Biology | Page 4

of which it is our
tremendous task to determine to such extent as we may be able. But
this does not yet touch the most essential side of the problem. What is
most significant is that the clumsy, short-necked elephant has been
endowed--"by nature," as we say--with precisely such an organ, the
trunk, as he needs to compensate for his lack of flexibility and agility in
other respects. If we are asked why the elephant has a trunk, we must
answer because the animal needs it. But does such a reply in itself
explain the fact? Evidently not. The question which science 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 of its construction is a structural
adaptation; and when such adaptations are given the mechanist has for
the most part a relatively easy task in his interpretation. He has a far
more difficult knot to disentangle in the case of the so-called functional
adaptations, where the organism modifies its activities (and often also
its structure) in response to changed conditions. The nature of these
phenomena may be illustrated by a few examples so chosen as to form
a progressive series. If a spot on the skin be rubbed for some time the
first result is a direct and obviously mechanical one; the skin is worn
away. But if the rubbing be continued long enough, and is not too
severe, an indirect effect is produced that is precisely the opposite of
the initial direct one; the skin is replaced, becomes thicker than before,
and a callus is produced that protects the spot from further injury. The
healing of a wound involves a similar action. Again, remove one
kidney or one lung and the remaining one will in time enlarge to
assume, as far as it is able, the functions of both. If the leg of a
salamander or a lobster be amputated, the wound not only heals but a
new leg is regenerated in place of that which has been lost. If a
flatworm be cut in two, the front piece grows out a new tail, the hind
piece a new head, and two perfect worms result. Finally, it has been
found in certain cases, including animals as highly organized as
salamanders, that if the egg be separated into two parts at an early
period of development each part develops into a perfect embryo animal
of