1900.] on Facts of Inheritance. 355 



may persist without combining. We have extended the wide con- 

 ception of the struggle for existence in many directions ; it may be 

 between organisms akin or not akin, between plants and animals, 

 between organisms and their inanimate environment, between the 

 sexes, between the different parts of the body, between the ova, 

 between the spermatozoa, between the ova and the spermatozoa, and 

 Weismann has suggested that it may also be between the constituents 

 of the germ-plasm. 



IV. Eegbession. 



We have already referred to the fact which stares ns in the face 

 that there is a sensible stability of type from generation to genera- 

 tion. " The large," Mr. Gal ton 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, weeding out 

 abnormalities, often before they are born. But it is to be primarily 

 accounted for by what Mr. Galton calls the fact of " filial regres- 

 sion." Let me take an instance from Mr. Pearson's ' Grammar of 

 Science.' Take fathers, of stature 72 inches, the mean height of their 

 sons is 70*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 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." 



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

 sustaining of the specific average is certainly not due to each indi- 

 vidual leaving his like behind him, for we all know that this is not 

 the case. It is due to a regression which tends to bring the offspring 

 of extraordinary parents nearer the average of the stock. In other 

 words, children tend to differ less from mediocrity than their parents. 



This big average fact is to be accounted in terms of that genetic 

 continuity which makes an inheritance not dual, but multiple. " A 

 man," says Mr. Pearson, " is not only the product of his father, but 

 of all his past ancestry, and unless very careful selection has taken 

 place, the mean of that ancestry is probably not far from that of the 

 general population. In the tenth generation a man has [theoretically] 

 1024 tenth great-grandparents. He is eventually the product of a 

 population of this size, and their mean can hardly differ from that 

 of the general population. It is the heavy weight of this mediocre 

 ancestry which causes the son of an exceptional father to regress 

 towards the general population mean ; it is the balance of this sturdy 



