From: epowers@mccoy (POWERS)
Subject: Re: THE MODERN SYNTHESIS
Organization: New Mexico State University
Date: Tue, 26 Jan 1993 23:33:42 GMT

In article <C1BvJ7.9xF@gpu.utcs.utoronto.ca> lamoran@gpu.utcs.utoronto.ca  
(L.A. Moran) writes:

[...]
 The modern theory of the mechanism of evolution
> differs from Darwinism in three important respects:
> 
>      1) It recognizes several mechanisms of evolution in addition
>         to natural selection. One of these, random genetic drift,
>         may be as important as natural selection.
> 
>      2) It recognizes that characteristics are inherited as discrete
>         entities called genes. Variation within a population is due
>         to the presence of multiple alleles of a gene.
> 
>      3) It postulates that speciation is (usually) due to the gradual
>         accumulation of small genetic changes. This is equivalent to
>         saying that macroevolution is simply a lot of microevolution.
> 
> In other words, the Modern Synthesis is a theory about how evolution  
works
> at the level of genes, phenotypes, and populations whereas Darwinism was
> concerned mainly with organisms, speciation and individuals. This is a  
major
> paradigm shift and those who fail to appreciate it find themselves out  
of
> step with the thinking of evolutionary biologists. Many instances of  
such
> confusion can be seen here in the newsgroups, in the popular press, and  
in
> the writings of anti-evolutionists.
> 
> The major controversy among evolutionists today concerns the validity of
> point #3 (above). The are many who believe that the fossil record at any  
one
> site does not show gradual change but instead long periods of stasis  
followed 
> by rapid speciation. This model is referred to as Punctuated Equilibrium  
and 
> it is widely accepted as true, at least in some cases. The debate is  
over
> the relative contributions of gradual versus punctuated change, the  
average 
> size of the punctuations, and the mechanism. To a large extent the  
debate is 
> over the use of terms and definitions, not over fundamentals. No new 
> mechanisms of evolution are needed to explain the model.
> 
> Some scientists continue to refer to modern thought in evolution as
> Neo-Darwinian. In some cases these scientists do not understand that the
> field has changed but in other cases they are referring to what I have
> called the Modern Synthesis, only they have retained the old name.
> 
> 
> Laurence A. Moran (Larry)

	Is this really a discussion of the mechanism of evolution or the  
rate?  The rate will definitely depend on the mechanism, but I think  
you've spoken almost entirely of the rate, not the mechanism.
	The major difference that I see in the field today is Mayr's view  
of speciation vs. Dobzhansky's (which could be thought to include Mayr's).   
Mayr said simply that speciation was a side product of geographic  
isolation (The founder effect).  Dobzhansky's problem with Mayr's idea was  
that there would be no selective advantage to reproductive isolation  
(speciation) just because of geographic isolation.  He believed that there  
was an  initial separation of populations and some adaption to their  
environments.  The two populations then might come together and begin  
hybridizing.  If there had been enough adaption that the hybrids were less  
fit, those organisms unable to mate with heterospecific organisms (or even  
better, able to distinguish between conspecific and heterospecific  
individuals) would have a big competitive edge.  Eventually, the two  
populations would become completely isolated reproductively.
	A not-so-minor variation on Dobzhansky's ideas has recently been  
proposed by my boss, DJ Howard at NMSU. (I mention it for interest,  
mostly.  I'm sure others have also come up with variations I don't know  
about).  His idea is that hybrid zones act as a "species pump", in which  
new species arise from all sorts of weirdness that happens in mosaic  
hybrid zones.  If you're interested, I can post or email you some  
references on this sort of thing.
					Erik Powers