No, the tropical sun theory isn't the end of the story. The same textbook
goes into the difference in bone structure, etc. as well. It brings up two
rules, called "Bergmann's rule" (relation of body mass or volume to surface
area) and "Allen's rule" (shape of body, especially appendages). I don't
have time today to type the whole thing, but the gist is this:
1) Body size tends to be greater in populations that live in colder
climated, because, as mass increases, the amount of relative surface area
decreases. Heat is lost as the surface, so increased mass allows for
greater heat retention and reduced heat loss.
2) Similarly, relatively shorter appendages, with increased mass-to-surface
rations, are apadaptive because they are more effective at preventing heat
loss. So, one would expect shorter appendages in colder climes, and longer
ones in tropical climes.
The conclusion offered by the book is that, "according to these rules, the
most suitable body shape in hot climates is linear with long arms and legs,
whereas in a cold climate, a more suitable body type is stocky with shorter
limbs. Considerable data gathered from several human populations generally
conform to these principles. . . .But there is much variability in human
body proportions, and not all populations conform so obviously to
Bergmann's and Allen's rules."
As for your other question, I don't think anyone believes that human races
diverged before we were furry animals, or even before we were Homo sapiens
sapiens. (Bear in mind that I am a philosophy major who has only taken a
couple of first-year courses on these matters, however, so my opinion can
hardly be considered authoritative.) The picture I saw presented in these
classes, anyhow, was of modern humans originating in Africa and then
spreading across the world from there. How exactly populations spread is
probably not altogether clear in many cases, but I think many of the
apparent counterexamples to Bergmann's and Allen's rules could possibly be
explained by understanding exactly when a given "race" arrived in its
current environment, and how. (For example, I personally have no clue why
the Ainu, the native inhabitants of Japan, have essentially caucasian
rather than asian features. But if we knew exactly how and when the Ainu
arrived in Japan [and maybe anthropologists do, for all I know], we might
be able to find out.)
This much I will say, however: "race" is probably not really a useful term
in any physical science. Race is a primarily (or even entirely) *cultural*
term: we tend to index people based on where they live and how they
(culturally) behave, and how their appearances might differ from our own.
But appearances, of course, are superficial, and wouldn't correspond to any
really significant or consistent *genetic* differences. Just as Gray
Squirrels come in different colours (some are grey, some tan-coloured, some
black) humans come in different colours; but both grey, tan, and black Gray
Squirrels are still of the same species, and so too are all humans of the
same species. (Remember, much racism is predicated on the false belief
that difference in race corresponds to some difference in species.) We are
all Homo sapiens sapiens, and that alone is conclusive refutation of racist
theories.
(Incidentally, I would love it if anyone with some significant background
in these matters would comment. I'm way out of my own field of study, so I
can only hope my points are essentially correct. Hey, doesn't anyone want
to talk about the mind/body problem or Plantinga's reformed foundationalism
for a while? ;)
Regards,
Mike Hardie
<hardie@globalserve.net>
http://www.globalserve.net/~hardie/dv/