A SKETCH OF HIS LIFE 
41 
from non-vital phenomena — to say that hfe is the sum of the 
physical properties of protoplasm is to make a dogmatic assertion, 
although to gainsay it is to make another. But with the progress 
of science this gap may be bridged over at some time. Should it 
be bridged over, and life in all of its aspects be found to be pro- 
toplasmic," still we should not know why synthesis of compounds 
results in an organism or why a vital action is the outcome of 
protoplasmic changes. In respect to organisms and vital actions 
we should still be where we are now in respect to simple gravi- 
tation phenomena, for with respect to them all that we can say 
is that the stone will fall (if the future be like the past), but 
why it should fall we do not know. 
This being the nature of our knowledge, present and future, 
what should the biologist seek to discover, and what are the 
problems that peculiarly concern him? Life is defined as a 
continuous adjustment of internal to external relations (Spencer), 
and it is pointed out that synthesized protoplasm, even were it 
capable of nutrition, growth, reproduction, and contraction, 
would not be a living thing if it were not also able to maintain 
persistent adjustment to the shifting world around it. The 
essence of the living thing and that which distinguishes it from 
other forms of matter is this very adjustment. Fitness, adaptive 
response, is therefore what we should seek to study in biology. The 
mechanism itself is of subordinate importance. Study it as we 
may, we cannot thus go far forwards, since our knowledge of nature 
never includes a perception of any necessary causal connection 
between events, such as would make it possible to discover vital 
phenomena by reasoning deductively from protoplasmic pecu- 
liarities. A corollary of practical import is that the naturalist 
should endeavor to study living things in connection with their 
environment. 
Biology being thus defined as the study of adaptive response, the 
nature and evolution of man's reason and knowledge fall within 
its scope. For these are conceivably but the outcome of adaptive 
responses in the beginning as simple as the geotropism of a seed- 
ling's radicle. The ability, for instance, to make a distinction 
between what in practical life we call a truth, a real occurrence, 
