VOL. XVI. (1) ORGANIC SELECTION 67 
wide differences in acquired performance dependent partly 
upon their opportunities, and partly upon the use they 
had made of these opportunities. Such differences fall 
under the category of what are technically termed mzodz/ica- 
tions. But here comes in the point upon which everyone 
is not agreed. Some say that the modifications implied in 
the existence of differences in acquired performance are 
inherited, and contribute to the differences in natural 
ability in the offspring. They contribute, it is said, to the 
variations of natural ability. Others contend that this 
is not so. They urge that there is no sufficient evidence 
that acquired modifications of bodily structure and 
functioning, in brain, nerves, muscles, and so forth, in 
any way affect, for better or worse, the germinal cells, 
which are alone concerned in hereditary transmission. 
The Lamarckian School, which holds the former view, say 
that the acquired performance of the parents raises the 
level of natural ability in the offspring. The Weismannian 
school, which holds the latter view, say that natural ability 
in the child is not directly influenced by any modifications 
of brain or muscle tissue or functioning acquired by the 
parents. 
I cannot here discuss the gvos and cons of this difficult 
question, the main gist of which I have sketched in 
outline. I shall proceed on the assumption that Weismann 
and his followers are right, and that modifications have no 
direct influence upon the problems of heredity. And 
I shall briefly indicate the nature of a suggestion that has 
been put forward, which is to this effect—that the existence 
of modifications may have an indirect influence which may 
serve to foster variations of an adaptive type. 
Before doing so, however, it may be well to devote 
a parenthesis to the bearing of the Weismannian thesis 
upon certain questions of wide social importance. There 
can be no doubt that, in our slums and congested city 
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