626 APPENDIX B. 



All the lambs produced strikingly resembled each other, and even Englishmen 

 took them for animals of their own country." 



M. Nouel goes on to remark that when this derived breed was 

 bred with itself, the marks of the French breeds were lost. 

 "Some slight traces" could be detected by experts, but these 

 " soon disappeared." 



Thus we get proof that relatively pure constitutions predomi- 

 nate in progeny over mnch mixed constitutions. The reason is 

 not difficult to see. Every organism tends to become adapted to 

 its conditions of life ; and all the structures of a species, accus- 

 tomed through multitudinous generations to the climate, food, 

 and various influences of its locality, are moulded into harmonious 

 co-operation favourable to life in that locality : the result being 

 that in the development of each young individual, the tendencies 

 conspire to produce the fit organization. It is otherwise when 

 the species is removed to a habitat of different character, or when 

 it is of mixed breed. In the one case its organs, partially out of 

 harmony with the requirements of its new life, become partially 

 out of harmony with one another ; since, while one influence, say 

 of climate, is but little changed, another influence, say of food, is 

 much changed ; and, consequently, the perturbed relations of the 

 organs interfere with their original stable equilibrium. Still more 

 in the other case is there a disturbance in equilibrium. In a 

 mongrel, the constitution derived from each source repeats itself 

 as far as possible. Hence a conflict of tendencies to evolve two 

 structures more or less unlike. The tendencies do not harmoni- 

 ously conspire, but produce partially incongruous sets of organs. 

 And evidently where the breed is one in which there are united 

 the traits of various lines of ancestry, there results an organiza- 

 tion so full of small incongruities of structure and action, that it 

 has a much-diminished power of maintaining its balance; and 

 while it cannot withstand so well adverse influences, it cannot so 

 well hold its own in the offspring. Concerning parents of pure 

 and mixed breeds respectively, severally tending to reproduce 

 their own structures in progeny, we may therefore say, figura- 

 tively, that the house divided against itself cannot withstand the 

 house of which the members are in concord. 



Now if this is shown to be the case with breeds the purest of 

 which have been adapted to their habitats and modes of life dur- 

 ing some few hundred years only, what shall we say when the ques- 

 tion is of a breed which has had a constant mode of life in the 

 same locality for ten thousand years or more, like the quagga ? 

 In this the stability of constitution must be such as no domestic 

 animal can approach. Relatively stable as may have been the 

 constitutions of Lord Morton's horses, as compared with the con- 

 stitutions of ordinary horses, yet, since Arab horses, even in their 



