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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 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. Iam 
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 preélephantine 
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 girafhan or elephantine ancestors were the 
favored individuals of the community, and that the other members 
died out because they did not possess elongated necks or noses. 
I do not suppose that all the members of the species possessed 
