The selectionist/neutralist controversy has continued for nearly 40 years, and a resolution is not in sight. NeoDarwinists like to think that Neutral Evolution is compatible with neoDarwinism, but this is a bit like their attitude to Punctuated Equilibrium: everything worth saying has to be compatible with neoDarwinism! Meanwhile, the controversy goes on. . .
In a recent PNAS review paper, Masatoshi Nei argues that our knowledge of genetics is such that, as far as genes controlling phenotypic characters are concerned, conservation is a more applicable description than evolution. "Phenotypic evolution occurs primarily by mutation of genes that interact with one another in the developmental process. The enormous amount of phenotypic diversity among different phyla or classes of organisms is a product of accumulation of novel mutations and their conservation that have facilitated adaptation to different environments. [. . .] It appears that the driving force of phenotypic evolution is mutation, and natural selection is of secondary importance."
This is, of course, not the message that you get from neoDarwinists, who continue to emphasise adaptive causation. In their view, natural selection is essential to explain the origin of complexity, and they are not impressed by the neutralists diminishing of the role of natural selection.
Whilst this paper can be discussed in various ways, I want to focus on the educational issues. We have here a controversy about the relative significance of mutations and natural selection. It is not a minor matter. NeoDarwinists feel very strongly about it. Take, for example, Richard Dawkins critiquing Michael Behe in The New York Times (July 1 2007):
The crucial passage in The Edge of Evolution is this: "By far the most critical aspect of Darwin's multifaceted theory is the role of random mutation. Almost all of what is novel and important in Darwinian thought is concentrated in this third concept."
What a bizarre thing to say! Leave aside the history: unacquainted with genetics, Darwin set no store by randomness. New variants might arise at random, or they might be acquired characteristics induced by food, for all Darwin knew. Far more important for Darwin was the nonrandom process whereby some survived but others perished. Natural selection is arguably the most momentous idea ever to occur to a human mind, because it - alone as far as we know - explains the elegant illusion of design that pervades the living kingdoms and explains, in passing, us. Whatever else it is, natural selection is not a "modest" idea, nor is descent with modification.
Then compare with Nei, who says this:
Although this type of statement is quite common in the evolutionary literature, it is obvious that any advantageous genotype is produced by mutation including all kinds of genetic changes. Natural selection occurs as a consequence of mutational production of different genotypes, and therefore it is not the fundamental cause of evolution.
This is an issue which is educationally very important, and it also happens to be relevant to ID arguments. It is not in the educational interests of students to prevent such issues being discussed by teachers, and nor should it be deemed a "religious intrusion" into science when neoDarwinism is subjected to critical scrutiny.
The new mutation theory of phenotypic evolution
Proceedngs of the National Academy of Sciences, USA, July 24, 2007, 104(30), 12235-12242 | doi 10.1073/pnas.0703349104
Recent studies of developmental biology have shown that the genes controlling phenotypic characters expressed in the early stage of development are highly conserved and that recent evolutionary changes have occurred primarily in the characters expressed in later stages of development. Even the genes controlling the latter characters are generally conserved, but there is a large component of neutral or nearly neutral genetic variation within and between closely related species. Phenotypic evolution occurs primarily by mutation of genes that interact with one another in the developmental process. The enormous amount of phenotypic diversity among different phyla or classes of organisms is a product of accumulation of novel mutations and their conservation that have facilitated adaptation to different environments. Novel mutations may be incorporated into the genome by natural selection (elimination of preexisting genotypes) or by random processes such as genetic and genomic drift. However, once the mutations are incorporated into the genome, they may generate developmental constraints that will affect the future direction of phenotypic evolution. It appears that the driving force of phenotypic evolution is mutation, and natural selection is of secondary importance.
Dawkins, R. Inferior Design, The New York Times, July 1, 2007 [for link, go here]
Scordova, Prominent NAS member trashes neo-Darwinism, Uncommon Descent, 18 July 2007
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