462 Evolution and Adaptation 
determine, whether, if after several mutations have succes- 
sively appeared in the same direction, there would be an 
established tendency to go on in the same direction in some 
of the future mutations. But here again we must wait until 
we have more data before we attempt to build up a theory 
on such a basis. 
The attacks on the Darwinian school by the followers of 
the modern school of experimentalists are with few exceptions 
based on the assumption that the natural selectionists pre- 
tend that their principle is a sort of creative force, —a factor 
in evolution in the sense of being an active agent. This 
assumption of the selectionists has led many of them to ig- 
nore a fundamental weakness of their theory, namely, the 
origin of the variations themselves, although Darwin did 
not overlook or ignore this side of the problem, or fail to 
realize its importance, as have some of his more ardent, but 
less critical, followers. They have contented themselves, asa 
rule, with pointing out that certain structures are useful, and 
this has seemed to them sufficient proof that the structures 
must have been acquired because of their value. In contrast 
to this complacency of the selectionists, we find here and 
there naturalists who have, from time to time, insisted that 
the scientific problem of evolution is not to be found in the 
principle of selection, but in the origin of the variations 
themselves. _ It will be clear, from what has been said, that 
this is our position also, and for us adaptation itself does not 
appear to be any more a problem that can be examined by 
scientific methods, than the lack of adaptation. The causes 
of the change of whatever kind should be our immediate quest. 
The destruction of the unfit, because they can find no place 
where they can exist, does not explain the origin of the fit. 
Over and beyond the primary question of the ovigiz of the 
adaptive, or non-adaptive, structure is the fact that we find 
that the great majority of animals and plants show distinct 
evidence of being suited or adapted to live in a special envi- 
