THE CANNIBAL IN EVOLUTION 177 



least be something. Yet Keith himself says : " Can we 

 conceive that, in the stretch of time between the end of 

 the Pliocene and the middle of the Pleistocene, even allow- 

 ing two or three hundred thousand years for that space, 

 the brain of Pithecanthropus could have evolved into the 

 modern human form ? I cannot conceive such a rapid 

 rate of evolution." While by no means of the opinion that 

 Pithecanthropus was a human ancestor, for it appears 

 far more likely that he was a collateral survival if pro- 

 perly dated, it seems to me that by the operation of the 

 combined factors suggested such a rapid change might, 

 and indeed must, have taken place. If there is one thing 

 more sure than another, it is that stability of type 

 indicates a more or less stable environment. From the 

 historic view changes may be rapid, while from the physio- 

 logical and anthropological standpoint they seem too 

 negligible to be considered moulding influences. That 

 very ancient types still survive is not really a relevant 

 argument against a rapid critical period of change, unless 

 we can show that such a static condition has continued 

 through immense physical changes of the environment. 

 The partially obsolete Darwinian view of a slow aggregation 

 of minute advantageous spontaneous variations seems still 

 partly responsible for the opinion that change must neces- 

 sarily be slow. But in many states of matter they are often 

 rapid, and it cannot be shown definitely that evolution is 

 steady and continuous. Like the colloids of protoplasm, 

 on which all life finally depends, it seems to have critical 

 periods. Colloidal substances are easily influenced by 

 obscure stimuli. The origin of life as a sudden rise in the 

 organization of matter may have depended on a partic- 

 ular instance of ionization or the powerful influence of a 

 rare accidental catalyst. Planck's very theory of Quanta 



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