Re: Hominid Altitudinal-Latitudinal Adaptations
John Waters (jdwaters@dircon.co.uk)
24 Oct 1996 19:27:15 GMT
Anton Uriarte wrote in article
<54e2h7$ouv@clark.zippo.com>...
> In article <01bbbe9f$a94a0aa0$5c2770c2@default>
>
> I see a difficulty in the theory.
> I think there is a fifth climatic adaption, and very
important indeed.
> Moving north the uvb radiation
> is much reduced, and the uvb radiation is essential
> for the synthesis of vitamin D and the fixation
> of calcium in the bones. So moving in latitude from the
ecuator
> the human skin need to become lighter to
> improve the absortion of the uvb radiation.
> But in altitude the effect is the contrary : uvb
radiation
> increases, so there is better for the human being to have
a darker skin...
>
> Anton Uriarte
> Department of Geography, Prehistory and Arqueology
> University of the Basque Country.
>
JW: Thank you Anton. I am not sure I fully understand the
point you
are trying to make here. However, the uvb radiation factor
is
important.
As far as altitudinal adaptation is concerned, it would
only be
important above the tree line. Below this point, the
equatorial
mountains have plenty of tree cover. At their base are the
usual
rain forest hardwoods. In the subtropical and warm
temperate
altitudes you find the usual mediterranean evergreens and
deciduous trees. In the cool temperate altitudes there are
the
familiar Silver Birch trees, which you probably have in the
Pyrenees. All of this tree cover provides plenty of shade
for
ground dwelling mammals.
However, in the higher latitudes the equatorial forest
gives way
to savannah and desert environments, where uvb exposure is
greatly increased. This would make the
altitudinal-latitudinal
adaptation route even more essential for mammals.
If we include the uvb factor, the mammals which adapted to
higher altitudes would need a minimum of two simultanous
adaptations as previously stated. However, mammals wishing
to
adapt directly to a higher latitude would require a minimum
of
five simultanous adaptations.
Is this the point you were trying to make, Anton? If so,
it is a
very good one. The uvb factor raises certain doubts about
the
Red Sea Theory of Human Evolution. It will be interesting
to
hear Paul Crowleys reaction to your reply.
John.
The ridddle of life: What regular sided solid can be
divided into two equal halves in such a way that each half
is exactly the same shape and exactly the same size as the
original solid?
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