Biometrical genetics : the study of continuous variation / K. Mather.

  • Kenneth Mather
Date:
[1949]
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Biometrical genetics : the study of continuous variation / K. Mather. Source: Wellcome Collection.

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    2 THE GENETICAL FOUNDATION ratios, with their clear impHcation of the particulate or discon¬ tinuous nature of hereditary constitution and transmission, depend on the use of characters by which individuals could be classed unambiguously into a few (usually two) distinct groups: they cannot come from continuous variation. Indeed, Mendel himself deliberately neglected such variation in his material, presumably with the clear recognition that it could only have a distracting influence in his analyses. Yet this continuous variation could not be completely over¬ looked. Darwin himself had emphasized the importance of small cumulative steps in evolutionary change, and observation on any living species, especially the most familiar of all, man, showed how much of the variation between individuals луаз of this kind. The genetical problem of continuous variation remained therefore a challenge to geneticists; the more so as biometrically Galton and Pearson had clearly shown such variation to be at least in part hereditary, even although they had failed to discover the mode of transmission. Neither the Galtonian nor the Mendelian method was of itself capable of supplying the solution. The understanding of continuous variation awaited a fusion of the two methods of approach, the genetical and the biometrical, for each supplied what the other lacked. The one gave us the principles on which the analysis must be based; the other showed the way in which to handle continuous variation, the way of representing it in a form which made fruitful analysis possible. Fusion was, however, delayed by a rivalry which arose between Biometricians and Mendelians as soon as Mendel's work was redis¬ covered. This was aggravated by divergent opinions on the import¬ ance of continuous and discontinuous variation in evolutionary change, and acerbated by the polemics of the protagonists. In time, attempts to reconcile the two views became welcome to neither party. The original discordance seems to have arisen because neither side understood the full implications of Mendel's fundamental separation of determinant and effect, of genotype and phenotype. The Biometricians seem to have regarded continuous somatic variation as implying continuous genetic variation, and the Mendelians seem to have considered discontinuous genetic variation as incompatible with anything but obviously discon¬ tinuous somatic variation. Indeed, de Vries took continuity of variation in the phenotype as a criterion of its non-heritability. Two important steps had to be taken, therefore, before the bio¬ metrical and genetical methods could be brought together. In 1909
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