430 THE STUDY OF ANIMAL LIFE CHAP, xxi 



tioii what determines the female's preference for one 

 suitor out of many is more probably an irresistible tout- 

 ensemble of gifts and graces and not excellence in one 

 particular decoration or quality, so in natural selection 

 it may be that what gives survival value is often a 

 general stability of constitution and efficiency of be- 

 haviour. (4) In so far as selection is in terms of a 

 previously established systematisation of inter-relations 

 -the web of life there will be a reduction of fortuitous- 

 ness and capriciousness. Natural selection is largely 

 automatic in its working, but in so far as the eliminating 

 sieve is an external system of adaptations, the sifting will 

 differ from " a chapter of accidents." Moreover, the 

 sifting process rises beyond the automatic whenever the 

 living creature takes a share in its own evolution, as it 

 often does, by selecting, changing, or even making its 

 own environment, or by active endeavours after well- 

 being, experiments with Fate, and traffickings with Time. 

 " I do not doubt," said Darwin, 'that isolation is of 

 considerable importance in the formation of new species," 

 and many evolutionists Wagner, Weismann, Gulick, 

 Romanes, Jordan, and others have worked at the idea 

 of Isolation as a directive factor in evolution. The term 

 is applied to all the means which restrict the range of 

 intercrossing within a species, whether the barriers are 

 spatial, or temporal, or habitudinal, or physiological, or 

 psychical. It is probable that isolation favours the origin 

 of distinct species by preventing intercrossing and still 

 more by bringing about close in-breeding. 



