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 hypothesis 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 geological evidence and
embryological research, that in the history both of races and of
individuals the various mechanisms in question have themselves had a
history--beginning in the forms of most uniformity and simplicity,
gradually advancing to forms more varied and complex, nowhere exhibiting
any interruptions in their upward progress, until the world of organic
machinery as we now have it is seen to have been but the last phase of a
long and gradual growth, the ultimate roots of which are to be found in
the soil of undifferentiated protoplasm.

[36] It is often objected to Darwin's terminology, that it embraces
such words as "contrivance," "purpose," &c., which are strictly
applicable only to the processes or the products of thought. But
when it is understood that they are used in a neutral or
metaphorical sense, I cannot see that any harm arises from their
use.

Lastly, when there is supplied to us the suggestion of natural selection
as a cause presumably adequate to account for this continuous growth in
the number, the intricacy, and the perfection of such mechanisms, it is
only the most unphilosophical mind that can refuse to pause as between
the older hypothesis of design and the newer hypot