256 ESSAYS OF A BIOLOGIST 



But finally a kink occurs, a critical point similar 

 to that seen at the origin of living from non-living 

 matter. There the attributes of living matter which 

 mark it off from inorganic matter become dominant 

 — its capacity for self-reproduction, its tendency to 

 organization. The colloid carbon compound had 

 been the highest known independent unit; from now 

 on this place was taken by the organism. 



In exactly the same way, in the final stages of evo- 

 lution (as witnessed abundantly by fossil mammals) 

 complexity of purely bodily organization had reached 

 a limit, and survival, as is evidenced by increasing 

 size of brain, came to be determined more and more 

 by mental qualities. Finally the curve of mental 

 development caught up with that of body, and inter- 

 sected it: mind became the dominant factor in the 

 new type of organism, and in the subsequent his- 

 tory of the evolutionary process. The organism 

 ceased to be the highest unit, and gave place to the 

 person, or self-conscious individual with organized 

 mind. 



This new critical point was reached when man 

 arose; many authors recognize it for what it is, the 

 beginning of a new era, by christening the subse- 

 quent geological period the Psychozoic. That pe- 

 riod, geologically speaking, has not yet run but a tiny 

 span; and we are no more entitled to think that 

 we have reached or even imagined the possibilities of 

 its future evolution than we should have been en- 

 titled to regard the possibilities of purely biological 



