NATURAL SELECTION 51 
The fact that organic beings on the whole are, as a 
general rule, very closely fitted for the conditions in 
which they have to pass their lives is clearly shown 
by the study of adaptations. This is a subject which 
those followers of Darwin who believe in the all- 
sufficiency of natural selection have brought into con- 
siderable prominence. For a full account of many 
supposed beautiful adaptations, from the point of view 
of the most prominent member of the school in ques- 
tion, reference may be made to Weismann’s recently 
published book, ‘ The Evolution Theory.’ 
On the theory of natural selection in its extreme 
form, all the parts of an animal or plant—or, at any rate, 
all the points in which one species differs from another 
nearly related species—are supposed to have arisen on 
account of their usefulness to the creatures possessing 
them. Every detail of structure is thus regarded as 
being more or less closely adapted to the circum- 
stances which attend the life of the animal or plant in 
question. This adaptation is never, indeed, regarded 
as perfect, because natural selection is always in 
progress, and its work is never absolutely done; 
but the point is that the features of every part are 
aimed at some useful purpose; or, if they are not, 
then they have been useful in former times and under 
different circumstances, and are now undergoing a 
process of gradual] removal, because the individuals in 
which the useless structure is least developed will now 
have the best chance of surviving. That the form and 
structure of an animal or plant is in general closely 
fitted to its environment is of course true ; otherwise 
4—2 
