Ah, autumn in Claremont. That distinguished time of year when
the weather fluctuates from “how can 60 degrees be so cold” to “this sweater
really gets the pit sweat going” in the span of a single, 50-minute lecture.
The trees seem to vaguely realize winter might saunter on through, and one
or two might get around to changing color by December. Yes, it’s the time of rain
(we’re supposed to get rain, right?) and crisp afternoon air; rapidly changing
pie preferences and holiday-themed 5C parties; and thesis stress and hipster
fashion heaven.
It’s got
me thinking about body hair. Humans are Earth’s only hairless primate, so
when the weather cools down like this I’m invariably led to wonder: Where did
all our hair go? How nice would it be to have an ever-present, sweat-wicking
base layer of hair on your whole body? No more fickle fashion decisions 10
minutes before class. No more forcing yourself to put on pants just to hit Snack. All you’d ever need is a light jacket, some skivvies and a nice brush!
You might be
thinking something along the lines of: “Sure, sounds pretty dope, in theory, but
clearly you’ve never lived here over the summer. A full-time wolf costume would
be WAY too hot.” You’re right—I’ve never been in Claremont
for the summer. But more importantly, your claim that a coat of fur would be
too hot in warm, dry weather was actually the first theory as to why humans
were evolutionarily stripped of their body hair.
Beginning in the 1960s, scientists
and anthropologists posited that Homo
sapiens, who evolved as two-legged primates that nomadically hunted
throughout East African savannas, lost their hair to keep them cooler on the
arid grassland. As the theory went, early humans with less body hair died less
often from overheating (‘hyperthermia’), so they were more likely to reproduce
on average and propagate genes for reducing body hair.
While this hypothesis makes much
intuitive sense, it does not hold up upon inspection. The biggest flaw in the ‘cooling device’ theory is that body hair actually acts as an insulator to regulate body temperature. During the day, fur protects skin from the sun so
the body absorbs less heat, and, at night, having a full pelt keeps the skin
warm and prevents heat loss through conduction.
There are a bunch of other ideas as
to why humans could have lost their hair, which tends to happen when people
speculate about something that occurred 1.2 million years ago (that number
according to 2004 genetic analyses by Rogers and colleagues). Maybe we lost our
fur as a way to become agile hunters in the ocean, as in the ‘aquatic ape’ hypothesis? Could be, except this theory falls victim to the same issue as the
cooling-device hypothesis: Hairless primates would lose body heat extremely quickly
in the water.
How about the ‘carrion-eating’ hypothesis, which holds that messy eaters in the animal kingdom (vultures and
condors, e.g.) are bald on their head and neck because it provides them some
advantage when eating rotted or messy meat? Perhaps humans found evolutionary
fitness in this same mechanism? Perhaps, though it doesn’t explain why men have
retained androgenic hair about the mouth.
There are at least four other models
for humanity’s hair loss, but the most compelling hypothesis comes from Markus Rantala, a Finnish scientist so smart he has a doctoral degree in both biology
and psychology.
Rantala published a paper in 1999 elaborating
on an idea put forth by Thomas Belt all the way back in 1874, in which Belt theorized
that bare skin was advantageous because it prevented infestation by ectoparasites
such as ticks, known for carrying disease. Belt’s theory was largely forgotten
because a guy by the name of Darwin (a.k.a. ‘ol Charlie D.) rejected it,
claiming that parasites threatened all other apes, so it wouldn’t make sense
for humans to be the only naked primate.
And Darwin was right—it doesn’t make
sense—unless you consider the evidence put forth by Rantala, who argues that early
hominids differed from other primates in that they established ‘home bases,’ or
shared dens, that housed a collection of hunters and their mates. In short, we
went from nomads to cavemen. This shift to living in communal shelters provided
ectoparasites a unique opportunity: infest a large den of unwitting host hominids
all at once.
Indeed, humans are the only primate of 193 species able to be
infested by fleas, an ectoparasite that requires host animals to live in a
permanent den. We must look like pretty gross naked mole rats to those other
192 species. Furthermore, the shift to communal living is estimated to have
occurred around 1.8 million years ago, temporally in line with the approximation
that our nakedness came about 1.2 million years ago. Consider, too, that one of the
best medical treatments for ectoparasitic infestation is to simply cut off the
pest-ridden hair.
Rantala goes on to surmise that the
increased reproductive fitness associated with less hair (thus fewer parasites)
led men to sexually select for hairless women as women were more likely to
spend time in the group den and were therefore more likely to be infested. This
method of sexual selection, according to Rantala, consequently increased the
speed of our descent into immodesty.
Personally, I take this aspect of his explanation
to be too perilously aligned with Westerners’ current cultural values. I find
it highly unlikely our sexual preferences are driven by the desires of ancestral
humans 1.2 million years ago, and instead I turn to more modern arbiters of
cultural preference, like, oh I don’t know, the Internet.
Whatever the reason for humanity’s
bare skin, I still think it’d be way cooler if we all had fur. Full-body
cornrows, anyone? Dye your whole body with cheetah print? Alas, I can only
wonder, and speculate ruefully, on a bushy world that could have been.
Warren Szewczyk PO ’15 is a neuroscience major who also co-hosts the radio program Reality Check, which explores the intersection of science and the spirit. In his spare time, he is an avid writer of spoken-word poetry.
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