Page:Popular Science Monthly Volume 67.djvu/199

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THE

POPULAR SCIENCE

MONTHLY

 

JULY, 1905.




RECENT DISCOVERIES IN HEREDITY AND THEIR BEARING ON ANIMAL BREEDING.[1]
By Professor W. E. CASTLE,

HARVARD UNIVERSITY, CAMBRIDGE, MASS.

EVERY breeder of animals is familiar with the great complexity of hereditary processes. He knows that characters of the most varied sorts are inherited. These relate not only to general size and proportions, but also to the structure of individual parts; and not merely to structural, but to functional peculiarities as well. Thus, in certain races or strains of animals, we find inherited great fecundity, or early maturity, or ability to put on fat, or to produce abundant milk; in other cases, speed, keen scent, fierce or gentle disposition, and numberless other characteristics are plainly inherited. Very rarely are any two heritable traits necessarily associated. The cow with a good flow of milk may or may not be gentle; the keen-scented dog may or may not be speedy. Accordingly, we must conclude that different hereditary characters are inherited independently of one another, and are probably represented by different structural elements in the sexual element or germ. We know, further, that the laws of transmission of different characters are different, so that we can not estimate the force of heredity in the lump, but must fix our attention on one character at a time if we wish to analyze the complex processes in operation.

Francis Galton (1889) was the first to recognize that in the case of certain characters the result of inheritance is a blend of the conditions


  1. Published by permission of the Carnegie Institution of Washington, to whose officers the author is deeply indebted for aid in the prosecution of his studies, and in particular for the loan of figures 4–14 of this article.