24 ESSAYS OF A BIOLOGIST 



which to all outward appearance is similar, no better 

 adapted to the conditions of life. But the two types 

 differ in one point: the later possessed a larger brain, 

 and so, from all analogy, a better mind. Or, to take 

 another example, man differs from the lower animals 

 in no notable physical specialization except the up- 

 right posture. 



After this critical point in the evolution of organ- 

 isms was reached, further development has consisted 

 chiefly in the development of mind: and this has 

 meant, from the objective, purely biological stand- 

 point, the possibility of summing-up ever more and 

 more power and fine adjustment of response in the 

 present, in the single act.^ 



The first main function of the improved adjustor 

 mechanism was to make ever more complicated ac- 

 tions possible; but this again tended speedily to a 

 limit. The next step was to make it possible for the 

 past to act in the present. Through associative 

 memory, present behaviour is modified by past ex- 

 perience. What this has meant to organisms can be 

 realized if we reflect that certain terms which can 

 justly be applied to a mammal or a bird have no real 

 meaning if applied to lower forms. If we speak 

 of a cunning wolf or a wary crow, we imply that their 

 life has taught them new qualities; but it is non- 

 sense to talk of a cunning crab, and, though we 

 might properly ascribe wariness to a trout, I would 

 not like to speak of a wary Amoeba. In the same 



«See Lloyd Morgan, '20; Washburn, '13; Kohler, '21. 



