Neo-Darwinism / R.J. Berry.

  • R. J. Berry
Date:
1982
Catalogue details

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

Credit: Neo-Darwinism / R.J. Berry. Source: Wellcome Collection.

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    BIOMETRICIANS AND MENDELIANS 11 Gallon's ideas were seized on by a mathematician, Karl Pearson, and by W. R. Weldon, who was Professor of Zoology at University College London and then Oxford. Weldon realized the importance of Gallon's work for evolution, since the frequency of deviations from the type could be measured and associations measured. He believed that 'the questions raised by the Darwinian hypothesis are purely statistical, and the statistical method is the only one at present obvious by which that hypothesis can be experimentally checked', and co¬ operated with Pearson in seeking methods to test and extend Gallon's law. They persuaded the Royal Society of London to establish in 1894 an Evolution Committee 'for the purpose of conducting statistical enquiries into the variability of organisms', and this committee sponsored work on the death-rates of crabs in Plymouth Sound, and measurements of herring and of ox-eyed daisies. In 1897 the Evolution Committee was joined by William Bateson, a Cambridge zoologist and first director of the John Innes Institute (1910-1926). Bateson was convinced of the importance of discontinuity in evolution, and dubious about the early work of the Committee. He criticized Weldon for measuring crabs at different stages of moult. He rapidly brought about a change in the approach of the Committee, and in 1900 Pearson and Weldon resigned. Meanwhile the search for a better understanding of the genetical process led in 1910 to the rediscovery of Gregor Mendel's work originally pubhshed in Brno, Czechoslovakia in 1866 by the botanist de Vries in Holland, von Tschermak in Austria, and Correns in Germany. Mendel's main conclusions (the regular segregation and independent assortment of inherited traits) were soon con¬ firmed in animals by Bateson and Punnett in Cambridge and Cuénot in Paris. The application of Mendelian ideas had two important consequences for evolutionary ideas: they indicated that inherited factors did not blend, but persisted unchanged through the generations, thus removing the chronic problem of variation loss; and they appeared to show that inherited variation was discontinuous. In reaction the biometricians (i.e. Pearson and Weldon) regarded Mendelism as a threat. The six years following the rediscovery of Mendelism (until the death of Weldon in 1906) witnessed increasingly bitter confrontations between the Mendelians and biometricians over 'homotyposis' (Pearson's attempt to weld together heredity and differentiation), mutation theory, the meaning of genetical dominance, etc. The physical basis of heredity was not generally accepted until the work of T. H. Morgan and his colleagues on sex determination, linkage, and mutation in Drosophila melanogaster linked breeding results with cytological knowledge (summarized in The Mechanism of Mendelian Heredity, published in 1915). However, Mendel's 'laws' (Mendel himself did not state any laws, but his conclusions are most easily summarized in this way) were everywhere being confirmed, and the Mendelians increasingly gained the upper hand. The biometric-Mendelian controversy degenerated into personal conflict, and ended when Weldon died of pneumonia at the age of 46. but the split between the supporters of continuous and discontinuous evolution continued to grow, and was only resolved in the 1930s (section 1.5).
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