Evolutionary Philosophy and the German War. 75 
fields of its habitat; but it is hardly to be supposed that the first patch 
of white hair that appeared upon the ancestral type of bear was per- 
petuated because it offered any great degree of security to its owner. 
Natural selection here loses its force, while discontinuous variations 
come into consideration. It is now known that the discontinuous type 
of variations, or mutations as they are called, is less rare than Darwin 
believed. To mutations is now attributed the larger share in the origin 
of races and species. The role played by mutations is illustrated by 
the recent experiments in the inheritance of the fruit fly, Drosophila. 
In laboratory cultures of these fruit flies there occur strains without 
eyes, other strains with vestigeal wings that can have no possible use- 
fulness, as well as numerous other strains with characters widely dif- 
ferent from those of the parent stock. If they had arisen in nature 
they would have been recognized without question as distinct sub-species 
at least, and probably as distinct species. Natural selection, as this and 
other cases that might be cited show, is not by any means all-powerful 
in producing new races and species. 
In late years the selection problem itself has been attacked from 
many angles, and a great deal of experimental work has been done 
on it. The problem resolves itself into these questions: Are organisms 
indefinitely variable, and by constant selection can we hope to develop 
a character at will, or can we carry on our selection only to a certain 
point, beyond which it is not effective? As yet no definite answer has 
been made, and controversy has divided students of inheritance into two 
schools. Both agree that positive results come from selection, but one 
school holds that a limit is soon reached, after which selection is no 
longer effective. According to these geneticists, selection results in a 
sorting of the different strains of which any organism is composed into 
the original pure lines. Thus the bristles numbers on the thorax of a 
fly may be selected for perhaps thirty generations with an increase in 
the mean, but at length continued selection causes no further rise in 
the mean of the bristles number. If further selection is to be effective 
a new mutation must occur. Without some such change in the germ 
plasm selection cannot be responsible for continued progressive develop- 
ment. 
According to the other school of biologists, germinal modifications 
are necessary before selection can bring about any real change in the 
organism, but these germinal changes are of such common occurrence 
that it is possible practically to continue development by selection in the 
direction desired. Between these two widely different viewpoints no 
decision can be reached, for sufficient experimental evidence is not at 
present available. Certainly there is not enough exact scientific data 
to justify relying solely upon natural selection, or making a fetish out 
of the conception of the struggle for existence. 
