HEREDITY, VARIATION 111 



V 



ance under normal conditions. It is that the offspring of any 

 two parents derive, on the average, one-half of their character- 

 istics from tliose parents, one-fourth from their four grand- 

 parents, one-eighth from their eight great-grandparents, and 

 so on to remote ancestry, the total result being that one-half 

 of each individual's peculiarities is derived from its parents, 

 while the other half comes from its whole previous ancestry. 

 Hence arises the Avell-known fact that certain peculiarities of 

 body or of character are apt to reappear in families during 

 several centuries. 



Xow this simple law explains almost all the facts including 

 the apparent failures of inheritance — all its irregularities in in- 

 dividual cases, together with its constancy and regularity when 

 larse numbers are examined. It shows us whv, when families 

 for several generations have been noted for beauty, for stature, 

 for strength, or for talent, these characters will almost cer- 

 tainly be found developed in most of their children, who from 

 three or four generations of ancestors have a good chance of de- 

 riving seven-eighths or fifteen-sixteenths of their entire or- 

 ganisations. If, on the other hand, the beauty or talent of 

 jjarents were exceptional in their respective families, then 

 iheir children, having a number of commonplace or inferior 

 ancestors, w^ould often be far inferior to their parents in the 

 particulars in which the parents excelled, and in their case 

 heredity would seem to have failed. 



Erom this consideration there is deduced another general 

 law, very easy to remember and of great use in explaining ap- 

 parent deviations or incongruities. This is called the '^ law" of 

 recession towards mediocrity." It means that, whenever par- 

 ents deviate considerably from the average of the population 

 of which they form a part, their offspring will tend to return 

 towards the average. Eor example, if both parents are de- 

 cidedly below or above the average in height, in beauty of 

 form, in any special faculty, as music, drawing, etc., their chil- 

 dren will usuallv ffo back towards the averaii'e, thou2:li still re- 

 taining some of the parental excess or defect. It is owing to 



