474 LIFE : OUTLINES OF GENERAL BIOLOGY 



invariably follow a cross are from the first manifest. (3) It should, 

 however, be clearly understood that the advantage of close inter- 

 breeding, as far as the retention of character is concerned, is indis- 

 putable, and often outweighs the evil of a slight loss of constitutional 

 vigour." 



From his researches on flowering plants, Darwin concluded that 

 there was "something injurious" connected with self- fertilisation; 

 and although he came to recognise that self- fertilisation was more 

 frequent and more successful than he had at first believed, he 

 adhered on the whole to the aphorism, "Nature abhors perpetual 

 self- fertilisation". In his book on Cross and Self- Fertilisation (1876), 

 however, he says: "If the word 'perpetual' had been omitted, the 

 aphorism would have been false. As it stands, I believe that it is 

 true, though perhaps rather too strongly expressed." His general 

 conclusion was that self-fertilisation in flowers is for the mo.st part 

 relatively, but not absolutely, injurious. 



There is little biological evidence to show that there is anything 

 necessarily disadvantageous or dangerous in close consanguineous 

 unions. These seem often to occur in nature in isolated and restricted 

 areas, and they are frequent in successful breeding. It must be 

 admitted that evil effects sometimes follow prolonged consanguineous 

 pairing in the artificial conditions of stockbreeding. but it must not 

 be hastily inferred that these evil effects are necessarily due to the 

 consanguinity. There may be persistence of unwholesome conditions 

 of life which have a cumulative evil effect as generation succeeds 

 generation, or there may be some organic taint in the early members 

 of the stock which becomes aggravated, just as a desirable organic 

 peculiarity may be enhanced. 



Bateson expressed the view of most biologists when he said : 



"It should perhaps be pointed out categorically that nothing in 

 our present knowledge can be taken with any confidence as a 

 reason for regarding consanguineous marriage as improper or 

 specially dangerous. All that can be said is that such marriages 

 give extra chances of the appearance of recessive characteristics 

 among the offspring. Some of these are doubtless bad qualities, 

 but we do not yet know that among the recessives there may not 

 be valuable qualities also" {Mendel's Principles of Heredity, new 

 edition, London, 1909, p. 226). 



The whole subject has been illumined by East and Jones in their 

 fine work. Inbreeding and Outbreeding (1919). It is convincingly 

 shown that inbreeding of good stock, accompanied by judicious 

 elimination of "wasters", fixes desirable characters, and tends to 

 a stable and uniform herd. That it is sometimes aussociated with 

 reduction of vigour, resisting power, fecundity, and even size, 

 cannot be denied. Hut this is not because of the consanguinity as 

 such, but because the inbreeding automatically brings into expres- 



