Summary and General Conclusions 463 
ronment, z.¢. their structure and their responses are such that 
they can live and leave descendants behind them. I can see 
but two ways in which to account for this condition, either 
(1) teleologically, by assuming that only adaptive, variations 
arise, or (2) by the survival of only those mutations that are 
sufficiently adapted to get a foothold. Against the former 
view is to be urged that the evidence shows quite clearly 
that variations (mutations) arise that are not adaptive. On 
the latter view the dual nature of the problem that we have 
to deal with becomes evident, for we assume that, while the 
origin of the adaptive structures must be due to purely 
physical principles in the widest sense, yet whether an organ- 
ism that arises in this way shall persist depends on whether 
it can find a suitable environment. This latter is in one 
sense selection, although the word has come to have a differ- 
ent significance, and, therefore, I prefer to use the term 
survival of species. 
The origin of a new form and its survival after it has 
appeared have been often confused by the Darwinian school 
and have given the critics of this school a fair chance for ridi- 
culing the selection theory. The Darwinian school has sup- 
posed that it could explain the origin of adaptations on the 
basis of their usefulness. In this it seems to me they are 
wrong. Their opponents, on the other hand, have, I believe, 
gone too far when they state that the present condition of 
animals and plants can be explained without. applying the 
test of survival, or in a broad sense the principle of selection 
amongst species. 
It will be clear, therefore, in spite of the criticism that I 
have not hesitated to apply to many of the phases of the selec- 
tion theory, especially in relation to the selection of the indi- 
viduals of a species, that I am not unappreciative of the great 
value of that part of Darwin’s idea which claims that the con- 
dition of the organic world, as we find it, cannot be accounted 
for entirely without applying the principle of selection in one 
