[Marxism] Re: human origins
pgallagher4 at nyc.rr.com
Wed Aug 10 20:46:08 MDT 2005
>CB: I think you focus in on some key questions here.
>Isn't the problem answered somewhat by the fact that there can be a
>accumulation of many, many new traits in a population of a species ( a
>population that is reproductively isolated from other populations of the
>species), but a new species is not "originated" until a new trait arises
>that ends the ability of that population to produce viable and fertile
>offspring with other populations of the species. This is pretty much
>to be a relatively "sudden" or "punctuating" event in the overall time
I think this is something of a non-problem. People frequently bring
up this point, but there's a good deal of evidence that speciation
and the acquisition of distinct characteristics, at least in animals,
are usually coincidental.
For example, Gould discusses Cheetham's study of bryozoans:
In a second study (Science, vol. 248, 1990), Jeremy Jackson and Alan
Cheetham studied eight species in three genera of bryozoans. These
colonial marine organisms are so highly variable, and supposedly
so subject to immediate shaping by nongenetic forces (temperature,
crowding, and so on), that many biologists have doubted any
correspondence between morphological package and true biological
species and have even doubted that morphological packages
could be specified at all. But Jackson and Cheetham, in a series
of carefully controlled experiments, first determined that they
could find no cryptic species within any of the packages
(coincidence of morphological and biological species). They then
grew two generations of the species in a common environment to
see if the morphological distinctions were truly inherited or
merely a transient result of growing in certain places under
certain conditions. Each package checked out as genetically
distinct and morphologically unique and stable. They conclude:
Our results show that the identity of quantitatively defined
morphospecies of cheilostome bryozoans is both heritable and
unambiguously distinct genetically. . . . Thus, cheilostome
morphospecies appear to be good biological species.
Here are some more worthwhile books and papers:
The Fall 1994 Paleobiology and the
Dec. 20 1996 issue of Palaeogeogrphy,palaeolclimatology, and Palaeoecology.
Gould and Eldredge's "Punctuated equilibrium comes of
age," Nature 366: 223-227, Nov. 18 1993.
Macroevolution: Pattern and Process, by Steven Stanley.
The New Evolutionary Timetable : Fossils, Genes, and the
Origin of Species, by Steven Stanley.
Causes of Evolution: a Paleontological Perspective, edited by Robert
Ross and Warren Allmor.
Speciation and its Consequences, edited by Daniel Otte and John Endler.
Tempo and mode in evolution : genetics and paleontology 50 years after
Simpson / Walter M. Fitch and Francisco J. Ayala, editors.
Evolutionary paleobiology : in honor of James W. Valentine / edited by
Jablonski, Douglas H. Erwin, and Jere H. Lipps.
Causes of evolution : a paleontological perspective / edited by Robert M.
Ross and Warren D. Allmon.
New approaches to speciation in the fossil record / edited by Douglas H.
Erwin and Robert L. Anstey.
Times Frames, Unfinished Synthesis, Macroevolutionary Dynamics,
and other books by Niles Eldredge
Bokma, F. (2002) Detection of punctuated equilibrium from
molecular phylogenies. J. Evol. Biol. 15: 1048-1056.
"How nature Works," by Par Bak.
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