Re: chimps on the savanna? Nooooo.....
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Sun, 29 Oct 1995 13:12:21 GMT
hubey@pegasus.montclair.edu (H. M. Hubey) wrote:
>>Within the framework of punctuated equilibria this may be right,but this
>>idea is still controversial.
>Why is the idea that large scale changes can take place in
>small populations quickly controversial?
I said that the idea of *punctuated equilibria* is still controversial in
reply to Paul Crowley's:
>>My understanding of general evolutionary priciples is that during the
>>process of speciation there will be very rapid adaption by the small
>>group (<300 ?) involved in making the change, but that once the
>>species has found its niche, established its new form of life, become
>>successful and expanded both in numbers and territory, the change
>>will be minimal.
I doubt this is seen as a "general evolutionary principle".
Some population geneticists argue that the founder effect is usually
ineffective in shifting populations to new adaptive peaks.
A small population (<300) has serious problems of inbreeding and genetic
drift which may not be adaptive at all.
And what may seem rapid from a geological point of view,may take several
thousand generations in reality,and even then the changes in morphology are
usually not dramatic.
"In all the documented and proposed cases of punctuated equilibria,the new
form that apparently originated rapidly differs from the original ancestral
form in only rather subtle ways,such as shape or the number of lenses in
the compound eye of trilobites." (D.Futuyma.1995,_Science on Trial_ p.262,)
>>It can be an artifact caused by a coarse fossil record.
>Maybe there's no need to refer to the fossil record.
Maybe not,but the idea,as proposed by Stephen Gould and Niles Eldredge,was
mainly based on observations of the fossil record.In a coarse fossil record
new species seem to appear quite suddenly with virtually no evidence of
transitional forms,and after their initial appearance show little
substantial change.
However,as the record becomes more complete transitions take on a more
gradual character and there seems to be more fluctuation in morphology.
(but there are exceptions)
Gerrit.
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