THE 



POPULAR SCIENCE 



MONTHLY. 



JULY, 1905. 



RECENT DISCOVERIES IN HEREDITY AND THEIR 

 BEARING ON ANIMAL BREEDING.* 



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, Ave 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 num- 

 berless 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 clog 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 hi end of the conditions 



* 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. 



VOL. LXVI.-13. 



