SUMMARY OF EVOLUTION THEORIES. 

 SUMMARY OF EVOLUTION THEORIES. 



775 



(Axiom or Truism.) 



Changes are all ultimately due to the External Influences 

 and the Nature of the Organism, i.e. of Protoplasm. 



{Environment. ) 



Changes in the 

 environment are 

 followed by changes 



in the organism, 

 either — or (b) in 

 [a) in its its germ 



body, cells, 



or (c) in {/>) through 



[Environmental 

 Modifications. ) 



Degree of trans- 

 missibility unknown. 



Such environ- 

 mental modifications, 

 IF transmissible, and 

 if the originating con- 

 ditions persist for 

 some time, might 

 perhaps give rise to 

 new species, especi- 

 ally if favoured by 

 natural selection and 

 isolation. In the 

 individual lifetime 

 they may serve to 

 shield the incipient 

 stages of variations 

 in a similar direction. 



{Organism.) 



Constitutional, 

 congenital, or ger- 

 minal variations 

 arising from the 

 nature of proto- 

 plasm, or from the 

 changes necessarily 

 associated with fer- 

 tilisation, may be 

 continuous or dis- 

 continuous, quanti- 

 tative or qualitat- 

 ive, etc. 



( Variations.) 

 Transmissible. 



Such variations 

 probably supply the 

 usual material for 

 the origin of new 

 species, for the 

 establishment of 

 which, more or less 

 natural selection 

 (elimination) and 

 isolation must be 

 necessary, according 

 to the nature of the 

 variation. 



{Function.) 



Use and disuse of 

 parts, or change of 

 function (due to 

 change of environ- 

 ment or to ger- 

 minal change), are 

 followed by changes 

 in — {a) the body of 

 the organism, or {/>) 

 in the germ cells, 

 either directly or (?) 

 through {a). 



{Functional 

 Modifications. ) 



Degree of transmis- 

 sibility unknown. 



Such functional 

 modifications, IF 

 transmissible, and 

 if the originating 

 conditions persist 

 for some time , migh t 

 perhaps give rise to 

 new species, espe- 

 cially if favoured 

 by natural selection 

 and isolation. In 

 the individual life- 

 time they may serve 

 to shield the in- 

 cipient stages of 

 variations in a 

 similar direction. 



