Tlie Evidence from Variation. 151 



gaged in conducting the operations of the Real del 

 Monte Company in Mexico, carried out with them some 

 greyhounds of the best breed to hunt the hares which 

 abound in that country. It was found that the grey- 

 hounds could not support the fatigues of a long chase 

 in this attenuated atmosphere, and before they could 

 come up with their prey they lay down gasping for 

 breath; but these same animals have produced whelps, 

 which have grown up, and are not in the least degree 

 incommoded by the want of density of the air, but run 

 down the hares with as much ease as do the fleetest of 

 their race in this country. 



It is interesting to note in this connection that a 

 tendency to vary is strongly inherited independently of 

 the inheritance of any particular variation. . Darwin 

 believes that this tendency to vary may be transmitted 

 by either parent, and he says ( Variation, ii. 325) it 

 is certain that variability may be transmitted through 

 either sexual element, whether or not originally excited 

 in them, for Kolreuter and Gartner found that when 

 two species were crossed, if either one was variable the 

 offspring were rendered variable. 



We have already pointed out that the crossing of 

 species is in itself one of the most efficient causes of 

 variation, and we can hardly base upon the observations 

 above given the conclusion that variability may be trans- 

 mitted by either sex. 



The fact that changed conditions do not directly pro- 

 duce variation, but cause subsequent generations to 

 vary, is precisely what we should expect, according to 

 our theory: for a change in the environment of an ani- 

 mal or plant must disturb the harmonious adjustment 

 which natural selection has brought about between the 

 cells of its body and their conditions of life. Such a 



