420 The Inward Urge to Change 



from simpler matter. And so, with each aggregation of 

 Hving stuff new properties and relationships emerged, mak- 

 ing possible still more complex emergences later. 



We do not know anything of the nature of the " gene " 

 or determining factor in the chromosome. We know only 

 that each such hypothetical factor does in fact influence the 

 development of various structures in the organism; and we 

 know that some body characters manifest themselves only 

 as two or more such factors are present. We may therefore 

 conceive the character as developed to be an emergence 

 from the interaction of the two or more factors. We have 

 seen that novelties sometimes arise in plants and animals 

 through the coming together of different factors from the 

 two ancestral lines. We may go farther and assume that 

 a mutation may arise as a result of the modification of one 

 or more factors. It is not then to be supposed that a new 

 character is necessarily the direct result of a modification 

 of a factor. It may be that a new character emerges from 

 the new interaction, from the adventitious coming together 

 of two or more factors that were never before present 

 together. 



The factorial hypothesis does not tell us anything about 

 the nature, structure or source of the factors. It assumes that 

 from the coming together of a and b there emerges some- 

 how a result that is different from a mere summation of the 

 doings of a and b. 



Whether the large brain of primitive man arose as a 

 single mutation, or whether it is an indication of orthogenetic 

 tendencies, it may not be necessary to find as " missing links " 

 a complete series of intergrading forms with *' hardly per- 

 ceptible differences " separating them. It should be sufficient 

 to find indications or relics of types from which primitive 

 man could conceivably have emerged. Indeed, it has been 

 seriously suggested that the overgrowth of the forebrain in 

 man, with all the consequences which that has entailed, is 

 analogous to the overgrowth of horns, teeth and plates in 

 now extinct forms; and that it may become the cause of the 



