24 ESSAYS OF A BIOLOGIST 



extinguished and replaced by another type 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 not- 

 able physical specialization except the upright 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 actions 

 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 experience. 

 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 nonsense to talk 

 of a cunning crab, and, though we might properly 

 ascribe wariness to a trout, I would not like to speak 



^ See Lloyd Morgan, '20 j Washburn, '135 Kohler, '21. 



