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Multi-Regional vs. Replacement, was This might be an even
J. Moore (j#d#.moore@canrem.com)
Sat, 13 May 95 18:24:00 -0500
Lj> basic theories re: the emergence of "modern" humans. Theory 1 seems to
Lj> be that earlier varieties of hominids (Homo Erectus) radiated out of
Lj> Africa hundreds of thousands of years ago and sub-populations descended
Lj> from these "migrants" independently evolved into "modern" humans in a
Lj> bunch of different geological areas.
This is not quite what the multi-regional hypothesis says; although my
reply here might seem like a silly quibble, it's actually a serious
quibble. It's with the words "independently evolved". This suggests
that these populations weren't in contact with each other, but the
hypothesis does not suggest that. What it does suggest is that there did
not need to be any great migration of a newer population of more modern
hominids, but that gene flow would occur throughout the then-populated
world through contact where various populations met. This is easier to
explain with pictures (Milford Wolpoff likes to use a description of
pebbles dropped in water, the ripples all intersecting), but another
possible explanation might be this:
Say you're sitting on one end of a row of people and I'm on the other.
You've got a bag of french fries and I've got a bag of peanuts. We each
share half our snack with the person next to us, and they share half of
what they got with the next person, and so on. Eventually (since we each
have an enormous bag of snack food), everybody has some french fries and
some peanuts. But you've got more french fries than peanuts, and I've
got more peanuts than french fries. We've each got some variation in
the mix of snack food we've got, based on what we started with. But
neither of us has what we we started with (just fries or just peanuts).
Instead we both have the same thing, a salty little mongrel mix of snacks.
Lj> Theory 2 suggests that the
Lj> radiation of earlier hominids occurred just as in Theory 1, but a later
Lj> radiation of "modern" humans from Africa displaced all of the earlier
Lj> varieties.
This theory says that we each have some snacks, but that it's all french
fries from your end of the row, and that what looks like peanuts is
really just little nubs of fries that just resemble peanuts. ;-0
Lj> Does this admittedly simplistic description fairly well
Lj> summarize the current thinking in this field? If so, what sort of
Lj> fossil evidence is there to support each of these theories, and what
Lj> kind of time frame are we looking at for the emergence of modern humans
Lj> in both theories? Thanks for your patience in answering my questions--
Lj> I'm new to all of this!
Lj> --Drew
Both work with the same fossil evidence, and one reason there's such
difficulty resolving the question is that some of the features are
put down to robusticity, which may very well be a trait that is more or
less inherent in hominids, waxing or waning fairly rapidly depending on
diet. (This is the question to ask Wolpoff and Yoel Rak if you're
sitting at a table with them one night; it'd be worth buying the beer.)
Another reason is that we don't have piles and piles of fossils to draw
on. In many species, questions like these can be answered because there
are thousands upon thousands of specimens. Even the existence of
populations living next to each other for a long time, or of any local
population being shown unequivicably to have died out, doesn't
necessarily show what happened overall, since some populations over the
space of almost the entire "Old World" would obviously have died out in
either scenario.
The MtDNA evidence is often used as evidence for the replacement
hypothesis, but this is not correct. First, the MtDNA shows only one
side of the family (it goes from mother to offspring), so it's like
tracing back your lineage using only your mother's side of the family,
then her mother's side, and so on. Doing that could, as a hypothetical
example, show that one is descended from a woman who lived, let's say,
1000 years ago in what is now Tanzania. But would you be considered to
be of African descent? The father of that woman's children could have
been from almost anywhere at that time. Perhaps a visiting Chinese
diplomat on his way back from Italy (it happened). They might have
settled in what is now Indonesia, and their offspring intermixed with
the many many traveling types who passed by or came to live there. You
could be considered by one and all (including yourself) as, say, part
Indonesian and part Dutch, yet your MtDNA, if it could be traced back
with absolute accuracy, would lead to a woman in eastern Africa.
So MtDNA does not show the effects of admixture in a lineage; it's like
tracing back one speck of dust in a single drop of water in a stream.
It tells you where the speck of dust came from (as far as it can be
traced) but it doesn't tell you as much as you'd hope about what parts
of the stream it travelled through.
A note about the multi-regional hypothesis; it tends to be confused with
Carleton Coon's work in the sixties. Coon, I think, was trying to get
across much the same idea or at least explain the same data, but got
bogged down in a naive view of races that's still happening today. That
is, dividing people by region and only some physical characteristics;
the usual skin color, hair type, etc. This led him off course. There
is no particularly good reason to divide people up by skin color instead
of ear wax type, for instance (not to mention the amazing variation and
overlap in the colors we put into different groups).
Jim Moore (j#d#.moore@canrem.com)
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