252 THE CROSSING, &C, OP PIGEONS AND FOWLS. 



pletely shattered constitutions, and with sterility, before 

 they have half accomplished such process of diver- 

 gence ! 



Not only do the phenomena of close-interbreeding, 

 constitute an insuperable bar to any such result as evo- 

 lution, into distinct species, by means of this divergence; 

 but, the man is likewise blocked, in the other direction, 

 by the fact of the sterility of hybrids ! 



If the proofs of reversion, the phenomena of close- 

 interbreeding, the phenomena of crossing, and the fact 

 of the sterility of hybrids, do not constitute the elements 

 of a complete demonstration; then a demonstration is 

 impossible, without the domain of mathematics. 



Again, he says (p. 150, Vol. ii, Animals and Plants, 

 &c): 



" With all highly bred animals " (he here obviously 

 speaks of the animals which are divergent in charac- 

 ter; for, he elsewhere says, "with animals not divergent 

 in character, such as cattle and sheep, interbreeding may 

 be long carried vn without any decrease in fertility or 

 vigor"), "with all highly bred animals, there is more or 

 less difficulty, in getting them to procreate quickly, and 

 all suffer much from delicacy of constitution ; but, I do 

 not pretend that these effects ought to be wholly at- 

 tributed to close-interbreeding." 



Strictly speaking, no evil is to be attributed to 

 close-interbreeding. It is disproportionate develop- 

 ment which causes the evil : Close-interbreeding but 

 aggravates such evil. The " difficulty," of which he 

 speaks, " in getting highly-bred animals to procreate," 

 and their "delicacy of constitution," are in proportion to 

 divergence of character, or rather to defects in struc- 



