Evolution of Human Hair
Occidental
1. In humans, male and female, uncut it will grow to a length of 2 to
3 feet
2. Long head hair has no obvious practical use (?sexual signaling of
some kind)
3. Most of the inhabitants of sub-Saharan Africa have wooly hair,
whereas all the diaspora populations have hair of some other kind
(straight, curly - Australian aborigines, though black, have "shaggy"
hair)
4. No other mammal has hair like sub-Saharan Africans
5. The human scalp is richly endowed with blood vessels - lacerations
to the scalp bleed profusely, in hot weather one can cool down rapidly
by directing cold water onto the scalp.
6. Many men and some women go bald, often in early life (which
disposes of the sexual signaling theory)
Can we construct an evolutionary tale to explain these facts,
particularly number 6, and can we elevate it from a mere story to a
hypothesis by designing an experiment to test it? Yes, I believe we
can:
The enrichment of the scalp with blood vessels is obviously a cooling
mechanism
Straight hair lies flat on the scalp and does not permit cooling
Wooly hair creates interstices near the scalp, permitting air flow,
while simultaneously acting as a sun-shade by bunching up into a dense
cap over the head
The above arrangement evolved for pre-sapiens African hominids
The diaspora populations had no need of shade from the sun, so their
hair reverted to a more typical mammalian type, but retained the
longer-than-chimp hair length of their African ancestors
Baldness developed, but was not maladaptive for obvious reasons
and here we are today
How would we test it? By demonstrating that wooly hair has the
advantages I list above.
moschops
> 6. Many men and some women go bald, often in early life (which
> disposes of the sexual signaling theory)
>
> Can we construct an evolutionary tale to explain these facts,
> particularly number 6, and can we elevate it from a mere story to a
> hypothesis by designing an experiment to test it?
But usually not before they've spent enough years mature enough to
reproduce.
r norman
You make many assumptions, only some of which may be true.
The argument that long human head hair developed as a thermoregulatory
device is not well supported and has many critics. There is no reason
to suspect that tightly curled hair of sub-Saharans is
thermoregulatory. Facial hair, axillary (arm pit) and pubic hair, and
male pattern facial, chest and back hair clearly have sexual signaling
roles. There is no reason to suspect that head hair not to share
either that sexual or an important social signalling function.
Probably the worst in number 6 where you claim that male pattern
baldness clearly proves that hair is not a sexual signal. In fact,
most people would argue that male pattern baldness demonstrates just
the reverse being a product of testosterone concentration.
Alternatively you could argue that late developing baldness, after the
peak reproductive period, removes it from consideration as a sexual
signal. That would still leave it suitable for a social signal, much
the same as grey hair.
You should also take a look at some pictures of unusual hair styles in
animals to see that human hair is not that much of a departure.
B. Thierry argues for a cultural role of human head hair in "Hair
Grows to be Cut" (Evolutionary Anthropology: 14(1) p. 5), saying
"hominin development of clothing and the use of fire made fur no
longer useful. Following this rationale, body hair became redundant
with the development of cultural artifacts. Our naked appearance would
hence be a biological outcome of the advent of cultural evolution.
Coming back to the unusual length of our head hair, we cannot help but
see a strong contrast with the reduced hair on most parts of our
bodies. I propose the same general origin for both physical
characters: the advent of culture....hair features are signs that
herald the cultural identity of their bearer, providing cues about
tribal belonging, rank in the community, marital status, and value or
history of individuals. Continuous growth is the critical character
giving humans control of their hair. It provides an abundant and
renewed matter allowing for the shaping of hair style and obtaining
elaborated forms. The same may be said for beards and whiskers, with
the additional occurrence of sexual selection." (S)he adds that
blushing, tears, and the whites of the eyes are also significant
social signs of a similar nature, concluding "Such hypotheses are, of
course, difficult to test. For head hair, it is suggested that the
genetic changes that cause continuous growing occurred some hundred
thousands years ago.1 If that holds true, it would correspond to the
period preceding the emergence of Homo sapiens."
