EVOLUTION 357 



change we have no definite knowledge. In many cases 

 it must be due to internal processes about which it is 

 hardly possible even to guess ; but the question is being 

 continually asked whether changes in the germ-plasm can 

 or cannot be induced by changes in the surroundings and 

 conditions of life of the animal within whose body the germs 

 are developed and sheltered. Here we are faced with a 

 possible factor of evolution as to which the greatest con- 

 troversy has prevailed — the influence of the environment 

 and the activities of the individual organism on the progress 

 of the race to which it belongs. There is no doubt whatever 

 that an individual insect is itself affected by what it does 

 and experiences. The course of development, both before 

 and after hatching, although it depends on the inherited 

 constitution of the embryo or larva, requires a definite and 

 suitable environment if it is to be worked out to its normal 

 close, so that the young may attain maturity and in turn 

 leave offspring to carry on the race. The question at issue, 

 however, is whether the inherited nature of succeeding 

 generations can be affected by the conditions of the nurture 

 (in a wide sense) to which individuals of the parent genera- 

 tion may be subjected. If this question be answered 

 affirmatively, it may be assumed that in a series of genera- 

 tions subject to the same influences there will be a cumulative 

 effect on the inherited characters, and as a result the possi- 

 bility of progressive change. 



The importance of this factor in evolution (it is now 

 conveniently known as the factor of " use-inheritance ") 

 was strongly advocated more than a century ago by the 

 famous French naturalist J. B. de Lamarck (1809), who 

 endeavoured to prove that the racial development of the 

 whole animal kingdom was due to " acquired changes." 

 He observed that " the environment affects the shape 

 and organisation of animals," and influences their activities 

 and habits ; and from these premises — true to some extent 

 at least — he inferred that the changes thus impressed upon 

 the individual must become part of the racial inheritance. 

 " The frequent use of any organ . . . leads to its development 



