96 Evolution and Adaptation 
A definite change in the surroundings might bring about 
a definite change in the next generation, because the new con- 
dition acts either on the developing organism, or on the egg 
itself from which the individual develops. The distinction 
may be one of importance, for, if the new condition only 
effects the developing organism directly, then, when the in- 
fluence is removed, there should be a return to the former 
condition; but if the egg itself is affected, so that it is 
fundamentally changed, then the effect might persist even if 
the animal were returned to its former environment. More 
important still is Darwin’s recognition of the cumulative 
effect in a given direction of external influences, for a new 
variation, that was slight at first, might, through prolonged 
action, continue to become more developed without any other 
processes affecting the organism. 
From the Darwinian point of view, however, the all-im- 
portant source for the origin of new forms is the fluctuating 
variation, which is made use of both in the process of arti- 
ficial and of natural selection. We may now proceed to 
inquire how this is supposed to take place. 
It has been stated that, by means of artificial selection, 
Darwin believes the breeder has produced the greater number 
of domesticated animals and plants. The most important 
question is what sort of variations he has made use of in 
order to produce his result. Has he made use of the 
fluctuating variations, or of the definite ones? It is diffi- 
cult, if not impossible, to answer this question in most 
cases, because the breeder does not always distinguish be- 
tween the two. There can be little question, however, that 
he may sometimes have made use of the definite kinds, 
whether these are the outcome of external or of internal 
influences. The question has been seriously raised only in 
recent years, and we are still uncertain how far we can accu- 
mulate and fix a variation that is of the fluctuating kind. In 
a few cases it has been found that the upper limit is soon 