A. Jolly has the same conclusion in 'Hair Signals" (same page of the
journal) saying "I suspect that the genes that make human head hair
keep on growing and tangling are positively selected as honest
signals, just as much as are the self-maintaining hairdos of primates
like cotton-top tamarins or toque macaques.... Judith Berman points
out that we denigrate our ancestors by drawing them with wild hair,
but figurines of 25,000 years ago show women naked with beautiful
braids. Coiffure and coiffure-demanding genes could be at least as old
as Homo sapiens"
Terence Kealey argues the same point in "Glad to be naked"
http://www.newscientist.com/channel/life/evolution/mg16321985.400
"what if the evolution of our head hair only really got going after we
had acquired the intelligence to make cutting tools? Hair that grows
quickly provides a wonderful raw material for the minx or Don Juan who
want to cut it into ever more novel shapes. "
There is ample evidence that selection can produce continuously
growing hair. Domesticated sheep and some goats have significantly
altered hair growth patterns from artificial selection; it is quite
possible, even quite likely, that strong sexual selection for hair
growth could produce significant changes in the pattern inherited from
furrier ancestors. Also hair growth is strongly dependent on
nutritional status and level of physical activity. Modern sedentary
and well fed life styles promote rather longer hair so that it is not
necessarily true that our ancestors had quite such long head hair.
Many animals have unusual patterns of hair growth usually indicative
of sexual selection (the lion's mane, for example) or other adaptive
functions (a horse's tail, for example). Hair patterns seem rather
flexible in evolutionary terms and should readily be strongly
influenced by sexual selection. See, for example,
Hair, Human Evolution, and the Idea of Human Uniqueness
Niccolo Caldararo
Evolutionary Anthropology Volume 14, Issue 4 , Pages 132 - 133, 2005
Lucifer
> First, some interesting facts about hair
> 1. In humans, male and female, uncut it will grow to a length of 2 to
> 3 feet
Mines longer than that :p
> 2. Long head hair has no obvious practical use (?sexual signaling of
> some kind)
I use it as a blanket :p
J.J. O'Shea
(in article <1193594366.7...@19g2000hsx.googlegroups.com>):
> 4. No other mammal has hair like sub-Saharan Africans
One wonders from whence came the name 'buffalo soldiers', one does.
<exit, stage left, to the music of RN Marley>
--
email to oshea dot j dot j at gmail dot com.
Kermit
> First, some interesting facts about hair
> 1. In humans, male and female, uncut it will grow to a length of 2 to
> 3 feet
> 2. Long head hair has no obvious practical use (?sexual signaling of
> some kind)
> 3. Most of the inhabitants of sub-Saharan Africa have wooly hair,
> whereas all the diaspora populations have hair of some other kind
> (straight, curly - Australian aborigines, though black, have "shaggy"
> hair)
> 4. No other mammal has hair like sub-Saharan Africans
Baaaah. Humbug.
> 5. The human scalp is richly endowed with blood vessels - lacerations
> to the scalp bleed profusely, in hot weather one can cool down rapidly
> by directing cold water onto the scalp.
> 6. Many men and some women go bald, often in early life (which
> disposes of the sexual signaling theory)
>
> Can we construct an evolutionary tale to explain these facts,
> particularly number 6, and can we elevate it from a mere story to a
> hypothesis by designing an experiment to test it? Yes, I believe we
> can:
>
> The enrichment of the scalp with blood vessels is obviously a cooling
> mechanism
> Straight hair lies flat on the scalp and does not permit cooling
Hence we older male athletes are equipped with a direct scalp-cooling
air interface.
> Wooly hair creates interstices near the scalp, permitting air flow,
> while simultaneously acting as a sun-shade by bunching up into a dense
> cap over the head
> The above arrangement evolved for pre-sapiens African hominids
> The diaspora populations had no need of shade from the sun, so their
> hair reverted to a more typical mammalian type, but retained the
> longer-than-chimp hair length of their African ancestors
If our head hair was as curly as possible in Africa, then mutation
would have nowhere to go but straight. I don't see it as reverting at
all
> Baldness developed, but was not maladaptive for obvious reasons
>
> and here we are today
>
> How would we test it? By demonstrating that wooly hair has the
> advantages I list above.
My wife and I have speculated that wooly hair has advantages in the
sub-Saharan environment, but not necessarily elsewhere. We are the
running ape, after all. It may have provided shade and sex appeal
while we dropped the rest of the fur as part of our superior cooling
system.
At the time of the diaspora, technology had advanced enough that we
may have had combs, or braids, or cutting with blades, and straight
hair mutations were not the disadvantage they would have been 100,000
years ago or in southern Africa.
Kermit