Evolution now : a century after Darwin / edited by John Maynard Smith.

Date:
1982
Catalogue details

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

Credit: Evolution now : a century after Darwin / edited by John Maynard Smith. Source: Wellcome Collection.

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    INTRODUCTION 3 processes leading to evolutionary adaptation, becomes the only process (at least, until the evolution of organisms sufficiently intelligent to leam from their parents). The next important step was the rediscovery of Mendel's laws at the start of this century, and the formulation of the chromo¬ some theory of heredity. The first impact of Mendelism on evolu¬ tionary biology was distinctly odd. The early Mendelians saw themselves as anti-Darwinians; Darwin's banner was held aloft by the biometrie school, who concentrated on measuring the correlations between relatives, and who regarded genes as meta¬ physical entities. The Mendelians saw the 'mutations' they studied as each being the potential starting point of new species, and the continuous variation studied by the biometricians as evolu- tionarily irrelevant; the biometricians saw mutations as patho¬ logical deviants doomed to early elimination by selection, and continuous variation as the stuff of evolution. The argument, led by Bateson on the one side, and Pearson on the other, fore¬ shadowed the current debate between punctuationists and gradualists, discussed below. It is part of the larger debate be¬ tween those who see the world as continuous and those who think it proceeds in jerks. The debate, at least in the form in which it then presented itself, was largely settled by the work of the population geneticists. Fisher, Haldane and Wright. Two points were made clear. First, the continuous variation studied by the biometricians could be explained by alternative alleles at many loci, each by itself having a small effect on the phenotype. Second, even rather small dif¬ ferences in fitness between genotypes are sufficient to determine the direction of evolutionary change, despite mutation being mainly in an opposite direction. The work of the population geneticists prepared the way for the 'modem synthesis' of evolutionary biology, developed in the period 1930-1950 by a group including Dobzhansky, Ford, Julian Huxley, Mayr, Muller, Rensch, Simpson and Stebbins. It is hard in a few sentences to describe what these men did. In effect, they showed that the 'neo-Darwinian' mechanism—natural selection in Mendelian populations—was sufficient to explain the evolu¬ tionary process as it could be observed in nature. Dobzhansky, Ford and others measured genetic variability and natural selec¬ tion in wild populations. Mayr and Rensch (for animals) and Stebbins (for plants) studied geographical variation within and between species, and discussed how new species might arise. Simpson argued that the fossil record could best be understood in
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