408 PROGRESS OF SCIENCE IN THE CENTURY. 



on one side, and a maternal eye on the other. Sup- 

 pose the parents of a foal to be markedly light and 

 dark in colour; if the foal is light brown the in- 

 heritance in that respect is blended, if light or dark 

 it is exclusive, if piebald it is particulate. In the 

 last case there is in the same character an exclusive 

 inheritance from both parents. 



(IV.) Regression. — To Mr. Frances Galton espe- 

 cially we owe an analysis of the fact which stares us 

 in the face that there is a sensible stability of type 

 from generation to generation. " The large," he 

 says, " do not always beget the large, nor the small 

 the small; but yet the observed proportion between 

 the large and the small, in each degree of size and in 

 every quality, hardly varies from one generation to 

 another.'^ In other words, there is a tendency to 

 keep up a specific average. This may be partly due 

 to the action of natural elimination, w^eeding out 

 abnormalities, often before they are born. But it 

 is to be primarily accounted for by what Mr. Galton 

 calls the fact of " filial regression.'' Let us take 

 an instance from Mr. Pearson's Grammar of Sci- 

 ence. • Take fathers, of stature 72 inches, the mean 

 height of their sons is Y0.8, we have a regression 

 towards the mean of the general population. On the 

 other hand, fathers with a mean height of 66 inches 

 give a group of sons of mean height 68.3 inches, 

 again nearer the mean. " The father with a great 

 excess of the character contributes sons with an ex- 

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

 defect of the character contributes sons with a de- 

 fect, but less of it." 



As Mr. Galton puts it, society moves as a vast 

 fraternity. The sustaining of the specific average 

 is certainly not due to each individual leaving his 



