Heredity / by J.A.S. Watson.

  • James Anderson Scott Watson
Date:
[1912]
Catalogue details

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

Credit: Heredity / by J.A.S. Watson. Source: Wellcome Collection.

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    CHAPTER II VARIATION If it were an absolute fact that like begets Hke, instead of a general tendency, it is apparent that there would be no science of heredity at all. АД the individuals of a race would be identical in tjrpe, and heredity would offer no problem except that of accounting for this identity by some satisfactory theory. But it is a trite observation, which we need not linger to enlarge upon, that no two things in nature are ever exactly ahke. Before entering into the ques¬ tion of how or to what extent these differences are inherited, it is necessary that we should gain some insight into their nature and causes. In this connection, our first task must be to find some method of describing accurately and brieñy such variations as are found. In certain cases this is a very easy matter. Suppose, for instance, that we wished to describe the variation in colour in a certain breed of horses. АП that we have to do is to count the number of bays, blacks, greys, &c., occurring in a group of individuals taken at random, and to state the numbers of the respective colours. In this case we are deahng with material which is at once separable into definite natural groups. The colour does not vary by minute stages from black to white, but the variation is, as we sav, discontinuous. With regard to a great many characters, however, variation is continuous. As regards stature, for in¬ stance, men are not separable into so many definite types, but there is a fairly regular gradation in size, from the giant to the dwarf. How are we to measure and represent variation of this kind ? 18