Chap. XVII, CONCLUSION. 125 



of the same family were to be the victorious successor. The 

 structure of many of the lower animals, when they are 

 hermaphrodites, is such as to prevent the ovules being fer- 

 tilised by the male element of the same individual ; so that 

 the concourse of two individuals is necessary. In other cases 

 the access of the male element of a distinct individual is 

 at least possible. With plants, which are affixed to the 

 ground and cannot wander from place to place like animals, 

 the numerous adaptations for cross-fertilisation are wonder- 

 fully perfect, as has been admitted by every one who has 

 studied the subject. 



The evil consequences of long-continued close interbreeding 

 are not so easily recognised as the good effects from crossing, 

 for the deterioration is gradual. Nevertheless, it is the 

 general opinion of those who have had most experience, 

 especially with animals which propagate quickly, that evil 

 does inevitably follow sooner or later, but at different rates 

 with different animals. No doubt a false belief may, like a 

 superstition, prevail widely ; yet it is difficult to suppose that 

 so many acute observers have all been deceived at the expense 

 of much cost and trouble. A male animal may sometimes be 

 paired with his daughter, granddaughter, and so on, even for 

 seven generations, without any manifest bad result : but the 

 experiment has never been tried of matching brothers and 

 sisters, which is considered the closest form of interbreeding, 

 for an equal number of generations. There is good reason to 

 believe that by keeping the members of the same family in 

 distinct bodies, especially if exposed to somewhat different 

 conditions of life, and by occasionally crossing these families, 

 the evil results of interbreeding may be much diminished or 

 quite eliminated. These results are loss of constitutional 

 vigour, size, and fertility ; but there is no necessary dete- 

 rioration in the general form of the body, or in other good 

 qualities. We have seen that with pigs first-rate animals 

 have been produced after long-continued close interbreeding, 

 though they had become extremely infertile when paired 

 with their near relations. The loss of fertility, when it 

 occurs, seems never to be absolute, but only relative to 

 animals of the same blood ; so that this sterility is to a certain 



