Why The "Naked Ape" Needs Some Hair

A specially (UV) illuminated bed bug about to plunge its proboscis into the bare waiting skin of a student guinea pig.



Since Desmond Morris' smash book of 1967, The Naked Ape, many people have actually thought of humans....those of us who are members of the primate species Homo sapiens, as "naked apes". The evolutionary arguments for this nakedness, meanwhile, have extended to everything from an intermittent "aquatic period" of several million years" (in which case why didn't we retain some residual gills) to competitive advantages in presenting a healthy skin to a possible mate.

Totally missed in all these ruminations, evidently by Morris as well, is that humans aren't really naked apes at all. Per square centimeter, human skin has as many hair follicles as other great apes - the difference it that they aren't as coarse or wide. So much for fancying that we are some special kind of "angel" or being far beyond those of our cousins, the chimps.

The evolutionary question that emerges then, is why did humans arrive with such fine hair hairs that grows from these abundant follicles. It's obviously not to woo mates, and in fact a majority of human females are not terribly turned on by hirsute males. Nor does there appear to be any kind of benefit in terms of camouflage, or even protection. That poison ivy leaf you touch will still carry a sting and an itch!

Now, two researchers from Britain's Sheffield University - Isabelle Dean and Michael Siva -Jothy- appear to have resolved this conundrum of the purpose of human hair. As published in the recent issue of Biology Letters, their research appears to show these fine human hairs servie as an early warning system to alert us before an arthropod (such as shown in the image) creeping under our covers or sheets puts a hurt on us. The most common threats being bed bugs, as well as certain species of lice. Hence, the fine vellus and terminal hairs are there to warn us - if even slightly disturbed by a small alien beastie attempting to make a meal. In effect, the sensation of the beastie making his way toward his dinner generally awakens us and allows enough time to react before becoming a ready blood meal.

In thier study, the Sheffield researchers recruited 29 university students to act as guinea pigs. Each had a patch of skin on one arm shaved and encompassed by petrleum jelly (to fence the bugs in) and the other arm had a similar patch though unshaven. Subsequently, unfed bed bugs were released to do their thing and the students were requested to look away while the beasties were placed on their arms. Clearly, Siva -Jothy and Dean didn't wish to see their charges freaking out before hand.

These human guniea pigs were then asked to press a button whenever they sensed a critter moving across their skin. Siva -Jothy and Dean found a significant difference in frequencies between the two separate arm patches. When a bug traversed a hairy patch, the button signal was depressed on average every 4 seconds. On a shaved patch more than ten seconds elapsed between detections. Further the bugs perched on the hairy skin took nearly 20% longer to attempt to bite their voluntary hosts. (I say "attempt" because the lab workers removed the bugs before they could sink their proboscises into the waiting flesh).

In all the cases, men (who are hairier) fared better than the female volunteers when the bugs were released onto unshaven patches of skin.

Desmond Morris was indeed correct on observing that human hair had "shrunk" but what he missed out was identifying why it hasn't completely disappeared to render a real naked ape.