210 
KEY. J. T. GTTLICK ON D1YEHGENT EVOLUTION 
failure of the unsuccessful cannot he the cause of separation be- 
tween the different kinds of the successful, then Selection, whether 
Natural, or Reflexive, or of any other kind , cannot he the cause of 
Divergent Evolution, except as co-operating with some cause of 
Independent Generation. 
The failure of Sexual Selection, without Separation or Segrega- 
tion, 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 colour 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 cannot be the cause of diver- 
gent evolution, unless there are added to it other causes that pro- 
duce 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 disadvantages of their position their opportunities 
for gaining subsistence, and therefore for rearing families, 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 Iustitutional 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 
