iz8 REVERSION AND ALLIED PHENOMENA 



pressed in parents or grandparents, but known to occur in more 

 or less remote ancestors, we must try to discover how far this 

 peculiarity is really fart of the inheritance. That is to say, 

 we must inquire whether it may not be a modification induced 

 from without, which happens to resemble an innate character 

 of the ancestors. Many domesticated animals which have 

 become wild (feral) may show features resembling the original 

 wild ancestor, but these may be due to the direct influence of 

 the old environment and the old functions. It is safe to say that 

 many of the so-called reversions of feral animals are not inborn 

 but acquired and modificational. 



Filial Regression. — We shall afterwards consider (Chapter IX.) 

 Mr. Galton's Law of Filial Regression, but it must be noticed 

 here, if only to point out that it has nothing to do with reversion. 

 The law, concretely stated, is that offspring are not likely to 

 differ from mediocrity in a given direction so widely as their 

 parents do in the same direction. There is a continual tendency 

 to sustain a specific average, or a stock-average. 



Let us take a simple instance from Prof. Karl Pearson's 

 Grammar of Science. Suppose a group of fathers with a stature 

 of 72 in. : the mean height of their sons is 70*8 in. — a regression 

 towards the mean height of the general population. On the 

 other hand, fathers with a mean height of 66 in. give a group 

 of sons of mean height 683 in. — again nearer the mean height 

 of the general population. The " regression " works both ways ; 

 there is a levelling-up as well as a levelling-down. " The father 

 with a great excess of the character contributes sons with an 

 excess, but a less excess of it ; the father with a great defect of 

 the character contributes sons with a defect, but less of it." 



Now this very important and normal fact of filial regression 

 has nothing to do with reversion, which implies the reappear- 

 ance of a definite ancestral character or set of characters which 

 have " lain latent " for several generations. 



Independent Variations resembling Reversions. — If we 



