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though why it does so is not clear. By such process, however, 
there arise both males and females which possess characters 
different to those which their ancestors possessed. 
By the time that this character, influenced by the law of 
earlier inheritance, appears at an age early enough to be 
transferred to the female, the male has probably either further 
elaborated this character—which further elaboration is at first 
transmitted to the males only—or he has elaborated some- 
thing else so much that it seems like a new character, which 
is transmitted in the same way. In course of time this further 
elaboration, or this new character as the case may be, is 
transmitted also to the females; and so it becomes plain how, 
merely by the gradual transmission of developmental variations, 
both sexes of what may be called an incipient species, beginning 
with a slight variation in one sex alone, are able to diverge 
wider and wider from the original stock. 
The same laws of transmission would of course hold good 
if 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 
developmental variations transmitted in accordance with the 
law of earlier 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 develop- 
mental variation has been more important in the origin of 
species than has abnormal, or as Darwin calls it “spontaneous” 
variation. The transmission of such abnormal variations as 
supernumary 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. 
