ANIMAL LIFE AND EVOLUTION 339 



it does not say what characteristics, but only what proportion 

 of a whole personality, shall be inherited. Hence it is a gen- 

 eralization that has not been of much practical use to breeders. 

 Recently, however, great progress has been made in the study 

 and elucidation of the exact heredity behavior, in successive 

 generations, of specific traits in animals and plants, so that there 

 are now well established certain new generalizations, or "laws," 

 of heredity that are of immediate practical use to the breeder. 

 These new generalizations are known as the Mendelian 

 principles of heredity because some of them were first dis- 

 covered, by experimental work with plants, by Gregor Mendel, 

 an Augustinian monk of Austria. He did his work and 

 published his results in the years near 1860, but his conclu- 

 sions remained practically unknown until 1900. The Mendel- 

 ian principles cannot be expressed by any such single, simple 

 and comprehensive generalization as the Galtonian law of 

 ancestral inheritance. They do not attempt to treat of 

 the inherited personality of the individual as a whole but 

 concern themselves with the various separate characteristics 

 or traits of the individual. In heredity that follows the 

 Mendelian order and it may be that all inheritance may be 

 shown to do this there is no real or permanent blending, of 

 contrasted qualities, such as shortness and tallness, black and 

 white, rough and smooth, etc. Each of these conditions is 

 considered as an unmodifiable persistent unit character which 

 can be combined with or separated from others but cannot be 

 really blended with any. When two of these contrasted 

 characters are brought together by a cross-mating the offspring 

 of this mating may all show but one of these characters or 

 may all show an apparent blending of them. But in thenext 

 generation, obtained by mating these offspring together, or 

 with other similarly produced offspring, both of the original 

 contrasted characters will reappear and by proper selecting 

 and mating each may be made to breed pure again. If the 

 original cross-mating has been of such a kind as to bring 

 together several different pairs of contrasting characters, there 

 will be opportunity in the second and later generations to 

 pick out individuals showing new combinations of unit char- 



