The Theory of Evolution 231 
as we have supposed, external conditions may sometimes cause 
adaptive changes in adult organisms, i.e. in their body-cells, 
and if the egg is at times similarly affected so that the next genera- 
tion shows from birth the same changes; and further if these 
general changes are mutations, i.e. fixed in character, it will 
appear as though the process of adaptation and of evolution has 
taken place at the same time. It appears, however, when the 
whole field of variation is examined that this is only a special 
case. In other cases the changes affected by external conditions 
may be different from those brought about in the germ-cells, 
and some of the new mutations may be adapted to a different 
environment, or to the old one in a different way. In both cases 
the problem is fundamentally the same, and it is the process of 
variation that is our real problem. 
Lloyd Morgan, Osborn, and Baldwin have suggested that adult 
animals may at times become adapted to a new environment 
by a direct response, as by the use and disuse of certain organs 
of the body, and maintain themselves in this way until the proper 
germinal variations occur that fix, as it were, the new characters 
so that they become a part of the permanent inheritance of the 
species. Thus the organism, owing to its power of responsive 
adaptation, adjusts itself to a suitable environment and awaits 
the time when the fixation of the new characters may success- 
fully be accomplished as the result of a germinal variation of 
the right sort. It is assumed that fluctuating variations bring 
about the permanent change, but obviously a mutation would 
give the same result. To what extent the advent of the new 
variation, whatever its origin, is anticipated in the way assumed, 
is not known. On the mutation theory it is doubtful whether 
this subsidiary assumption is needed to explain how new species 
arise. On the theory of the selection of fluctuating variations 
the assumption of “organic adaptation” seems to cover an ad- 
mitted weakness of Darwin’s theory, but whether the selection of 
fluctuating variations could ever fix permanently a character is 
a question that seems from the experimental evidence to be 
answered in the negative. 
