Does microevolution logically include macroevolution?

This is some "background" information from which I will draw on and comment on later in thie thread.Second below is the section in Mayr’s biophilosophy book BEFORE he has the heading “Microevolution and Macroevolution” where in there he wrote,

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The classical view of macroevolution held by Darwin and the majority of paleontologists up to the present day is that species, in the course of their gradual evolution in time, change to such a degree that they will become different genera , or taxa of still higher rank, and acquire in the process all the adaptations and specializations of the world of organic diversity. Viewing evolution strictly in the vertical dimension, as was done by most paleontologists including Simpson . This lead Gouldschmidt to his theory...These are inevitable connections between the phenomena studied by mathematical population geneticists and those macroevolutionary processes that are studied by paleontologists and comparative anatomists.

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Such a connection can be established, however, by making use of the findings of population systematics, and of the horizontal approach to evolution, as studied by the new systematics, because they provide a perfect bridge between micro- and macroevolution. Rudiments of this demonstration can be found in Rensch’s writings and in my 1942 book.

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Genetic Milieu

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For the last 60 years - but one could say all the way back to Darwin (1859:11, 146; 1868 II:319-335) - two traditions of viewing the genotype can be distinguished. According to the anatomistic (“beanbag”) view, each gene is independent not only in its actions but also in the effects of selection on it. Evolutionary stasis of the phenotype, for instance, is explained by the stabilizing selection acting on individual genes. According to the holistic (integrative) view, genes perform as teams, and large numbers of other genes form the “genetic milieu” (Chetverikov 1926) of any given gene. Gene exchange at any locus may have an impact on the selective value of genes at other loci. Even though the atomists (reductionists) are fully aware of pleiotropy, polygeney, and other processes that produce the phenotype ( the target of selection) and that automatically result in a selectional interaction of genes, they ignore these processes in their evolutionary interpretations. Those others, however, who have stressed the genetic milieu (Chetverikov), genetic homeostasis(Lerner), internal balance(Mather), or the cohension of the geneotype (Mayr) have consistently looked at the impact of natural selection in a different way from those for whom the role of genes is essentially additive. The atomists, for instance, would treat developmental constraints and stabilizing selection as two separate problems , while for the “holists” the major cause of stabilizing selection is precisely the set of developmental constraints generated by the cohesion of the geneotype. Schmalhausen was fully aware of this, but the majority of geneticists, particularly the mathematical geneticists, ignore it because it makes calculations “messy.” Indeed, there is still no adequate methodology to analyze the controlling factors of cohesion.

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The holists, thus , have introduced on major new factor into evolutionary theory, the internal structure of the genotype. They claim that much of macroevolution cannot be explained by atomistic gene replacements or by selection pressures on single genes but only by a more or less drastic reorganization of the geneotype made possible by loosening up the tight genetic cohesion of the geneotype that characterizes widespread populous species. (I should not say new because Darwin already defended such a viewpoint and it has been suggested again and again, almost invariably by evolutionists from the naturalist’s camp, although those who came to evolution via embryology, like Waddington and Goldschmidt, have expressed similar ideas.)

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No one has made a stronger case in favor of the theory that a loosening up of the cohesion of the geneotype is an important and perhaps the decisive component in much of speciation than Carson (1975). His arguments powerfully support similar arguments made by authors from Darwin to Rensch, Lerner, Waddington, Mayr, and others.

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Unless I go back to Mayr’s original citation of Hampton Carson’s work, I shall likely be referring populationally, no matter the classification to ,

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The present discussion embraces all such shifts, although the emphasis will be placed on the radical departures. Profound changes such as the latter would be the type of change most conducive to the action of the genetic phenomena to be described. The ascending phase of population growth will be referred to as a “flush” and the subsequent fall as a “crash.” These terms will serve to emphasize the point, which will be made later, that crucial alterations in gene pools most likely to occur whenthe changes have the precipitate nature suggested by these rather dramatic terms.

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p123 in Population Biology and Evolution by HLCarson.One can get at the "logics" rather quickly if one concentrates on Mayr use of "constraint set" 'developed' but I do not think it generally a good pedagogical idea to go this far nonequilibrial wise to start discussing where Mayr had to seperate out Gouldschmidt rather than the language of mutations.
Error 404: Page Not Found | Harvard University PressThis message has been edited by Brad McFall, 09-21-2005 04:20 PM