2 o BIONOMIC LAWS. 



tli.it selection is necessary to maintain the distinctive characters of 

 the species. The effect of cessation of selection is a subject of great 

 interest, on which further light is needed. In dealing with an ordi- 

 nary species, the breeder assumes that the exclusive propagation of 

 average forms will tend to produce stability of type rather than rever- 

 sion ; and he ignores any difference that may exist between the birth- 

 average and the adult-average. His only hope of producing diver- 

 gent races is found in the separate breeding of forms that are manifest 

 departures from both the birth-average and the adult-average in 

 some given direction. If sheep with long and fine wool are desired, 

 he selects sheep possessing these qualities in the highest degree as 

 the i 'lies from which to raise his flocks. 



5. The Amalgamation of Races. 



Once more, the breeder finds that the free crossing of different 

 races introduces great variation, with the breaking down of race dis- 

 tinctions. The interfusion of races, with the strange preponderating 

 influence that belongs to some races, or sometimes to one sex of a 

 given race, is a subject that is worthy of fuller study than has yet 

 been given to it. 



6. The Influence of Acquired Cliaracters on Racial Characters. 



Fully satisfactory proof or disproof of the direct inheritance of 

 acquired characters has not yet been accumulated; but as I pointed 

 out in my paper on "Intensive Segregation," reproduced in Appendix 

 II of this volume, their indirect influence on inheritance is certain; 

 for "All diversities of environal selection that do not vary according 

 to differences in the environment must be classed as diversities of 

 active selection (or endonomic selection, as I sometimes call the prin- 

 ciple) , for they must have originated in some variation of the powers 

 of the organism, or in the diversity 0} uses to which it has put its 

 powers."* In the same paper I further called attention to the fact 

 that where a group of species possessing extremely limited powers 

 and opportunities for migration are distributed in a district, where 

 all the other species of both plants and animals have the usual 

 powers and opportunities for migration, here we find the group, with 

 limited facilities for migrating, varying, though the environment, 

 both physical and organic, is essentially the same. Observation also 

 teaches us that when a gravid female of a variable species is isolated 



* The small species of Achatinella found in the valleys in the northwestern por- 

 tion of the island of < >;ihu have different habits of feeding from those of larger size 

 found near the eastern end of the island. (See Plate II and the explanation 

 of the same. Chapter IV.) 



