76 Heredity and Environment 



fluctuations of organisms due to environmental changes, it hap- 

 pens that in all cases offspring differ more or less from their par- 

 ents and from one another. No two children of the same family 

 are ever exactly alike (except in the case of identical twins which 

 have come from the same oosperm.* Every living being appears 

 on careful examination to be the first and last of its identical 

 kind. This is one of the most remarkable peculiarities of living 

 things. The elements of chemistry are constant, and even the 

 compounds fall into definite categories which have constant char- 

 acteristics. But the individuals of biology are apparently never 

 twice the same. This may be due to the immense complexity of 

 living units as contrasted with chemical ones, indeed lack of 

 constancy is evidence in itself of lack of analysis into real ele- 

 ments or of lack of uniform conditions, but whatever its cause 

 the extraordinary fact remains that every living being appears to 

 be unique. "Reproduction is the generation of unique beings 

 that are, on the average, more like their kind than like anything 

 else" (Brooks). 



There seems to be no reason to doubt that all the extraordinary 

 .differences which organisms show, as well as all of their resem- 

 blances, are due to differences or resemblances in the hereditary 

 and environmental factors which have been operative in their 

 development. But in view of this universal variability of organ- 

 isms it is not surprising that inheritance has seemed capricious and 

 uncertain, "a sort of maze in which science loses itself." 

 B. STATISTICAL STUDY OF INHERITANCE 



Francis Galton was one of the first who attempted to reduce the 

 mass of conflicting observations on heredity and variation to 

 some system and to establish certain principles as a result^) f sta- 

 tistical study. He was the real founder of the scientific study of 

 inheritance ; he studied characters singly and he introduced quan- 

 titative measures. Gallon's researches, which were published 

 in several volumes, consisted chiefly in a study of certain families 



* See p. 229. 



