We will take a look at humans in the following article. It is a good place to start if you are new to the subject. There is a lot more information available for those that want to make a more detailed study.
A Hairy Issue For Humans
Author: John Prytz
The amount of your hair from the neck up is different from your hair (what little there is of it) from the neck down. There are sexual differences with respect to hair between the human male and female as well both from the neck up and from the neck down. The curious part is that neither neck up or neck down or sexual differences tend to have close parallels with nearly all the rest of the terrestrial mammalian kingdom, mammals we presumably naturally evolved from. The 64 cent question is why?
Humans vs. Mammals: Humans tend to have way less body covering usually termed hair and/or fur relative to other mammals, our size or below, including our primate ancestors. That our first uniqueness. Why is that? Now apparently our lack of fur, why we lost the fur we presumably once had way back once upon a very remote time ago, was because we developed sweat glands to regulate heat, which, IMHO was a retrograde development.
Fur is a good regulator whether retaining or allowing body heat to escape. Some animals, like cats, shed some fur as the warmer weather approaches, though it thickens again as winter approaches. Sweat glands are only a cooling mechanism. That’s okay. But be that as it may, the ‘why’ question now becomes one of explaining why humans alone out of all our primate cousins developed sweat glands thus contributing to the evolutionary loss of our fur. You’d think what’s good for the human is also good for the gorilla, chimpanzee, gibbon, orang-utan, etc. So, why were humans and humans alone selected to be ‘the naked ape’? Was it a normal natural selection, an evolutionary fluke or by design?
Neck Up / Neck Down – Distribution: For the human species, there’s an obvious dichotomy between the amounts of hair we have from the neck up relative to the neck down. But any breed of cat, or dog say will tend to be just as furry neck up as neck down. Why do we have a neck up / neck down division to our relative hairiness? Was it normal natural selection, an evolutionary fluke or by design?
Neck Up / Neck Down – Haircuts: From the neck up, humans tend to need to have the occasional trim or haircut, or shave. But, humans, like the rest of the mammals, don’t need haircuts from the neck down. To b honest, the rest of the mammals don’t need haircuts from the neck up either, unlike humans. Why is that? Why do humans need haircuts? Was it normal natural selection, an evolutionary fluke or by design?
Sexual Differentiation: Hairiness or furriness has no obvious sexual differentiation in nearly all the rest of the mammals; male cats of any particular breed will have as much hair on their bodies as their female counterparts, although male lions have manes that lionesses don’t have. Still, lions and lionesses apart, that sexual distinction is part and parcel of the human species. In humans, males tend to be way more the hairier in terms of overall body covering. Males also tend to have far more hair on the front of the face – beards and moustaches. But that’s not always true on top. When it comes to hairiness, there’s not only a neck up / neck down division but a differential between the sexes. Why is that so? Was it normal natural selection, an evolutionary fluke or by design?
Natural Pattern Baldness: I need start here by making a distinction between thinning hair which a goodly percentage of human males and females experience as they age, and baldness. Some human males, percentages increasing with ever increasing age, tend to lose, for reasons apart from disease, stress, chemotherapy, etc., more of their hair up top – the common occurrence called male pattern baldness or partial baldness or massive thinning of the hair on top. But whether to a greater or lesser degree, there’s not an inevitability of hair thinning and total loss of hair up top with age in human males. That alone suggests that aging isn’t the be-all-and-end-all of the condition.
Human females, though to a far lesser extent, will also tend to exhibit hair thinning (as opposed to total baldness), again, percentages going up as one’s age goes up and up. On balance however, you see far, far fewer females than males with bald spots relative to gradual hair thinning.
