122 REVERSION AND ALLIED PHENOMENA 



closely than its immediate parents, our attention is not much 

 arrested, though in truth the fact is highly remarkable ; but when 

 the child resembles some remote ancestor, or some distant member 

 in a collateral line — and we must attribute the latter case to the 

 descent of all the members from a common progenitor — we feel a 

 just degree of astonishment. When one parent alone displays 

 some newly acquired and generally inheritable character, and the 

 offspring do not inherit it, the cause may lie in the other parent 

 having the power of prepotent transmission. But when both 

 parents are similarly characterised, and the child does not, whatever 

 the cause may be, inherit the character in question, but resembles 

 its grandparents, we have one of the simplest cases of reversion." 



" The most simple case of reversion — namely, of a hybrid or mongrel 

 to its grandparents — is connected by an almost perfect series with 

 the extreme case of a purely bred race recovering characters which 

 had been lost during many ages ; and we are thus led to infer that 

 all the cases must be related by some common bond " (ihid. p. 49). 



" By the term reversion," Weismann says, " is meant the appear- 

 ance of characteristics which existed in the move remote ancestors, 

 but were absent in the zmmet^za/g ancestors — i.e. the parents" (1893, 

 p. 299). 



Prof. Karl Pearson defines a reversion as " the full reappearance 

 in an individual of a character which is recorded to have oc- 

 curred in a definite ancestor of the same race," and atavism as " a 

 return of an individual to a character not typical of the race at all, 

 but found in allied races supposed to be related to the evolutionary 

 ancestry of the given race. ... In reversion we are considering a 

 variation, normal or abnormal, from the standpoint of heredity in 

 the individual ; in atavism we are considering an abnormal variation 

 from the standpoint of the ancestry of the race." But as the two 

 words have been used by some authors in the converse way, and as 

 it is surely difficult to define the field of abnormal variation, we 

 adhere to Darwin's wider usage, and drop the term " atavism " as 

 an unnecessary synonym. 



" Reversion," De Vries says, " means the falling back or returning 

 to another type, and the word itself expresses the idea that this latter 

 type is the form from which the variety has arisen. . . . Atavism 

 or reversion is the falling back to a prototype " — i.e. " those an- 

 cestors from which a form is known to have been derived." But 

 De Vries distinguishes sharply between true reversion due to a 



