

2 Life and Letters of Francis Galton 



simply and wholly caused by A , nor indeed by C, D, E and F as well ! It 

 was really possible to go on increasing the number of contributory causes, 

 until they might involve all the factors of the universe. The physicist was 

 clearly picking out a few of the more important causes of A, and wisely con- 

 centrating on those. But no two physical experiments would — even if our 

 instruments of measurement, men and machines, were perfect — ever lead to 

 absolutely the same numerical result, because we could not include all the 

 vast range of minor contributory causes. The physicist's method of describing 

 phenomena was seen to beonlyfitting whenahigh degree of correlation existed. 

 In other words he was assuming for his physical needs a purely theoretical 

 limit — that of perfect correlation. Henceforward the philosophical view of the 

 universe was to be that of a correlated system of variates, approaching but by 

 no means reaching perfect correlation, i.e. absolute causality, even in the group 

 of phenomena termed physical. Biological phenomena in their numerous 

 phases, economic and social, were seen to be only differentiated from the 

 physical by the intensity of their correlations. The idea Galton placed before 

 himself was to represent by a single numerical quantity the degree of 

 relationship, or of partial causality, between the different variables of our 

 ever-changing universe. How far he was successful forms the subject-matter 

 of this chapter. 



I have said that Galton came to this fundamental conception from two 

 aspects. The first problem was that of inheritance. To take an illustration : 

 A character in the Father does not determine absolutely the like character in 

 the Son ; it is only one out of many contributory factors. The character is 

 only a partial expression of the Father's germ-plasm; so it is with the Son's 

 character — it is not at all a full expression of his germ-plasm. Again, the Son 

 is not a product only of his Father's germ-plasm, but of his Mother's also, and 

 those of both parents in their turn are products of innumerable ancestral 

 stirps leading us back through long eons of evolution. Nor is the somatic or 

 bodily character of the Son a product only of heredity, it is the integration 

 of a number of factors acting throughout his prenatal and postnatal growths. 

 From the physicist's standpoint of causation there was no way at all to attack 

 this problem, the causes were too indefinite and elusive to be individually 

 grasped and measured. They could only be dealt with one at a time — the 

 measure of the resemblance of offspring to parent, a partial causation, led 

 Galton to the idea of correlation. 



The second problem which impressed itself on Galton's mind was that of 

 correlation in the narrow biological sense. The word itself appears to have 

 originated with Cuvier who denoted by it an association between two organs 

 or characters of a family — thus the occurrence of a split hoof with a particular 

 form of tooth, so that from the discovery of one organ a prediction could be 

 made as to the nature of others. It has been said that Cuvier 's conception 

 did not involve causation*. I do not know that any correlationist of to-day 

 would assert that the knowledge of the length of the femur, which would 

 enable him to closely predict the length of the humerus, is an assertion of 

 * See C. Herbst, Uandw'orterbuch der Naturwistseiwchaften, Bd. Ill, S. 621, Jena, 1913. 



