

362 PROVISIONAL HYPOTHESIS Chap. XXVII. 



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From the several foregoing considerations we may conclude 



that the difference between sexual and asexual generation is 

 not nearly so great as it at first appears ; and we have already 

 seen that there is the closest agreement between gemmation, 



fissiparous generation, the repair of injuries, and ordinary growth 



or development. The capacity of fertilisation by the male 

 element seems to be the chief distinction between an ovule and 

 a bud ; and this capacity is not invariably brought into action, 

 as in the cases of parthenogenetic reproduction. We are here 

 naturally led to inquire what the final cause can be of the 

 necessity in ordinary generation for the concourse of the t\fo 

 sexual elements. 



Seeds and ova are often [highly serviceable as the means of 

 disseminating plants and animals, and of preserving them durino- 

 one or more seasons in a dormant state; but unimpregnated 

 seeds or ova, and detached buds, would be equally serviceable 

 for both purposes. We can, however, indicate two important 

 advantages gained by the concourse of the two sexes, or rather 

 of two individuals belonging to opposite sexes ; for, as I have 

 shown in a former chapter, the structure of every organism 

 appears to be especially adapted for the concurrence, at least 

 occasionally, of two individuals. In nearly the same manner 

 as it is admitted by naturalists that hybridism, from inducing 

 sterility, is of service in keeping the forms of life distinct and 

 fitted for their proper places; so, when species are rendered 

 highly variable by changed conditions of life, the free inter- 

 crossing of the varying individuals will tend to keep each form 

 fitted for its proper place in nature ; and crossing can be effected 

 only by sexual generation, but whether the end thus gained 

 is of sufficient importance to account for the first origin of 

 sexual intercourse is very doubtful. Secondly, I have shown, 

 from the consideration of a large body of facts, that, as a slight 

 change m the conditions of life is beneficial to each creature, 

 so, m an analogous manner, is the change effected in the germ 

 by sexual union with a distinct individual ; and I have been led, 

 from observing the many widely-extended provisions throughout 

 nature for this purpose, and from the greater vigour of crossed 

 organisms of all kinds, as proved by direct experiments, as 

 well as from the evil effects of close interbreeding when long 



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