Chap. XXVIII. 



CONCLUDING EEMARKS. 



423 



I have just said that the crossed offspring would gain in 

 vigour and fertility. From the facts given in the seventeenth 

 chapter there can be no doubt of this ; and there can be 

 little doubt, though the evidence on this head is not so easily 

 acquired, that long-continued close interbreeding leads to evil 

 results. With hermaphrodites of all kinds, if the sexual ele- 

 ments of the same individual habitually acted on each other, 

 the closest possible interbreeding would be perpetual. There- 

 fore we should bear in mind that with all hermaphrodite 

 animals, as far as I can learn, their structure permits and 

 frequently necessitates a cross with a distinct individual. With 

 hermaphrodite plants we incessantly meet with elaborate and 

 perfect contrivances for this same end. It is no exaggeration 

 to assert that, if the use of the talons and tusks of a carnivorous 

 animal, or the use of the viscid threads of a spider's web, or of 

 the plumes and hooks on a seed may be safely inferred from 

 their structure, we may with equal safety infer that many flowers 

 are constructed for the express purpose of ensuring a cross with 

 a distinct plant. From these various considerations, the con- 

 clusion arrived at in the chapter just referred to — namely, that 

 great good of some kind is derived from the sexual concourse of 

 distinct individuals — must be admitted. 



To return to our illustration : we have hitherto assumed that 

 the birds were kept down to the same number by indiscriminate 

 slaughter ; but if the least choice be permitted in their preser- 

 vation and slaughter, the whole result will be changed. Should 

 the owner observe any slight variation in one of his birds, 

 and wish to obtain a breed thus characterised, he would succeed 

 in a surprisingly short time by carefully selecting and pairing 

 the young. As any part which has once varied generally goes 

 on varying in the same direction, it is easy, by continually pre- 

 serving the most strongly marked individuals, to increase the 

 amount of difference up to a high, predetermined standard 

 of excellence. This is methodical selection. 



If the owner of the aviary, without any thought of making 

 a new breed, simply admired, for instance, short-beaked more 

 than long-beaked birds, he would, when he had to reduce the 

 number, generally kill the latter; and there can be no doubt 

 that he would thus in the course of time sensibly modify his 



