VARIATION. 261 



animals of the same species, we see the contrast, that though 

 the homogeneous wild race maintains its typo with great per- 

 sistence, the comparatively heterogeneous domestic race fre- 

 quently produces individuals more unlike the average type 

 than the parents are. 



Though unlikeness among progenitors is one antecedent 

 of variation, it is by no means the sole antecedent. Were 

 it so, the young ones successively born to the same parents 

 would be alike. If any peculiarity in a new organism 

 were a direct resultant of the structural differences between the 

 two organisms which produced it ; then all subsequent new 

 organisms produced by these two, would show the same pecu- 

 liarity. But we know that the successive offspring have differ- 

 ent peculiarities : no two of them are ever exactly alike. 



One cause of such structural variation in progeny, is 

 functional variation in parents. Proof of this is given by 

 the fact that, among the progeny of the same parents, there is 

 more difference between those begotten under different con- 

 stitutional states, than between those begotten under the 

 same constitutional state. It is notorious that twins are 

 more nearly alike than children borne in succession. The 

 functional conditions of the parents being the same for twins, 

 but not the same for their brothers and sisters (all other ante- 

 cedents being constant) ; we have no choice but to admit that 

 variations in the functional conditions of the parents, are the 

 antecedents of those greater unlikenesses which their brothers 

 and sisters exhibit. 



Some other antecedent remains, however. The parents 

 being the same, and their constitutional states the same, va- 

 riation, more or less marked, still manifests itself. Plants 

 grown from seeds out of one pod, and animals produced at 

 one birth, are not alike ; and sometimes differ considerably. 

 In a litter of pigs or of kittens, we rarely see uniformity of 

 markings ; and occasionally, there are important structural 

 contrasts. I have myself recently been shown a litter of 

 Newfoundland puppies, some of which had four digits to 



