178 THE POPULAR SCIENCE MONTHLY. 



necessary for the crossing of different species must constantly occur, 

 and yet the species remain distinct. The same is true of many her- 

 maphrodite species of marine animals living in great numbers togeth- 

 er ; the water is full of the sperm of several species, and the condi- 

 tions of cross-contact of sexual elements are constantly present, and 

 yet species remain substantially distinct. 



It is evident, therefore, that in close-breeding, and in the crossing 

 of varieties of different degrees of divergence, there is, first, a less than 

 average result, then an average, then better than an average, then this 

 better result quickly reaches a maximum and again declines, crosses 

 the line of average and becomes bad, and finally infinitely bad, or dies 

 out. In the human species it is probable that the crossing of those 

 varieties called national varieties, even strong national varieties, pro- 

 duces good results ; but the crossing of varieties so divergent as those 

 called primary races is probably bad — these approaching too nearly 

 the nature of different species. 



The general law of the effect of breeding may therefore be graphi- 

 cally represented by the following diagram, in which the absciss A B 

 represents the level of average result, distance on this absciss from 

 the middle point a represents the divergence of crossing varieties, and 

 ordinates positive and negative represent the result of crossing, wheth- 

 er good or bad. Further, the middle point a represents no divergence 

 or identical individuals, the distance b h individual differences, c c di- 

 vergence constituting slight varieties, d d strong varieties, // races, 

 and g g species. By inspection of the figure it is seen that close-breed- 

 ing (a) produces negative ordinates or bad results, then going from this 



point the curve crosses the line of average at h h, then the ordinates 

 become positive and reach maximum at d d, or strong varieties, then 

 again crosses the line of average and becomes negative at //, indicat- 

 ing the bad effect of crossing races, and finally becomes infinitely neg- 

 ative before it reaches g g, showing the practical infertility of crossing 

 different species under natural conditions. 



If I am right in this view, then the mixing of primary races is bad, 

 and such mixed races, as weaker varieties in the struggle for life, must 

 perish. There is one possibility which may save these races. Admit- 

 ting the fact of deterioration as an immediate result of universal cross- 

 ing of existing races, it is possible that by judicious crossing again of 

 the slight varieties which must eventually arise in the mixed race, this 



