The Theory of Natural Selection. 281 
arrangements, which might reasonably be supposed 
due, like the phenomena of crystallization, to com- 
paratively simple physical causes. On the contrary, 
they everywhere and habitually exhibit so deep-laid, 
so intricate, and often so remote an adaptation of 
means to ends, that no machinery of human contrivance 
can properly be said to equal their perfection from a 
mechanical point of view. Therefore, without question, 
the hypothesis which first of all they suggest—or 
suggest most readily—is the hypothesis of design. 
And this hypothesis becomes virtually the only hypo- 
thesis possible, if it be assumed—as it generally was 
assumed by natural theologians of the past,—that all 
species of plants and animals were introduced into 
the world suddenly. For it is quite inconceivable that 
any known cause, other than intelligent design, could 
be competent to turn out instantaneously any one of 
these intricate pieces of machinery, already adapted 
to the performance of its special function. But, on the 
other hand, if there is any evidence to show that one 
species becomes slowly transformed into another— 
or that one set of adaptations becomes slowly changed 
into another set as changing circumstances require,— 
then it becomes quite possible to imagine that a 
strictly natural causation may have had something 
to do with the matter. And this suggestion becomes 
greatly more probable when we discover, from geo- 
logical evidence and embryological research, that in 
the history both of races and of individuals the 
words as “contrivance,” ‘‘ purpose,” &c., which are strictly applicable 
only to the processes or the products of thought. But when it is under- 
stood that they are used in a neutral or metaphorical sense, I cannot see 
that any harm arises fiom their use. 
