Decembeb 19, 1913] 



SCIENCE 



887 



In discussing the second factor, the quality 

 of milk yield, the author describes an experi- 

 ment conducted by Count Ahlefeldt, wherein 

 Red Danish cattle, with an average yield of 

 3.42 per cent, milk, were crossed with Jerseys 

 averaging a yield of 5.22 per cent. milk. The 

 hybrid offspring averaged a yield of 4.15 per 

 cent. These cross-bred animals were bred back 

 to the parental Jerseys. The author points 

 out that if quality of yield behaves in Men- 

 delian fashion, one half of the animals, re- 

 gardless of their other traits, would yield milk 

 of Jersey quality, and one half of them would 

 yield the cross-breed quality. Analyzing the 

 table given by the author, we find that of the 

 15 offspring of such matings 7 yielded 4.Y per 

 cent, or richer milk, and 8 yielded below this 

 quality. K the types of offspring from the 

 Cross by Bed Danish, and Cross by Cross ma- 

 tings approximate as closely to the Mendelian 

 expectation as the Cross by Jersey mating just 

 described, and the matings are extensively 

 made, then, even though yield may be gov- 

 erned by a host of unit traits, they would ap- 

 pear, for practical purposes, to move in syn- 

 chronism, and the practical breeder would 

 have a working principle of value. One would 

 suspect, however, that such a complex thing 

 as quality would shatter in the subsequent in- 

 breeding of hybrids. More data are required. 



The author points out that yield of butter is 

 not a fair basis for breeding selection, because 

 butter yield is dependent upon two factors, 

 namely, quality and quantity of milk. Each 

 one of these factors should be taken as a basis 

 for selection, and a combination of high qual- 

 ity and high yield sought by Mendelian meth- 

 ods. He sees no sound reason why high qual- 

 ity and great quantity of yield should be 

 mutually exclusive; he believes they can be 

 combined by Mendelizing. 



If any adverse criticism were to be rendered, 

 it must be said that throughout the book the 

 author disregards the exceptions to the rule 

 when describing the heredity of an animal 

 characteristic which appears to approximate 

 Mendelian expectation. For instance, con- 

 tinual reference is made to color inheritance 

 in Shorthorn cattle, assuming the case exactly 



parallel to that of the Andalusian fowl, 

 wherein the first generation hybrid is a blend 

 and segregation occurs in the second genera- 

 tion according to Mendelian formula. Whereas 

 it has been found that Shorthorn coat color is 

 neither one unit nor a single group of units, 

 but behaves in heredity as two units, or unit 

 groups, the areas for the white hairs in the 

 roan behaving as one unit, and the areas for 

 the red as another. Moreover, a red mated 

 with a red does not always produce a red, al- 

 though it generally does so. If the whole coat 

 color were a single unit, behaving in Mendel- 

 ian fashion, then red by red would produce 

 only red. To a well-known exception of this 

 sort the author should not be blind ; to him, as 

 he so clearly points out in reference to the 

 older studies and theories, it should point 

 toward future studies and discoveries, each 

 with its gold and dross. It would seem 

 more reasonable continually to urge the 

 analysis of gross somatic characteristics 

 into heritable units which, without excep- 

 tion, behave according to rule. However, a 

 rule that works nine times out of ten is a good 

 one for the practical man to follow, and to him 

 is an instrument of inestimable value, al- 

 though to the theorist the one exception is the 

 thing that commands his interest and work. 



To summarize, the book is a special plea for 

 the practical application of the Mendelian 

 principles to animal breeding, and as such, 

 the case is better established than in any other 

 practical breeder's guide with which the re- 

 viewer is acquainted. In general, it recog- 

 nizes the limitations of the present knowledge 

 of Mendelian traits in domestic animals, and 

 in a wholesome manner urges further investi- 

 gation, as well as the courageous application 

 of current theories by practical breeders. 



The author's style is literary, his English 

 clear, and his argument is easy to follow. 



H. H. Laughlin 



Eugenics Eecoed Office, 

 Cold Spring Hakbor, Long Island 



The First Principles of Evolution. By S. 

 Herbert. London, A. & 0. Black; New 

 York, The Macmillan Co. 1913. 



