Re: Alex's gibbon-like CA
Phil Nicholls (pnich@globalone.net)
Sun, 12 Nov 1995 19:41:24 GMT
Paul Crowley <Paul@crowleyp.demon.co.uk> graced us with the following
words:
>In article <47t3n1$o5e@geraldo.cc.utexas.edu>
> aduncan@mail.utexas.edu "Alex Duncan" writes:
>> Nonetheless, when large-scale climatic
>> changes happen to coincide with numerous speciation events (as has been
>> demonstrated for the African Neogene), it is tempting to speculate that
>> significant evolutionary change and change in habitat are somehow
>> correlated.
>IMO the source of the temptation rests on a common error, probably
>derived from human experience - "there were adverse circumstances
>so we adapted to cope with them".
Tell me something, Paul, where did you learn evolutionary biology? I
am asking this because your version seems so strickingly different
from what the rest of us seem to have learned.
Alex is talking about two observations about the past that seem to
coinside. His conclusions are pretty much consistent with recent
developments in evolutionary biology. Are you familiar with the work
of Elizabeth Vrba?
>There are two sorts of evolutionary change and this error confuses
>them: (a) where the species gets split by a geographical feature or
>environmental change and gradually drifts apart, as we see with
>chimps, gorillas and orangs within the last 2Myr; and (b) where a
>small group establishes a new ecological niche, for which it will
>need a relatively short period of isolation.
Once again, I don't know where you are gettting this. Some of it
sounds somewhat familar but only at a very superficial level. The
only aspects of evolution in which population size is a critical
factor are random genetic drift and founder effect. Small population
size also figures into punctuated equilibrium in that the peripheral
populations that form the basis of new species are small relative to
the core area populations.
In (a) abov, geographical isolation will alter the geographic range of
the species involved. Thus it is occupying a new niche.
Environmental change will also result in a new ecological niche. The
only difference between (a) and (b) then is that you are less specific
in (b) as to what aspects of the organisms niche is new and that the
size of the population is initally small.
Now it is very likely that small populations requirre a shorter period
of reproductive isolation for speciation to occur, which is an
argument punctuationalists make.
>I think that we are agreed that hominid speciation resulted from
>the second mechanism.
You haven't clear outlined a mechanism.
>Do you also agree that climatic change (especially an adverse one) is unlikely to have
>been a factor?
No one said anything about "adverse" changes. It is unlikey that any
major evolutionary change takes place in the without environmental
change.
>BTW I keep seeing the "evolution forces" error everywhere, and it
>drives me bananas. Today's UK Times has a report from Dr Charles
>Goodhart of Cambridge Univ stating the some h.s.s. were "forced"
>by climatic change to move south around 70kya. (It's only a news-
>paper report so I may be being unfair to him - but it is typical.)
>My point is that such change is slow in terms of a hominid lifetime.
>No h.s.s. packed his bags and said "Brrr, it's getting cold, let's
>go to Egypt this winter". It's a tempting scene, but it could not
>be more wrong.
Ahhh!!!!! Now I get it. Your a literalist! Think, Paul. 70,000
years ago. Europe. Ice Age. What do you think Dr. Goodhart might
have been referring to?
>There is supposed to be very rapid global warming happening now.
>Have you heard of any mass movements of any species being "forced"
>north? Yet this is how it's imagined in the African Neogene!
The change to which Alex is referring took place over a period of
several million years, Paul.
Phil Nicholls pnich@globalone.net
"To ask a question you must first know most of the answer"
-Robert Sheckley
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