ATAVISM. 81 



present an assemblage of characters quite different 

 from those that characterize the parents. These have 

 been explained on the supposition that there must be 

 a law of " spontaneity " which is antagonistic to that 

 of heredity, or that the law of heredity is not constant 

 in its action, but limited by numerous exceptions. 1 



The view we have presented of the law of inheri- 

 tance would seem to preclude the necessity of any 

 such hypothesis to account for the individual varia- 

 tions referred to. Many of the cases of supposed 

 variation are fully explained on the principle of atavic 

 descent, which is, as we have seen, but a phase of the 

 great law of heredity. 



If characters are transmitted as physiological units, 

 it will be readily seen that, although an animal may 

 be composed of precisely the same elements as its an- 

 cestors, the dominance of some of these, or the ar- 

 rangement of the elements themselves, must give rise 

 to individual peculiarities, or even to forms not pre- 

 cisely identical with those, exhibited in the dominant 

 characters of any ancestor. Any observed variations 

 in the inheritance of form, color, or general character- 

 istics, may thus be readily accounted for, within the 

 limits of the characters belonging to the ancestors. 



In these cases of apparent variation, the similarity 

 of the offspring to its ancestors consists in the posses- 

 sion of the same assemblage of characters which is 

 often shown in a general rather than a special resem- 

 blance. From the complexity of the elements trans- 

 mitted from generation to generation, we cannot ex- 

 pect the offspring, in a particular case, to be the exact 



1 Ribot on " Heredity," p. 194, etc. 



