1896.] A New Factor in Evolution. 443 



Assuming that there are such new or modified functions, in 

 the first instance, and such " acquired characters," arising by 

 the law of " use and disuse " from these new functions, our far- 

 ther question is about them. And the question is this : How 

 does an organism come to be modified during its life history? 



In answer to this question we find that there are three dif- 

 ferent sorts of ontogenic agencies which should be distin- 

 guished — each of which works to produce ontogenetic modifi- 

 cations, adaptations, or variations. These are : first, the physi- 

 cal agencies and influences in the environment which work 

 upon the organism to produce modifications of its form and 

 functions. They include all chemical agents, strains, con- 

 tacts, hindrances to growth, temperature changes, etc. As far 

 as these forces work changes in the organism, the changes 

 may be considered largely " fortuitous " or accidental. Con- 

 sidering the forces which produce them I propose to call them 

 " physico-genetic." Spencer's theory of ontogenetic develop- 

 ment rests largely upon the occurrence of lucky movements 

 brought out by such accidental influences. Second, there is a 

 class of modifications which arise from the spontaneous activ- 

 ities of the organism itself in the carrying out of its normal 

 congenital functions. These variations and adaptations are 

 seen in a remarkable way in plants, in unicellular creatures, 

 in very young children. There seems to be a readiness and 

 capacity on the part of the organism to "rise to the occasion," 

 as it were, and make gain out of the circumstances of its life. 

 The facts have been put in evidence (for plants) by Henslow, 

 PfefFer, Sachs; (for micro-organisms) by Binet, Bunge; (in 

 human pathology) by Bernheim, Janet ; (in children) by 

 Baldwin (ref. 2, chap, vi.) (See citations in ref. 2, chap, ix, and 

 in Orr, Theory of Development, chap. iv). These changes I pro- 

 pose to call " neuro-genetic," laying emphasis on what is called 

 by Romanes, Morgan and others, the " selective property " of the 

 nervous system, and of life generally. Third, there is the 

 great series of adaptations secured by conscious agency, which 

 we may throw together as " psycho-genetic." The processes 

 involved here are all classed broadly under the term "in- 

 telligent," i. e , imitation, gregarious influences, maternal in- 



