The Selective Advantages of Hairlessness, Baldness, and Gray Hair

 
Denyse O'Leary collects silly Darwinian tales of the sort usually referred to as "just-so" stories. She alerted me to some real live ones on her blog Uncommon Descent [Darwinian fairy tales: Why middle-aged men have shiny scalps].

It's embarrassing that the creationists have such easy targets.

The just-so stories are written by Terence Kealey who bills himself as vice-chancellor of Buckingham University. (He's also a clinical biochemist.) The stories were published on Times Online as: Guys, be glad to be grey or thinning on top.

Here's are the funny parts ....

We human beings, too, are highly selected sexually, but in our case it is women who are the peacocks: the more beautiful they are, the greater the number and quality of the men who court them. This is why, some 75,000 years ago, we made our last two evolutionary advances: we lost our body hair and we invented art.

...

Art and hairlessness co-evolved because they fed off each other. The girl whose skin was least hairy could paint it, tattoo it, decorate it and clothe it more adventurously than could her furry sisters. So she got more and better men. And in consequence her children - even the males, though to a lesser degree - lost their hair too. We had become the naked ape.

This was all supposed to happen about 75,000 years ago, according to Terence Kealey. It's interesting to speculate on what must have happened.

Small groups of hunter-gatherers met from time to time. Almost all the females probably had sexual partners when they were all hairy. It's unlikely that there were many females who couldn't find a mate.

All of a sudden, there were some new girls on the block. They had less hair and they covered their body with paint and tattoos. These mutants were so attractive to men that they were preferentially chosen as mates and, more importantly, their hairy sisters were ignored. The hairy women didn't have offspring so there must have been quite a few men who were celibate as well. (Unless the mutants had multiple mates.)

That's why hairlessness was rapidly selected.¹

In order to understand the next just-so story you have to know that the article begins with an explanation of why Silvio Berlusconi, the Prime Minister of Italy, had a hair transplant.

Which brings us back to Mr Berlusconi. Hair plays a social signalling role in many older mammals. It goes grey - which can be a good thing. It is only the silverback gorilla(so-called named for obvious reasons) who can corral a harem of females, in part because gorillas of both sexes revere older males. We have retained our head hair so enabling that social signalling: grey hair on men can reinforce an alpha message of chiefdom. As can baldness.

Men have evolved to attract women. Because only some men go bald, we must assume that different women are attracted differently. Some women will be attracted to young men, but young men are untried and therefore risky, so some women will seek sugar daddies instead. Mating with sugar daddies invokes a different set of risks but the trophy wife is nonetheless making a rational choice - one that may well have been rewarded preferentially in the Stone Age - to which she is in part guided by baldness in her man.

Now, what sort of girl will fancy Mr Berlusconi? Clearly the sugar daddy type. But such a girl will subconsciously be looking for baldness in her beau and she may be put off by the mixed messages Silvio's head is transmitting.

The biology of baldness is complex. Some theorists believe that it renders older men so unattractive that - rather than sowing additional wild oats - they are forced to spend more time with their families and so help their children to survive. But the myriad Becky Sharps in literature and history help to disprove that theory.

Now let's imagine that we are back in the stone age. There are a bunch of men who, for undisclosed reasons, have reached the age of fifty and don't have a mate.² There are a number of young women who want an older man for a mate instead of the young men who are probably available.

Most of the fifty year olds have hair that's the same color it has always been. All of a sudden a few mutants appear who have white hair or (gasp!) no hair at all. These older men become so sexually attractive to the young women that they get to reproduce while their hairy friends are spurned. Maybe they painted or tattooed their bald heads. Yes, that would work. I think I'll try it.

That's how the alleles for baldness and white hair get selected in ancient hunter-gatherer societies.

---

1. It's a good thing that razors hadn't been invented, otherwise the hairy women could have fooled the men into thinking they were a hairless mutant.

2. I'm assuming monogamy as the default option. As far as I know, this is generally accepted.