A SKETCH OF HIS LIFE 41 



from non-vital phenomena to say that life 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, 



