524 EVOLUTION, HEREDITY, EUGENICS 



References 



CoNKLiN, E. G. Heredity and Environment. Princeton Univ. Press. 



Metcalf, M. M. 1911. Organic Evolution. Macmillan Co. 



Morgan, T. H. 1916. A Critique of the Theory of Evolution. Prince- 

 ton Univ. Press, 



Newman, H. H. 1925. Evolution, Genetics and Eugenics. Univ. of 

 Chicago Press. 



Walter, H. E. 1930. Genetics. Revised edition. Macmillan Co. 



De lories' ''Mutations-Theories— In 1901, Hugo De Vries 

 (1848- ) of Holland announced that his studies of inheritance in 

 the evening primrose, Oenothera Lamarckiana, had led him to con- 

 clude that new species arose suddenly by what he called mutation. 

 These mutants or "sports" explained the origin of a new species in 

 nature. Some mutants were retrogressive and others progressive. 

 Later work by R. R. Gates showed that from the cytological basis 

 the new types came about through analysis of the chromatin. The 

 appearance of a new type was to be explained by a change in the 

 chromatin. 



Some of the workers with the fruit fly, Drosophila, once sug- 

 gested that the so-called mutants of De Vries are the emergence of 

 factors recessive in the ancestral stock and brought out by the 

 favorable cross. The production of mutations by high temperature, 

 x-rays, and other physical agents (see page 540) will give new 

 impetus to cytological correlations. 



Examples of mutation include the celebrated Ancon sheep, 

 which was short legged, many instances of taillessness and horn- 

 lessness in cattle, and supernumerary or reduced numbers of digits 

 in various animals. 



If we can eventually control the appearance or disappearance of 

 factors in the germplasm, we will produce an experimental evolution. 

 If not, we must confine ourselves to selection and to those influences 

 of environment that tend to bring out the qualities desired. 



The Origin of New Species According to Lamarck, C. Darwin, 

 A. Weismann, Mendel, and De Vries 12 



Lamarck. — New species result from variations induced by use and 

 disuse. Variations are inherited directly or improved in succeeding 

 generations. 



12 Modified from Locy, Biology and Its Makers. 



