Hairy Back Guys
If you look at some of our relatives, we primates are a fairly hairy bunch.
Primates tend to have all sorts of interesting facial and sometimes even shoulder hair, so humans are not odd in this regard, says anatomist Professor Ian Gibbins from Flinders University.
In fact, Gibbins suspects it wasn't that long ago that we sported a pretty impressive fur coat of our own. The evidence for this comes from .
But evolution is usually pretty prompt at getting rid of features we don't need, says Gibbins, so the reason men still have facial and chest hair is more likely due to sexual selection.
At some stage while we were losing our excess body hair either women found hairy men more attractive, or men preferred non-hairy women.
"The usual argument, " says Gibbins, "is that [sexual selection] is some sort of surrogate for your overall fitness."
"So if you're a good enough feeder or hunter or breeder, or whatever it is, to have enough energy in reserve to make some flashy show then it means you're probably ahead of the pack."
Basically if you're a very hairy man and hairy men are in, you get the girls.
However there are some caveats to this argument.
Firstly, hairiness can vary quite dramatically between different ethnic groups, so to make general statements about male hairiness is fairly difficult. For example, men from a Mediterranean background generally have darker and thicker hair, whereas men of Asian descent often don't have much facial hair at all, says Gibbons.
Secondly, men and women have approximately the same number of hair follicles, what differs is the coarseness of the hairs.
We have two types of hair on our bodies: the coarse, usually pigmented terminal hair which includes our head hair, pubic hair and for men their facial and chest hair; and the finer, less visible vellus hair.
Hair growth and size is modulated by hormones, in particular androgens like testosterone, which kick in during puberty. As men generally have higher levels of testosterone than women they tend to have more terminal hair. Testosterone also increases the size of hair follicles on men's faces at puberty so that they begin to grow visible beards.
While the rise of the metrosexual have seen growing numbers of men shave, wax and laser their way to less facial and chest hair, Gibbins says don't expect a hair-free man to evolve anytime soon.
"Evolution is much too slow for that sort of quick cultural stuff, " he says.
In fact, manscaping is more likely to subvert evolution than help it along.
"It's a classic example of cultural aspects completely overriding any evolutionary pressures, " says Gibbins.
So the next time you're bemoaning your hairy partner don't call them a Neanderthal, just pack them off to the beautician's instead.
Goosebumps: evidence of our hairy past?
Nearly every hair follicle on our body has a little smooth muscle, known as a piloerector muscle, connected to it. All these muscles have a nerve supply, so when the nerves are activated, the muscles contract and the hair follicles rise.
"Since most of our hair is so thin nothing much happens except the goosebumps. However, if we had more substantial fur in our follicles, like a cat or a guinea-pig, then this action would fluff up the hair, " says Gibbins.
Cats use piloerection to trap air in their fur when they're cold, and to make themselves look bigger when they're under threat.
Humans still have a complete set of neural pathways for both these responses which suggests we were using our piloerection system properly until sometime fairly recently in our evolutionary past, says Gibbins.
So when you next get a 'chill down your spine' just imagine how scary you'd look with all your hair standing on end!