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EEV. J. T. GTJLICK Olf DIVERGENT EVOLUTION 



failure of the unsuccessful cannot he the cause of separation he- 

 tiveen 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 ivith 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 Institutional 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 



