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the developmental variation arose in the female in response to 

 changes of environment ; while if both sexes were exposed to the 

 same changes of environment necessitating the same functional 

 modifications to be acquired to bring them into better adaptation 

 with their surroundings, it is reasonable to conclude that the result 

 would be the production of a greater difference in a shorter space 

 of time. 



"Thus it is clear that the gradual accumulation of slight devel- 

 opmental variations transmitted in accordance with the law of ear- 

 lier inheritance would be sufficient to cause the origin of various 

 species ; and at the same 1 time there can be little doubt that this 

 cause has also been assisted by both Natural and Sexual Selection in 

 the production of diverse species from one original stock. I am 

 inclined to think that developmental variation has been more im- 

 portant in the origin of species than has abnormal, or as Darwin 

 calls it, 'spontaneous,' variation. The transmission of such ab- 

 normal variations as supernumerary digits seems to be so much more 

 uncertain than the transmission of developmental variation, while 

 practically speaking the origin of Ammonite species seems to be 

 almost entirely attributable to developmental variation. 



"Specialized structures like the long neck of the giraffe and the 

 proboscis of the elephant, to take familiar instances, are, in my 

 opinion, developmental variations. They did not arise, in the first 

 place, in certain members of the pregiraffian or preelephantine 

 species as abnormal or ' spontaneous ' variations which gave their 

 possessors such great superiority over their fellows in the struggle 

 for existence that those possessors survived by the law of Natural 

 Selection. These features began imperceptibly — the neck and the 

 nose grew more in proportion to other features during the lives of 

 the individuals on account of the habits of the animals, and they 

 may be compared in this respect to the enlarging skull of civilized 

 Man. 



"As the features of the adult become in course of time the fea- 

 tures of the adolescent by the law of earlier inheritance, the elon- 

 gation of nose and neck would become exaggerated from one 

 generation to another. I do not see any reason to suppose, at any 

 .rate at first, that the girafflan or elephantine ancestors were the 

 favored individuals of the community, and that the other members 

 died out because they did not possess elongatled necks or noses. 

 J do not suppose that all the members of the species possessed 



