286 DIVERGENT EVOLUTION THROUGH SEGREGATION. 
difference in their tastes to the fact that, when there was but one group 
and the tastes of all were conformed to a single standard, some of the 
competitors failed of propagating, through being crowded aside by 
those more successful? If the failure of the unsuccessful can not be the 
cause of separation between the different kinds of the suceessful, then selec- 
tion, whether natural or reflexive, or of any other kind, can not be the cause 
of divergent evolution, except as co-operating with some cause of independ- 
ent generation. 
The failure of sexual selection, without separation or segregation, to 
account for divergent evolution, will perhaps be made clearer to some 
minds by considering some of the particular conditions under which it 
occurs. Suppose for instance that in some species of humming bird 
there occurs a slight variation in the form or color of the tail feathers 
of the male that adds to the beauty of the individuals possessing the 
new character and rendering them more attractive to the females. We 
can see that they might have an advantage over their rivals in leaving 
progeny, and that the variety might in that way gradually gain the 
ascendency, and the beauty of the markings become more and more 
completely defined; but under such conditions what could prevent the 
whole species from being gradually transformed? Unless there was 
some separative or segregative principle that prevented the new variety 
from crossing with the others, the species would remain but one, though 
changed in some of its characters. We should have transformation 
without divergence. 
The same must be true of institutional selection. It may be the 
cause of transformation; but it can not be the cause of divergent evolu- 
tion, unless there are added to it other causes that produce divergence 
in the character of the forms selected, and the separate breeding of the 
different groups of forms thus selected. <A single illustration will set 
in a clear light the limitation in the influence of institutional as well 
as all other selection. In primitive communities the deaf are but little 
cared for, and owing to the great disadvantage of their position their 
opportunities for gaining subsistence, and therefore for rearing fami- 
lies, are greatly diminished; this is natural selection. Again, those 
who are at so great a disadvantage in communicating with their com- 
panions will be also at a disadvantage in finding consorts; this we may 
call social selection. Again,a community might either by law or by 
strict custom prevent the marriage of the deaf; this would be institu- 
tional selection. Any one of these forms of selection might be pressed 
so far as to be the means of increasing the average power of hearing in 
the community in succeeding generations; but it could never be the 
cause of two divergent races, one with good powers of hearing and the 
other with an increasing liability to deafness. To secure such diver- 
gence it is necessary that segregative influences should be introduced, 
such as have been most amply furnished by the modern system of edu- 
cation for the deaf. Under these influences those endowed with hear- 
