306 GENETICS AND EUGENICS 



standards demand it, but because avoidance of loathsome 

 venereal disease is impossible otherwise. 



This element of venereal disease has frequently been an 

 important factor in determining the success or failure of race 

 mixtures. European men of loose morals have frequently 

 introduced venereal disease in race mixtures with native 

 populations, and this will account for the poor results ob- 

 served in many racial crosses. When this element is absent, 

 racial crosses of Europeans with native peoples have been 

 observed to produce offspring of complete vigor and fertility. 

 Racial crossing among men, as among domesticated animals, 

 is biologically beneficial within limits. The English people 

 were originally very mixed racially, and the same is pre- 

 eminently true of Americans today. This mixture of elements 

 not too dissimilar, provided the social heritage is not unduly 

 disturbed, is on the whole beneficial. It results in increase 

 of vigor and energy in the offspring, together with an in- 

 crease of variability, physical and mental, which favors social 

 progress. 



It is certain that human progress depends upon two sets of 

 agencies, one sociological or cultural, the other biological. 

 In this discussion we have dealt chiefiy with the biological 

 agencies. Biologically the human race can be improved only 

 by improvement of its germ-plasm. If acquired characters 

 were inherited, we might hope to improve the human race 

 germinally by improving the environment. If as seems 

 more probable acquired characters are not to any consider- 

 able extent inherited, then environmental agencies affect man 

 chiefly culturally, not biologically. To change man biologi- 

 cally, to make a different sort of animal of him, it will be 

 necessary to act through heredity, that is through selection 

 of parents for the next generation. 



Leaving aside for the present the practical difficulties arid 

 supposing that it were possible to manage the human race 

 like a stock farm, the choice of parents would necessarily 

 be limited by the material available. We could select parents 

 only for such characteristics as the human race today pos- 



