Re: Bi-paedalism and Hair loss connected.
John Waters (jdwaters@dircon.co.uk)
20 Sep 1996 03:50:47 GMT
Mark Shuttleworth <insight@iafrica.com> wrote in article
<01bba609$e1648b80$8f121fc4@mark-win95>...
>
> Bi-paedalism
>
> Previously Un-published letter to SA Journal of Science Dated
8 June 1990
>
>
> I found the article by Mrs R Eickhoff, on the origin of
Bi-paedalism in
> your Volume 84 June 1988, most interesting.
>
> G V G Shuttleworth
>
JW: Thank you for the prescient article, Mark. It was most
welcome. Although Mrs Eickhoff's letter appeared to show traces
of cultural bias, I think she was working on the right lines.
Mammals are homoiothermic. This means that they can maintain a
constant body
temperature irrespective of environmental changes. They create
heat through their metabolic processes and lose heat (mainly)
through their skin.
Mammals such as Whales, who live in an environment with a
constant temperature
differential tend to have a similarly constant type of
insulating material, such as
subcutaneous fat or blubber. By contrast, mammals who live in an
environment where there is a fluctuating temperature
differential tend to have body hair or fur. The latter form of
insulation can be varied according to demand. Seasonal
variations can be achieved by the process of moulting in the
summer, or growing a new coat of fur in the winter.
Apes tend to live in equatorial regions where there is
relatively little seasonal change, but where there can still be
considerable diurnal/nocturnal changes in temperature. As a
result, Apes have fur or body hair, but do not normally moult or
grow winter coats.
I think it is reasonable to assume that our Ape ancestors had
similar body hair characteristics to present day Apes.
Furthermore, I think it reasonable to assume that present day
Hss characteristics in respect of body hair etc., are an
adaptation to a change in thermoregulation requirements.
But how and why? An examination of certain post natal
characteristics of Hss babies may reveal some answers here.
Furthermore, a consideration of the subcutaneous fat in the Hss
female may prove fruitful.
Human babies are sometimes born with a good head of hair, which
they subsequently lose within a week of birth. This condition is
known as the moulting of the fetal hair. It has no apparent
purpose. But things which have no apparent purpose today may
have had a very important purpose at an earlier stage of hominid
evolution.
Consider the differences in the way in which Chimpanzee babies
and Hss babies are carried by their mothers within the first few
weeks after birth. The Chimpanzee baby is carried underneath its
mother. The Hss baby is carried in its mothers arms. So what?
The Chimpanzee baby produces body heat through its metabolic
processes. It dissipates the heat mainly through its skin. The
baby is not as hairy as an adult, but it is still much hairier
than an Hss baby. Why?
If our Ape ancestors tried to carry a relatively hairy baby in
their arms (in the manner of a present day Hss mother), the skin
of the Ape baby would press against the mothers chest and arms.
This would reduce the amount of skin exposed to the air. As a
result, less heat would be dissipated from the baby's body. So
the baby's body temperature would rise. If the baby was carried
in its mother's arms for any distance, the baby's core
temperature could rise so much that the baby could die of
heat-stroke.
The thermoregulation problems of such a baby could be resolved
through the moulting of the hair on its head. A Hss baby
dissipates thirty percent of its body heat through its head.
By extension, the present day Hss characteristic of the moulting
of the fetal hair, implies a correlation between the bipedal
carriage of ancestor babies and the thermoregulation adaptations
perceived in present day Human beings.
And another thing. There is very little difference in the
subcutaneous fat level or male and female Apes. However, in the
human specie the female has between 12-15 percent more
subcutaneous fat that the male. Why is this?
The subcutaneous fat of Hss females is not evenly distributed
over the whole of the body. It is concentrated in certain areas.
Perhaps not surprisingly in the context of this reply, the fat
is found to be positioned exactly where the Hss baby comes into
contact with its mother when it is being carried. When the baby
is very young, it is held close to the mother's chest. When it
gets older, it tends to be carried on the mother's hips. The
reason for the fat? To prevent the mother's own body heat from
being transmitted to the baby. So the baby gets a nice cool
ride.
By extension, this characteristic developed as a maternal
adaptation to the problems of an overheating baby. So why do we
adults have nine times as many sweat glands as the Apes? Because
we are all grown up babies. If we need improved thermoregulation
devices to survive as infants, we cannot discard such
characteristics when we grow up.
John Waters
John Waters is the author of "Helpless as a Baby",
a book concerned with general and human
evolution. It may be accessed at URL
http://www.dircon.co.uk/jdwaters/HAAB.htm
jdwaters@dircon.co.uk
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