Saturday, March 17, 2012

Why Are We Not Hairy Like Other Apes?

We humans are dubbed the "naked apes" because, well, obviously not many of us have hairs all over our body. If evolution is true, we should be hairy like bonobos, no?
Darwin said our ancestors discarded coarser hairs since it's warm like sauna out there on the savannah. And he suggested that we looked sexier without the hair covering our sexual features. Seriously though I can't imagine getting turned on by primates.

Contrary to popular belief, we aren't entirely naked. We do have hairs covering our body, and they are called the vellus hair. And we do have the same density of body hair as other apes of our size.
In a study published in Biology Letters last year, Isabelle Dean and Michael T. Siva-Jothy from the University of Sheffield, UK wrote that fine body hair improves our detection of parasites.
They recruited 29 university students through Facebook, aged between 19 and 27 years for the experiment. Each participant had one of their arms shaved. The researchers then drew a rectangle of Vaseline on both their forearms, and while the volunteers looked away, the duo placed a bed bug within the rectangles.
Dean and Siva-Jothy found out that the participants took longer time to detect the presence of bed bugs on their shaved arm. Also, vellus hair made it harder for the bugs to find an ideal spot to suck on. On unshaved arms, the parasites took between 22 and 26 seconds to find a good place, compared to just 18-19 seconds on shaved arms.

The results showed that fine hair helped us to avoid falling prey to parasites. The researchers further highlighted that other blood-sucking parasites prefer to bite hairless sites on bats and the featherless areas of birds.
So now you know why mosquitoes always bite you at the relatively hairless underside of wrists and ankles.

info: Dean. I, Siva-Jothy. M. T. , Biology Letters, Human fine body hair enhances ectoparasite detection. doi: 10.1098/rsbl.2011.0987

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