82 Heredity and Environment 



The observational and statistical study of inheritance helped 

 to outline the problem but did little to solve it. Certain phenom- 

 ena of hereditary resemblances between ascendants and descen- 

 dants were made intelligible, but there were many peculiar and 

 apparently irregular or lawless phenomena which could not be 

 predicted before they occurred nor explained afterward. For 

 example when Darwin crossed different breeds of domestic 

 pigeons, no one of which had a trace of blue in its plumage, he 

 sometimes obtained offspring with more or less of the blue color 

 and markings of the wild rock pigeon from which domestic 

 pigeons are presumably descended. He described many cases 

 of dogs, cattle and swine, as well as many cultivated plants, in 

 which offspring resembled distant ancestors and differed from 

 nearer ones ; such cases had long been known and were spoken 

 of as "reversions." He observed many cases in which certain 

 characters of one parent prevailed over corresponding characters 

 of the other parent in the offspring, this being known as "pre- 

 potency"; but there was no satisfactory explanation of these 

 curious phenomena. They did not come under either of Galton's 

 "laws," and their occurrence was apparently so irregular that 

 every such case seemed to be a law unto itself. 



C. EXPERIMENTAL STUDY OF INHERITANCE 



I. MENDELISM 



The year 1900 marks the beginning of a new era in the study 

 of inheritance. In the spring of that year three botanists, 

 deVries, Correns, and Tschermak, discovered independently an 

 important principle of heredity and at the same time brought to 

 light a long neglected and forgotten work on "Experiments in 

 Plant Hybridization" by Gregor Mendel, in which this same 

 principle was set forth in detail. This principle is now generally 

 known as "Mendel's Law." Mendel, who was a monk, and later 

 abbot, 0* the Konigskloster, an Augustinian monastery in Briinn, 

 Moravia, published the results of his experiments on hybridization 



