Posted by
Nick Thompson on
Jan 25, 2005; 5:05pm
URL: http://friam.383.s1.nabble.com/Help-with-inheritence-tp519985.html
Dear Friamers,
Everything that you-all are having me read undermines the notion of natural selection. But it does so by undermining genetic inheritance, the idea that because of genetic material passed from parent to offspring, offspring will differentially resemble. I would have thought that of all the premises on which natural selection was based, the premise of family resemblance was the most secure. I have two questions, Does complexity have an alternative theory of inheritance? Does complexity have an evolutionary theory in which inheritance plays not significant part?
The full text of my rumination on this subject follows:
It has become a standard critique contra the neo-Darwinist synthesis that it is based on an unrealistic, over-simplified, and perhaps ideologically based view of molecular genetics and development. Books by Margulis, Caporale, Elldredge, Gould, and others emphasize the great complexity of the events that take place in the creation of the gamete genome, in the growth and development of the cells subsequent to fertilization, and in the day-to-day production of protein products by the bodies cells. Some authors scoff at what they call the bean-bag genetics of neo-Darwinist and its gratuitous assumption that the genome consists of a set of mutually independent, randomly reassorting heritable units. The critique cannot be ignored: The simple fact of chromosomes would seem to render such a conception absurd, even if one ignored the recent discoveries of high levels of interaction among elements of the nuclear genome and between that genome and the mitochondrial genome during cell division.
But exactly how is the above critique a critique of Darwinism. Darwins theory is stated in the form of a hypothetical, a series of conditions which if met lead to adaptation and evolution. We are thus led, by affirming the consequent, to the conclusion that these conditions are the cause of adaptation and evolution. The conditions are:
(1)If the reproductive potential of the members of a species is greatly in excess of the capacity of their worlds to support them
AND
(2) The members of this species vary in the possession of traits
AND
(3) Those traits are heritable (i.e., they are possessed differentially by the offspring of individuals that bear them)
AND
(4) some of these traits offer an advantage in the struggle for existence implied by (1)
THEN
(5) traits of the type mentioned in (4) will in time come to characterize the species producing adaptation of the species to the conditions of its existence. This process, applied to many species, will in time produce evolution, since evolution is just (on my account) the fact that over history, different species have tended to adapt to their different conditions of existence.
Like all cumulative chains of premises, natural selection theory is a logical chain which depends on ALL of its elements for its logical success. In other words, if any of the 4 premises above is false, than natural selection as understood by Darwin cannot occur. Which of the premises of natural selection does the developmentalist attack. Surely not the Malthusian Premise, Premise (1). Nor also the variational premise (2) nor the reproductive advantage premise (4). The developmental critique is in fact an attack on the inheritance premise. But the inheritance premise is the only one of the four that is NOT a hypothetical. It is often said that Darwins explanation of inheritance was very bad, and got worse as he elaborated it through the several editions of the Origin. But his knowledge of the FACTS of inheritance was very secure: Darwin knew from close personal experience and avid reading that inheritance of traits from parents to offspring was a possibility. And a century of research in breeding and hybridization in plants and animals has not diminished our confidence that (at least) some traits can be differentially represented in parents and offspring. For the developmental critique to succeed in its attempt to undermine Darwinism, it must do so by undermining not the theory of inheritance, but the fact of inheritance, and that fact would seem to be the most secure of Darwins premises.
True, undermining the fact of inheritance would have a devastating effect on natural selection theory. If natural selection is to work, then the parents have to serve, in effect, as representations of the offspring. It must be true that decisions to breed or not to breed parents, based on their phenotype, must be reflected in the phenotypes of the offspring in the next generation. Any developmental process that interferes with this representation from parental to offspring generation, interferes with natural selection. Mutation interferes with natural selection. Dominance and epistasis interfere with natural selection. Genomic imprinting interferes with natural selection. Horizontal transfer of genes from other organisms would interfere with natural selection. Environmental muting or triggering of traits interferes with natural selection. In fact, to the extent that any mechanism interferes with the isomporphism between variations in the parental generation and variations in the offspring generation, that mechanism interferes with natural selection. It does so only because it interferes with inheritance.
So let is grant for the moment that the main challenge of developmentalists for natural selection theory is a challenge against Mendelism, not a challenge against Darwinism. Does complexity theory have anything to offer to mitigate this challenge. Is there a complexity variant of inheritance theory?
Nicholas S. Thompson
Professor of Psychology and Ethology
Clark University
[hidden email]
http://home.earthlink.net/~nickthompson/[hidden email]
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