vii HEREDITY, VARIATION 103 



the offspring of any two parents derive, on the average, 

 one-half of their characteristics from those parents, one- 

 fourth from their four grandparents, 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 

 well-known fact that certain peculiarities of body or of 

 character are apt to reappear in families during several 

 centuries. 



Now this simple law explains almost all the facts includ- 

 ing the apparent failures of inheritance all its irregularities 

 in individual cases, together with its constancy and regularity 

 when large numbers are examined. It shows us why, when 

 families for several generations have been noted for beauty, 

 for stature, for strength, or for talent, these characters will 

 almost certainly be found developed in most of their 

 children, who from three or four generations of ancestors 

 have a good chance of deriving seven-eighths or fifteen- 

 sixteenths of their entire organisations. If, on the other 

 hand, the beauty or talent of parents were exceptional in 

 their respective families, then their children, having a number 

 of commonplace or inferior ancestors, would 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. 



From this consideration there is deduced another general 

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

 apparent deviations or incongruities. This is called the 

 " law of recession towards mediocrity." It means that, 

 whenever parents deviate considerably from the average of 

 the population of which they form a part, their offspring 

 will tend to return towards the average. For example, 

 if both parents are decidedly below or above the average in 

 height, in beauty of form, in any special faculty, as music, 

 drawing, etc., their children will usually go back towards 

 the average, though still retaining some of the parental 

 excess or defect. It is owing to this law that very extreme 

 developments, whether of body or of mind gigantic stature 

 or supreme genius are rarely transmitted to the next 