It’s an unfortunate fact of life that I’ve got a lot less hair up top today than I had in my teens. That applied to my father and equally as well to my father’s father. The question is why is baldness an unfortunate fact of life for some since baldness isn’t a fact of life for all human males; it certainly isn’t as much of an issue for the female of the species (another of those sexual differentiations noted above). Baldness certainly isn’t a fact of life for most hairy or furry species (another human vs. animal data point to be added to the above), like our companion animals, be they cats or dogs, mice or rats, rabbits or guinea pigs, ferrets or alpacas. However, the thinning of the hair isn’t quite uniquely confined to humans. Some primates, but only a relatively few species, show some progressive thinning of their scalp hair following their version of puberty.
So baldness tends to be fairly obviously a sex-linked genetically transmitted condition that arose as the result of some genetic mutation in an ancestral primate and/or human male multi-thousands upon thousands of years ago, way before the start of written history. But lots of questions arise. Why balding on just the top of the head; why not, especially with inevitable aging, the entire head (and face)? Why not the entire body’s covering of hair? Humans have so little fur that the thinning and loss of the rest of it shouldn’t matter really. [There are medical conditions that do involve total facial, even in extreme cases total body hair loss, but they aren't related to normal hair thinning and baldness.]
If hair thinning and eventually baldness (in some individuals) confers no evolutionary advantage or disadvantage why is there nothing similar in any other non-primate mammalian species? Actually there might be an evolutionary advantage in that genetically linked hair thinning and eventual baldness presumably started with one mutation in a statistical sample of just one individual (perhaps even one of our ancestral primate cousins) which has now spread to include a reasonable minority of adult males (or majority of adult males, even females if you count just hair thinning and those over 60 or so). However, why did that original mutation spread as it obviously did? What could that evolutionary advantage actually be? And if there is an evolutionary advantage, why isn’t the condition more widespread throughout mammalian species? For the moment, those questions stump me. Was it normal natural selection, an evolutionary fluke or by design?
Spots / Stripes / Plain: Humans, from the neck up, have a single natural hair colour. Human hair tends to be blonde, red, brown or black (I’ll ignore grey/white since that’s an aging issue). So here we have one species, four different hair colourations. Mammals of any one species tend to be one of two colour patterns, neither of which has a parallel akin to the human condition. Either all members of a species are just one plain colour and only that colour; polar bears are white; brown bears are brown (the very rare condition of acquiring the genetic mutation and ending up an albino is a separate issue), or else all members are multi-coloured with spots, stripes; often an irregular pattern. All humans, one species, aren’t all the same with respect to hair colour like brown bears – some humans are blonde, or black or red-haired. Tigers have stripes; leopards have spots; calico cats tend to be multi-coloured with an irregular symmetry. Humans have neither stripes, spots nor an irregular colouration pattern. Why are humans different from other mammals when it comes to the general rule of one species – one hair colour, or one species – multi-coloured fur patterns? Was it normal natural selection, an evolutionary fluke or by design?
But the biggest anomaly of all is what natural environmental changes – triggers – survival-of-the-fittest scenarios transpired that could account for all these differences between the human mammal and the rest of the mammals blessed with fur? It’s not an advantage one would think to need a haircut; the amount of relative hairiness between males and females, including baldness, is great enough to require an explanation, but I can’t think of one; and there would appear to be no advantage in humans coming in four basic hair colours, yet no combinations of those. It is all very strange.
Summary: Non-human mammals our size or less are way more covered in hair or fur than humans. Non-human mammals show no sexual differentiation in their hairiness or furriness. Nearly all non-human mammals show no neck up/neck down differentiation with respect to hair covering. Non-human mammals don’t need haircuts. Non-human mammals don’t go bald though some primates exhibit hair thinning. So what’s up with humans? Were all these anomalies just normal natural selection, an evolutionary fluke or by design? And if by design; whose design? It’s a hairy issue!
Article Source: http://www.articlesbase.com/nature-articles/a-hairy-issue-for-humans-5145169.html
About the Author
Science librarian; retired.
Obviously, there is a lot more to know about humans. This brief article is just a start, and the next step is to do some more research. In any case, the tips in the article set the stage for a more detailed treatment of the subject.