124 Species; or, Darwinism. 



generation revert to one or other of the specific 

 types which were crossed. Then they never re- 

 sume the other type, as if they had rejected all par- 

 ticipation in a mixed specific nature. This is the 

 phenomenon of Reversion. Others, which do not 

 revert, throw all calculations about them into a 

 distressing state of confusion, by showing extra- 

 ordinary and mutually divergent variations. This 

 is the phenomenon called Disordered Variation; 

 and it testifies to the irregularity which has been 

 put upon nature and which is continued through 

 man's interference. Fifthly, there is only one 

 hope, at length, of the hybrid progeny surviving, 

 ancl that is by absolute reversion to one or other 

 parental type; so that the case, as one of hybrida- 

 tion, is utterly extinguished. With mongrels (No. 

 133), on the contrary, the fertility is even increased 

 by the mixing of races; and, when a distinctive race 

 has been formed, individuals may still at any time 

 reproduce as native traits the special characters of 

 one or other parental race, which originally blended 

 to form this mongrel new one. Such a reproduc- 

 tion of ancestral traits is called Atavism. 



135. The variability which gives rise to varieties 

 and races as the result of self-adjustment to the 

 environment, is not restricted to any single organ, 

 which adjusts itself in that manner. A proportion- 

 ate adaptation takes place in other parts also. This 

 might be understood from what we said before on 

 acclimatization and naturalization (No. 77, 78). 



