Re: puzzle of the negrito: isolated archaic populations
Dan Barnes (dbarnes@liv.ac.uk)
Mon, 16 Dec 1996 14:46:31 GMT
In article <58sf76$dtl@news.sdd.hp.com>, geroldf@sdd.hp.com says...
>I'm wondering about your second point: why would you expect sexual
>selection to play a role?
It was just a side point really but it is known to have affected melanin levels in
Tazmania and the Andes.
>He
>|> examined the width of fossil Apiths and H.e. (admittedly a very small sample
>as
>|> pelvises, which he used, are rare) and showed that they fit into a general
>|> climatic distribution of moderns. Since, in the generalisation of the human b
>ody
>|> (a cylinder), there is no change in surface area to volume ratios with increa
>sing
>|> height he came to the conclusion that the difference in height correlated to
>the
>|> greater volume need for water storage that a savannah dwelling hominid
would
>|> need.
>
>Risky conclusion; human morphology ranges over a wide spectrum of
>area/volume ratios. It's one of the primary evolutionary responses to
>climatic conditions. The yahgan of tierra del fuego, who probably
>represented the most advanced physiological adaptation to cold among any
>modern humans, had very truncated extremities. Some of the nilo-sudanese
>peoples, such as the watutsi, represent the other extreme; they are
>extremely tall and slender, with proportionately longer arms and legs. I
>haven't seen any data of how the area/volume (A/V) ratio of the pygmies
>compares with their taller neighbors, but they may be similar. Pygmies
>are not nearly as gracile as the watutsi, but because they are so much
>smaller, their A/V ratio is boosted. (Note: if the human body type is
>approximated as a cylindar, A/V is inversely proportional to size.)
Ruff also deals with the issue of adaptation of distal limb proportions which
show a similar climatic adaptation. The full ref for the article is:
Ruff, C.B. (1994) Morphological adaptation to climate in modern and fossil
hominids. Yearbook of Physical Anthropology. 37. 65-107.
>|> From these results it is not suprising that a people who have spent a long
>|> time living exclusively in rain forests would develop a decrease in height.
>
>Right, though the relative importance of temperature regulation and
>mobility in tangled overgrowth is unclear to me; both seem to be
>significant.
But (esp. with the last point) difficult to test for - I would have thought.
>It
>|> would seem that if Ruff's analysis is valid that it is an example of parallel
>
>|> evolution - with two groups of people adapting to similar environmental
>|> conditions.
>
>Entirely possible. The question then would be, from which ancestral
>population did the negrito evolve?
>
I would assume they evolved from African ancestors.
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