[Marxism] human origins

Paul pgallagher4 at nyc.rr.com
Fri Aug 12 13:44:52 MDT 2005


Charles Brown wrote:

>
>I believe the Mayr theory is that two populations that are still gondally
>capable of mating fertily are geographically ( "patrically" meaning country)
>and thereby physically separated and unable to mate because of this physical
>separation, not because of organic incompatibility. But that this
>geographical separation eventually leads to physiological inability to mate
>fertily.
>  
>
Yes, in Mayr's view, speciation is a kind of side-effect of geographic
isolation.

>Seems to me that the big thing biology wants to find out is how is it that
>populations lose the physiological ability to mate fertily with each other.
>This is the big mystery of speciation. Mayr's theory is sort of , excuse the
>expression, the "ground" that sets up the more fundamental reproductive
>incomptability that is physiological.
>  
>
One idea he proposed is that is was a consequence of small population size.
Simply by random sorting processes, the isolate becomes reproductively
incompatible with the parent population. Additional isolating mechanisms
might evolve later when the isolate resumes contact with the parent 
population.
In that case, there would be selection for reproductive isolating 
mechanisms.

However, all of this remains controversial, 60 years after Mayr. Mayr's 
ideas
were for a long time the orthodoxy, but increasingly there was evidence of
other modes of speciation, in which species arose without geographic 
isolation.
Chung-i Wu takes a very strong position against Mayr, and Mayr replies here:
http://www.blackwellpublishing.com/journals/jeb/
http://www.blackwellpublishing.com/specialarticles/jeb342.pdf
http://www.blackwellpublishing.com/specialarticles/jeb336.pdf

>I also wanted to throw out the thought that it is important to note that
>though there are , empirically, fewer new traits arising in the equilibria
>than in the punctuations, there _are_ new traits arising in equilibria, no ?
>The equilibria are "dynamic stabilities". Some of these arise by selection
>and some don't (following Gould's general approach). Some are spandrel-like,
>some are genetic drift, some are not originated as adaptions, but are
>adapted to being adaptions after they arise by non-adaptive causes ( snails
>gets shells through adaptive processes; there is space under the shell as a
>"spandrel"; then the spandrel is used to store eggs, which activity _is_
>adaptive; so not-adaptive in origin , but adapted to being adaptive post
>hoc; I don't know whether the shell arises in speciation/punctuation or in
>an "equilibrium" phase)
>
>But the main point I am making is that there are new traits that arise in
>the non-speciating phases even if fewer and of non-qualitative type changes,
>with qualitative change defined as speciating.
>
>Also,no doubt, there is some speciation in "equilibria" and some non
>speciating changes in "punctation" periods, empirically.
>
>  
>
Yes, in a way it's paradoxical. We observe the great deal of variation 
in natural populations,
and we know that new variation continuously appears through mutation and 
recombination,
but when we look at the fossil record, the overwhelming pattern is of 
stasis -- species remaining
more or less unchanged for hundreds of thousands of years -- and 
similarly, when we look at living
populations, we see not a continuous band of variation, but organisms 
grouped discretely as
species. It points to the existence of species as real, cohesive 
entities -- they cohere over their
geographic range and over vast expanses of time. There are certainly 
exceptions, but that
seems to be general rule, in my opinion.

Paul





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