120 REVERSION AND ALLIED PHENOMENA 



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. 



Darwin believed that " an inherent tendency to reversion is 

 evolved through some disturbance in the organisation caused by 

 the act of crossing," and he gave such instances as the following. 

 A goldfinch crossed with a plain yellow canary had offspring with 

 stripes on the back and flanks. Darwin concluded that " this 

 streaking must be derived from the original wild canary." He 

 crossed a White Silkie hen with a black Spanish cock and got 

 among the progeny a cock which looked like a rehabilitation of 

 the original wild Callus bankiva type. These facts have been 

 confirmed, but it is now generally agreed that the Darwinian in- 

 terpretation of them must give place to the Mendelian that " in 

 hybridising we restore the factor that is missing from one strain 

 by introducing it from another strain ; or we remove the added 

 factor that veils the ancestral condition " (Davenport, 1910, p. 293, 

 "The New Views about Reversion"). 



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. 



