On evolution / John Maynard Smith.

  • Maynard Smith, John, 1920-2004.
Date:
1972
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: On evolution / John Maynard Smith. Source: Wellcome Collection.

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    I accepted the solution at once, because the phenomenon of complementary base pairing provided a mechanism for gene replication. My point then is that, so far from being regarded as contra¬ dictory to or subversive of classical genetics, the new mole¬ cular ideas were accepted by classical geneticists because they provided a chemical explanation for the basic assumptions of Mendelian genetics. Interestingly, the clearing up of anoma¬ lies in classical genetics was not a major reason for the accept¬ ance of molecular genetics. Thus Kuhn suggests that it is a sign of the coming revolution within normal science that 'anomalies'—that is, phenomena which cannot be explained within the accepted framework — should accumulate. There were of course anomalies within classical genetics in 1952, but they were not immediately cleared up by molecular genetics. Perhaps the most important anomaly was the phenomenon of 'adaptive enzymes', whereby a bacterial strain starts to pro¬ duce a specific enzyme only when the substrate for that enzyme is present, a phenomenon which led Hinshelwood to formulate a non-Mendelian and fundamentally Lamarckian theory of heredity. Adaptive enzymes were anomalous because it seemed that, in contradiction to the Weismannist assumption, an adaptation was being inherited. This phenomenon remained unexplained for some time after the general acceptance of the basic concepts of molecular genetics, and was not fully explain¬ ed until the discovery of 'regulator genes' by Monod and Jacob in 1959. Within evolution theory, molecular biology has raised new problems concerned with the evolution and variation of pro¬ teins, with the evolution of genetic mechanisms, and with the nature of mutation. But it has proved to be an addition to the pre-existing theory rather than a revolution in it. This has been most obviously true for the fundamental Weismannist assumption which underlies neo-Darwinism. In its pre- molecular form, this assumption stated that although genes can influence the development of the body or 'soma', changes in the soma cannot alter genes in an adaptive way. Since 1952, this has been replaced by the 'central dogma' of molecular biology, which states that information can flow from nucleic acids to proteins, but not from proteins to nucleic acids. The correspondence between these two ideas is obvious once it is realized that genes are made of nucleic acid, and that they act 5