I20 REVERSICN AND ALLIED FHENOMEAA 



seems to us, entirely legitimate. When we go beyond the use 

 of the word as a descriptive term, and use it as implying that 

 the ancestral characters reappear because they are parts of 

 the inheritance, which have been lying latent for generations, 

 and have suddenly been allowed by some liberating stimulus to 

 express themselves in development, we pass from fact to inter- 

 pretation, from description to theory, and great care is necessary. 

 For the fact that an organism exhibits some peculiarity character- 

 istic of an ancestor does not necessarily imply that this is due to 

 the rehabilitation of latent items in its inheritance. Although 

 we shall seek in this chapter to show that there are reversions 

 in the strict theoretical sense, we shall also point out that many 

 phenomena have been called reversions in a loose descriptive 

 sense which is often misleading. Thus we have much sympathy 

 with Mr. Bateson's remark : " Around the term ' reversion ' a 

 singular set of false ideas have gathered themselves. ... It 

 would probably help the science of biology if the word ' reversion ' 

 and the ideas it denotes were wholly dropped, at all events until 

 variation has been studied much more fully than it has yet 

 been " {Materials for the Study of Variation, p. 78). 



If we keep the term as a purely descriptive one, there is no 

 doubt as to the occurrence of what may be called " reversions." 

 But difficulties immediately arise when we ask whether all the 

 phenomena so described are really of the same kind, and when 

 we try to interpret them theoretically. 



Illustrations. — A recognition of reversionary or atavistic phenomena 

 is ancient. Plutarch gives the case of a Greek married woman who, 

 having given birth to a black child, was brought to justice as an 

 adulteress, and had science enough to allege in her defence that 

 she was descended from an Ethiopian four generations back. This is 

 paralleled by a case reported by De Quatrefages of two Virginian 

 slaves, to whom a perfectly white child was born. " En voyant la 

 couleur de son enfant, elle fut saisie de terreur, . . . mais son mari 

 la rassura, en lui declarant que son propre frere etait blanc." 



We do not mean that the instances just mentioned should be 



