INSUFFICIENCY OF NATURAL SELECTION 403 



roots have disappeared almost completely and no chlorophyll is pro- 

 duced, but special nutritive organs, the sucker-like haustoria, are 

 developed on the slender, twining stems, and serve to extract the 

 necessary food from the host plant. The flowers, however, upon 

 which the perpetuation of the race depends, still remain in a 

 well developed condition. 



Both Sacculina and the dodder have lost the power of inde- 

 pendent existence, and if, for any reason, they were to find 

 themselves suddenly confined to an environment where there were 

 no suitable hosts, their races would inevitably become extinct. 

 (Naturejwould treat them just as she is treating the wingless 

 birds, and make them pay the penalty for the degeneration which 

 they have undergone. 



* It has sometimes been pointed out as an objection to the theory 

 of natural selection that it cannot account for the first origin of 

 favourable variations. The theory takes variations for granted 

 and assumes that some will be favourable and some not, that the 

 former will be fostered and accumulated from generation to 

 generation and the latter ruthlessly eliminated. It is further 

 alleged that variations are usually so slight at their first appear- 

 ance that they can have no selective value, and that something 

 is wanted to account for the increase of such variations along 

 apparently definite lines of utility. The theory also takes the 

 inheritance of variations for granted, and many people, as we 

 have seen, consider nowadays that this is not altogether a 

 justifiable proceeding, that while some variations undoubtedly 

 are inherited, others, and amongst them many which would be 

 likely to be of the greatest value to the organism, are not. 



We have, then, to go much deeper than the idea of natural 

 selection before we can reach a satisfactory working hypothesis 

 as to the manner in which organic evolution has taken place. 

 The problems of variation and heredity have already been dealt 

 with in earlier chapters, and it will be unnecessary to discuss the 

 matter now at great length, but there are certain points which 

 we must recapitulate in this connection. 



We have seen that somatogenic or bodily variations in the 



; individual are undoubtedly brought about by the direct action of 



I the environment and by the use and disuse of organs. We have 



1 also seen that blastogenic variations, which originate in the germ 



plasm, may likewise be brought about by the action of the 



D D 2 



