DEPARTMENT OF EXPERIMENTAL EVOLUTION. 141 



age of onset of the propositus 35.5 years, parent 38.8, grandparents 

 36.9. In this series we can see no evidence of anticipation. 



(6) Pellagra. — At the request of the Thompson-Fadden Pellagra 

 Commission of New York, the Director of this Department undertook 

 a critical examination of a large number of fragmentary family his- 

 tories collected by the commission with the assistance of a trained field 

 worker from the Eugenics Record Office. Since Lombroso declared 

 that the diathesis of pellagra is hereditary, the attempt to find what 

 factors were present, if any, seemed worth while. The evidence 

 seemed to justify the conclusion that, whatever the immediate cause 

 of pellagra, the course that it followed, the particular symptons that 

 it showed, had a clear hereditary basis. Thus, in certain families 

 mental symptoms were pronounced, in others absent; in some families 

 the intestinal derangements were most striking, in others they were 

 hardly present. While the skin usually shows areas of extreme inflam- 

 mation in some families, the dermal symptoms were hardly to be 

 noticed in others. The characteristic differences in families affords the 

 best evidence of certain constitutional hereditary differences — which 

 determine or control the specific symptoms of pellagra. 



(7) Osteopsathyrosis. — A study was made of all available pedigrees 

 of hereditary brittleness of bones. The conclusion is drawn that the 

 trouble is indeed hereditary and that the factor which determines the 

 imperfect, brittle development of long bones is a dominant one. This 

 conclusion is based on the fact that, as Griffith pointed out some years 

 ago, the inheritance is generally direct, i. e., does not skip a generation, 

 but appears in one parent and one of that parent's parents. Further 

 evidence that the trait depends on a single dominant factor is found 

 in the proportions of the fraternity who are affected. Out of a total 

 of 150 offspring of an affected parent 83 or 55 per cent are affected — not 

 far from the 50 per cent that was to be expected on hypothesis. The 

 phenomena associated with fragility of bones are not always alike 

 in different families. In some families the bones are broken before 

 birth; in others only after the infant has grown into a child. Families 

 differ in the degree of pressure necessary to breakage and in the bone 

 most apt to be broken. The '^ classical symptoms" of osteopsathyrosis 

 constitute a syndrome whose elements are separately inheritable. 



(8) Stature. — An analysis of the inheritance of the elements of 

 human stature has been undertaken. Several hundred pedigrees of 

 total stature have been analyzed, but more extensive data of another 

 kind are being collected and analyzed. 



THE PROCESSES OF FORMING SPECIES IN NATURE AND ARTIFICIALLY. 

 BUILDING UP A RACE BY SELECTION OF FAVORABLE MUTANTS. 



Since the general acceptance of the mutation theory and its corollary, 

 that of absence of evolution through the selection of non-inheritable 

 fluctuations, it has become important to test the application of these 

 principles in the production of new species. Dr. Harris has for the 



