle Dean of the University of Sheffield, UK, have a suggestion: fine hair helps us detect parasites as they crawl over our bodies. It also makes it harder for the bugs to bite.
The results of their experiments - carried out by putting bedbugs like the one pictured on the arms of student volunteers - suggest that hair lengthens the insect's search for a feeding site, and increases its chances of detection.
"Men have more body hair than women, which is caused by the action of testosterone at puberty," says Siva-Jothy. "This does not necessarily mean that women are more likely to be bitten. Blood-sucking insects are likely to have been selected to prefer to bite hosts in relatively hairless areas."


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