82 THE ORIGIN OF SPECIES 



offspring in successive generations are eminently liable 

 to vary, as every experimentalist has observed. 



Thus we see that when organic beings are placed 

 under new and unnatural conditions, and when hybrids 

 are produced by the unnatural crossing of two species, 

 the reproductive system, independently of the general 

 state of health, is affected in a very similar manner. In 

 the one case, the conditions of life have been disturbed, 

 though often in so slight a degree as to be inappreciable 

 by us; in the other case, or that of hybrids, the external 

 conditions have remained the same, but the organization 

 has been disturbed by two distinct structures and consti- 

 tutions, including of course the reproductive systems, 

 having been blended into one. For it is scarcely possible 

 that two organizations should be compounded into one, 

 without some disturbance occurring in the development, 

 or periodical action, or mutual relations of the different 

 parts and organs one to another or to the conditions of 

 life. When hybrids are able to breed inter se, they 

 transmit to their offspring from generation to generation 

 the same compounded organization, and hence we need 

 not be surprised that their sterility, though in some 

 degree variable, does not diminish; it is even apt to 

 increase, this being generally the result, as before ex- 

 plained, of to() close interbreeding. The above view of 

 the sterility of hybrids being caused by two constitutions 

 being compounded into one has been strongly maintained 

 by Max Wichura. 



It must, however, be owned that we cannot under- 

 stand, on the above or any other view, several facts with 

 respect to the sterility of hybrids; for instance, the 

 unequal fertility of hybrids produced from reciprocal 



