64 EVOLUTION OF LIVING ORGANISMS. 



organisation which responds in the right way, and that 

 which does not. If one may be allowed to speak meta- 

 phorically, the problem before the organism is to acquire 

 such an organisation that under given conditions it will 

 react in the right way. Therefore, those individuals 

 which vary in their hereditary organisation in the right 

 direction necessarily have a better chance of succeeding. 

 Success in the struggle is the only criterion of " right " 

 and "wrong" in variation. The action of selection, it 

 must be remembered, on the hereditary factors is in- 

 direct, since it only acts on the combined product of 

 these and the environment (see p. 38) on the characters 

 of the organism as presented to it. It is these characters 

 and their variations which pass through the sieve. The 

 scope of the selection is limited to the variations pre- 

 sented ; its direction is determined by the environment. 

 This direction will always necessarily be towards better 

 adaptation ; adaptation is the keynote to evolution. If 

 the right kind of variation does not occur the organism 

 runs the risk of death, and will inevitably be exterminated 

 if the struggle is severe enough. 



When the history of Biological Science in the last fifty 

 years comes to be written, we fancy that the impartial 

 historian will not dwell with much pride on the account 

 of the criticisms of Darwinian doctrines. The violent 

 attacks of theologians, based for the most part on ignor- 

 ance and prejudice, may be forgiven and forgotten ; but 

 many of the criticisms from the pens of the biologists 

 themselves are scarcely better founded. It is often said 

 that of late years Darwinism has lost ground, and that 

 natural selection can no longer be regarded as a satisfying 

 explanation of, or even as an important factor in, the 

 process of evolution. Doubtless there is some truth in 

 the saying, at all events in so far as it appears that the 

 doctrine is not what some misguided enthusiasts may 

 have represented it to be, that it does not explain every- 

 thing, that many problems remain unsolved. Yet the 



