ZOOLOGY - BOTANr

LIBRARY

COLUMBIA UNIVERSITY
 

1
 

EVOLUTION   AND   ADAPTATION
CHAPTER   I

THE PROBLEM  OF ADAPTATION

Between an organism and its environment there takes
place a constant interchange of energy and of material. This
is, in general, also true for all bodies whether living or lifeless ;
but in the living organism this relation is a peculiar one; first,
because the plant or the animal is so constructed that it is
suited to a particular set of physical conditions, and, second,
because it may so respond to a change in the outer world
that it further adjusts itself to changing conditions, ie. the f
response may be of such a kind that it better insures the
existence of the individual, or of the race. The two ideas
contained in the foregoing statement cover, in a general way,
what we mean by the adaptation of living things. The fol¬
lowing examples will serve to illustrate some of the very
diverse phenomena that are generally included under this
head.

Structural Adaptations

The most striking cases of adaptations are those in which
a special, in the sense of an unusual, relation exists between
the individual and its surroundings. For example, the fore¬
leg of the mole is admirably suited for digging underground.
A similar modification is found in an entirely different group
of the animal kingdom, namely, in the mole-cricket, in which
the first legs are also well suited for digging. By their use the
mole-cricket makes a burrow near the surface of the ground,