cience must seek to answer, is _how_ came the elephant to have a
trunk; and we do not properly answer it by saying that it has
developed in the course of evolution. It has been well said that even
the most complete knowledge of the genealogy of plants and animals
would give us no more than an ancestral portrait-gallery. We must
determine the causes and conditions that have cooperated to produce
this particular result if our answer is to constitute a true
scientific explanation. And evidently he who adopts the machine-theory
as a general interpretation of vital phenomena must make clear to us
how the machine was built before we can admit the validity of his
theory, even in a single case. Our apparently simple question as to
why the animal has a stomach has thus revealed to us the full
magnitude of the task with which the mechanist is confronted; and it
has brought us to that part of our problem that is concerned with the
nature and origin of organic adaptations. Without tarrying to attempt
a definition of adaptation I will only emphasize the fact that many of
the great naturalists, from Aristotle onward, have recognized the
purposeful or design-like quality of vital phenomena as their most
essential and fundamental characteristic. Herbert Spencer defined life
as the continuous _adjustment_ of internal relations to external
relations. It is one of the best that has been given, though I am not
sure that Professor Brooks has not improved upon it when he says that
life is "response to the order of nature." This seems a long way from
the definition of Verworn, heretofore cited, as the "metabolism of
proteids." To this Brooks opposes the telling epigram: "The essence of
life is not protoplasm but purpose."

Without attempting adequately to illustrate the nature of organic
adaptations, I will direct your attention to what seems to me one of
their most striking features regarded from the mechanistic position.
This is the fact that adaptations so often run counter to direct or
obvious mechanical conditions. Nature is crammed with devices to
protect and maintain the organism against the stress of the
environment. Some of these are given in the obvious structure of the
organism, such as the tendrils by means of which the climbing plant
sustains itself against the action of gravity or the winds, the
protective shell of the snail, the protective colors and shapes of
animals, and the like. Any structural feature that is useful because