146 Darwin, and ajter Darwin. 



7. Isolation may be either discriminate 

 OR indiscriminate. When discriminate, it 



HAS reference TO RESEMBLANCES BETWEEN IN- 

 DIVIDUALS CONSTITUTING THE ISOLATED COLONY 

 OR GROUP; WHEN INDISCRIMINATE, IT HAS NO 

 SUCH REFERENCE. IN THE FORMER CASE THERE 



arises homogamy, and in the latter case 

 there arises al'ogamy. 



8. Except where very large populations 

 are concerned, indiscriminate isolation 

 always tends to become increasingly discrim- 

 inate ; and, in the measure 'that it does so, 

 apogamy passes into homogamy, by virtue of 

 Independent Variability. 



9. Natural Selection is one among many 

 other forms of discriminate isolation, and 

 presents in this relation the following 

 peculiarities :—(<^) the isolation is with 

 reference to superiority of fitness ; {b) is 

 effected by death of the excluded indi- 

 viduals; and {c) unless assisted by some 

 other form of isolation, can only effect 

 monotypic as distinguished from polytypic 

 evolution. 



10. It is A GENERAL LAW OF ORGANIC EVOLUTION 

 THAT THE NUMBER OF POSSIBLE DIRECTIONS IN 

 WHICH DIVERGENCE MAY OCCUR CAN NEVER BE 

 MORE THAN EQUAL TO THE NUMBER OF CASES OF 

 EFFICIENT ISOLATION ; BUT, EXCEPTING NATURAL 

 SELECTION, ANY ONE FORM OF ISOLATION NEED 

 NOT NECESSARILY REQUIRE THE CO-OPERATION 



