8o Heredity and Environment 



the four grand-parents is usually unequal and the farther back 

 we go the more ancestors we find who have contributed nothing 

 to our inheritance. Of all the thousands or even millions of an- 

 cestors that each of us has had, only a relatively small number 

 have contributed anything to our inheritance; although we are 

 descended from all the others we are not related to them bio- 

 logically and have received none of their traits. Those who have 

 contributed to our . inheritance may be called "contributing an- 

 cestors" or merely "contributors"* to distinguish them from non- 

 contributing ones, and the fact that ancestors do not contribute 

 equally to heredity disproves Galton's "law of ancestral inherit- 

 ance." 



2. The Law of Filial Regression is the second principle which 

 Galton deduced from his statistical studies, or it may be called 

 the tendency to mediocrity. He found that, on the average, ex- 

 treme peculiarities of parents were less extreme in children. 

 Thus, "the stature of adult offspring must on the whole be more 

 mediocre than the stature of their parents, that is to say more 

 near to the mean or mid of the general population" ; and again, 

 "the more bountifully a parent is gifted by nature, the more rare 

 will be his good fortune if he begets a son who is as richly en- 

 dowed as himself." This so-called law of filial regression is 

 represented graphically in Fig. 25 in which the actual stature of 

 individual parents is shown by the oblique line, the stature of 

 children by the dotted curve, and the mean stature of the race in 

 the horizontal dotted line. 



Statistical vs. Physiological Methods. One of the chief aims 

 and results of statistical studies is to eliminate individual peculiari- 

 ties and to obtain general and average results. Such work may 

 be of great importance in the study of heredity, especially where 

 questions of the occurrence or distribution of particular phenomena 

 are concerned; but the causes of heredity are individual and 



* I have adopted this term proposed by Dr. H. H. Laughlin in prefer- 

 ence to "transmitters" which I had previously used. 



