362 BIOLOGY 



white with no mixture of gray fur; one of the other fourths will 

 be found to be pure gray races with no mixture of white, and 

 the other two-fourths will again prove to be a mixed race con- 

 taining both white and gray characters. This process may 

 then go on indefinitely. 



The further details of this law are too complicated to be fol- 

 lowed out in this place, but from the law it is possible to calcu- 

 late approximately how many of the offspring at each generation 

 will show recessive, and how many dominant characters. This 

 law has been of great value in directing breeding experiments, 

 and breeders who are trying to produce new varieties of animals 

 and plants find the law extremely useful in controlling their ex- 

 I HT iments toward definite ends. Mendel's law has thus shown that 

 the inheritance by the offspring of the characters of the parents 

 is not a pure matter of chance, but is controlled by definite 

 laws. While we do not yet fully understand these laws, the fact 

 that some of them have been discovered gives promise that we 

 may, in time, be able to control the process of inheritance far 

 more accurately than hitherto. 



It is not believed by those who have worked on Mendel's 

 law that all characteristics of organisms are thus unit charac- 

 ters and are transmitted in toto or not at all. Some characters 

 appear to blend, as for example the cross between the white 

 race and the negro, the offspring of such crossing being neither 

 white nor black but mulattoes, a mixture midway between the 

 parents. Hence the color of the human skin is probably not 

 like the white and gray color in mice, a character transmitted 

 by the law of Mendel. This law of Mendel has, however, been 

 a great contribution to science in showing that large numbers 

 of characters or organisms are unit characters, and are trans- 

 mitted according to definite laws that may be clearly formu- 

 lated. 



We may say, in concluding the general subject, that modern 

 biological science recognizes the principle that race divergence 

 has been the law of life, and that the evolution of modern types 



