This blog is for Florian and Stefania who are fabulous hosts.
A short time ago I was being a bon viveur in the back garden of friends - properly socially distanced of course. We were talking about evolution as one does, or I tend to do, with a glass of bubbly in one’s hand on a Covid-19 era afternoon amongst pleasant company - what else is there to do!
The issue of the lack of hair on most parts of a human body came up - what was the evolutionary advantage that created this feature which is almost unique to humans amongst primates and certainly quite different from our cousins, the great apes who are definitely hirsute. At one time along with most mammals we would have been covered in fur so what was it that made us shed our hair to become a naked ape?
My friend was convinced he knew the answer: bare skin would help humans keep cool through sweating when hunting in the heat of the day. This theory argues that the homo sapiens species started out as hunter-gatherers and we acquired the evolutionary advantage of shedding our hair and being able to sweat more easily, keeping us cooler, as we pursued our prey across the African savanna. It is true humans have more sweat glands than other apes - about 10 times more than chimpanzees.
The story is that we humans were relentless hunters who not only had the ability to run but also could outlast our prey by staying cooler as we pursued our next meat meal across the grasslands. The hunted animals, as they fled the remorseless homo sapiens, locked in their furry bodies, would eventually succumb to heat exhaustion while we, thanks to our nakedness, through sweating, could be there for the kill.
As homo sapiens spread out from Africa into the colder climes of Europe and beyond our hairless bodies then required the use of animal furs and the manufacture of clothes to survive the lower temperatures. The ability to don coverings, clothes and light fires led to our species being able to inhabit most of the planet and presaged the Anthropocene Age - the period during when human activity has been so dominant across the planet as to influence the climate and the environment.
This hypothesis about bare skin helping us to sweat to keep cool makes sense but there are other theories about how we came to lose our hair. One suggestion is that we were once semi-aquatic, inhabiting the seashore, living off shellfish and other marine creatures. To make ourselves smooth and therefore more successful in water we lost our hair. It is certainly true the less hair you have the faster you can swim - modern competitive swimmers often shave their bodies to gain those extra seconds through the pool. However, although it is an attractive hypothesis, there is little evidence to support this theory.
Another idea is that our ancestors became naked as a means to reduce the prevalence of external parasites that routinely infest fur. A hairy coat can host biting insect life, like ticks, lice, and other parasites. Such nasty creatures can carry viruses and bacteria such as malaria, sleeping sickness, Lyme disease and other dangerous illnesses. Humans, through the discovery of fire, eating of high calorie cooked meat and their ability to make clothes could have shed their hair, had healthier lives by reducing the number of parasites and still stayed warm at night.
A further theory is linked to our unique social relations (see my blog on our big brains: https://timboatswain.wixsite.com/website/post/big-brains-and-social-groups ). The idea is that we lost most of our hair in order to socialise in a way other great apes cannot: not only could we recognise people more easily but we could also read other individuals' emotions, through their facial expressions or autonomic reactions like blushing. Nakedness, and soft smooth skin, therefore, helped social relationships, sex and thus stimulated successful reproduction: it was, and still is, a crucial element in sexual attraction, visual beauty, leading to pair bonding, human ‘early’ birthing and so ultimately the evolution of our bigger brains.
It has been suggested that as human societies cooperated more it was vital that they could communicate effectively. They needed to warn, assist, instruct others and woo the opposite sex. By miming and using facial expressions they could indicate information to each other. The idea has also been mooted that as communication became more sophisticated the noises that accompanied the facial expressions and body movements could have been the beginnings of language - and it is certainly true that most cultures like to talk with their hands, faces and body language, as well as their mouths.
As yet, however, none of these theories can be proven, so you take your choice. There are issues with all the theories about humans' evolutionary hairlessness, though the front runner is still the idea we lost hair to stay cooler. Perhaps one day the geneticist will come up with an answer but at the moment we still do not understand how our sweat glands are made.
As a footnote, I have also been asked by puzzled interrogators why, though we are mainly naked, we have retained some hair on our heads, our armpits and the pubic regions. As so often the answer again is probably sex: it is believed it is because the hair in these parts is a sexual signal. Head hair for women is a sexual attraction and women’s hair has been and is often culturally curbed to control female sexuality. Hair in the pubic region and under the arms is believed to carry pheromones, odours that unconsciously send out sexual signals of attraction. If this is true it is a paradox that the human population likes to spend a fortune on deodorants!
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