20 BIONOMIC LAWS. 
that 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 ones 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 Characters 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 of uses to which it has put ats 
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 Oahu 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.) 
