Heredity / by J.A.S. Watson.

  • Watson, James A. S. (James Anderson Scott), 1889-1966.
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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    26 HEREDITY conditions more or less abnormal, such as deficient food, exceptional exercise of a particular member, dis¬ ease, mutilation, &c., acquired characters would be produced. If we could take a pair of identical twins, and separate them at birth, giving the one fresh air, abundant food and exercise and education, and rearing the other amid the unhealthy and degrading conditions of our slums, the differences, which would certainly be enormous, would be altogether modification differences. If, on the other hand, we could take two children of different parentage, and rear them under exactly the same conditions, the differences between the two would be altogether inborn. In practice it is not always possible to distinguish inborn from acquired characters, even when we know fully the conditions under which the organism has lived. But theoretically the distinction between what is bom and what made, is absolute. We may now turn to the inborn variations and en¬ deavour to see how they arise. How does an organism come to differ from its parents, or from the mean of its parents, if it has two, with regard to its inborn char¬ acters ? It seems certain that the great majority of inborn differences between parent and offspring are due simply to new combinations of previously existing characters. It is easy to see that with sexual reproduction, where two parents are involved in the production of the offspring, there is a continual mixing of different germ plasms, and thus almost infinite chances of new com¬ binations. By way of illustration, we may suppose four sacks of marbles of different colours, say white, black, red, and yellow respectively, to represent the respective germ plasms of four individuals. By mixing the black with the white and the yellow with the red, we get something corresponding to two new germ plasms. If now we take random samples from each lot, say half-a- dozen at a time, and mix the sample from the one lot