ThesisPDF Available
Modern Human Hairlessness
This short paper is intended to elaborate upon the dermal interaction described in
my article below, in terms of Human evolution. In particular the debate about
modern Human hairlessness, and increased sweating capacity.
The evidence outlined in my article indicates that the hair cycle and structure of
the follicle, evolved to take advantage of pressure based spatial growth controls,
recognised as controling all normal tissue growth in-vivo.
The link this makes with sweating capacity described in my article, strongly
supports the heat stress Hypothesis of Human hairlessness as described by
According to this dermal interaction the changes in dermal fluid levels and
pressures linked to environmental temperature changes, also change hair growth
and sweating capacity. In cold conditions hair growth is increased and sweating
capacity reduced, and in hot conditions hair growth is reduced and sweating
capacity is increased.
The important thing here in terms of Human evolution, is that the means to create
modern Human hairlessness and increased sweating capacity already existed in
hairy mammals and primates, and this is heat stress related. Over the long term
these heat stress response characteristics would become selected for, and a
permanent dermal condition in Humans. The evolution of the fat layer in Humans
could also aid in making our hairlessness permanent.
I think it is logical that the dermal fat layer we have, evolved alongside our
hairlessness and not before. There would be no stimulus for this while we still
had fur. I agree with Wheeler that this fat layer acts as a core temperature
stabilizer, that still allows efficient dermal heat shedding when necessary. This fat
layer could also restrict dermal tissue fluid drainage into deeper tissues, so
encouraging the permanently higher dermal fluid pressures that maintain our
hairlessness and increased sweating capacity.
I suggest that this mechanism of changes in hair growth and sweating capacity,
originaly evolved for temperature control. But anything that effects dermal rigidity
and fluid pressures, will also change hair growth and sweating capacity in
modern Humans.
I think the differences in eyebrow tissue physiology, could tell a story about the
baseline dermal changes in Humans, as i refer to in my article.
I also agree that scalp hair was important as Sun protection in early bipedalism,
as Wheeler describes. But modern Human scalp hair can grow over two feet
long. Having long hair hanging over your eyes and ears is a real problem in
terms of survival, unless by the time our hair got to be this long, we had also
developed the sense to tie it back or cut it? I think there is a logical connection
here to increasing scalp hair length through this dermal interaction, and the
changes necessary for the evolution of our brain.
I also think this recent in-vivo study is important.
The hard data here clearly confirms this dermal relationship in modern Humans.
Significant changes in hair growth are linked to significant changes in sweating
capacity. It is the modern Human link to androgen action in this study, that results
in the testable link to gender related diseases I describe in my article.
I would welcome any comments.
Stephen Foote
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