60 Life and Letters of Francis Galton 



p. 185), that is of the continuity of the germ-plasm. It is only in a figurative 

 sense that we can look upon the inheritance of the individual as a mosaic, and 

 speak of the contribution of an ancestor to the result. The individual is the 

 product of the germ-plasms that go to his production, not of the individual 

 ancestors. The study of the characters of the individual ancestors is only 

 ancillary to a study of the possibilities of those germ-plasms. The correlation 

 of a somatic character in a great grandparent, say, and great grandchild is 

 not in any sense a real measure of what the former contributes to the 

 latter, nor is the corresponding multiple regression coefficient such a measure. 

 We are testing what on the average we can predict of the somatic characters 

 of the offspring from a knowledge of what the germ-plasms of the " stirp " 

 have produced in the past. In other words the term " contribution of an 

 ancestor" should be interpreted as, or be replaced by, "contribution of the 

 ancestor to the prediction formula." It is in no sense a physical contribution 

 to the go^m-plasms on which the somatic characters of the offspring depend. 

 I do not think that anyone acquainted with the theory of multiple correlation 

 would interpret the Law of Ancestral Heredity in any other sense ; but 

 Galton's use of the terms " particulate inheritance," " mosaic," " heritage 

 from distant progenitors," must be admitted to be easily capable of mis- 

 interpretation. 



Galton then deals with the " heritages that blend and those that are 

 mutually exclusive," citing as an illustration of the former, skin-colour in 

 crosses between white and negro, and of the latter eye-colour. He does not 

 here, any more than in his fundamental paper on eye-colour (see our p. 34), 

 explain for what reason he assumes the distribution of eye-colour in the 

 array of offspring due to a definite ancestry will be in the same proportions 

 as in the case of a blended character in an individual offspring. Galton con- 

 cludes that : 



"There are probably no heritages that perfectly blend, or that absolutely exclude one another, 

 but all heritages have a tendency in one or the other direction, and the tendency is often a very 

 strong one — A peculiar interest attaches itself to mutually exclusive heritages, owing to the 

 aid they must afford to the establishment of incipient races." (pp. 13-14.) 



So far, however, as the struggle for existence and evolution are concerned, 

 this last sentence must mean that a mosaic of the characters of two distinct 

 races is for some environmental reasons more fitting than either pure race, 

 and what is more, that the characters in the new mixed race will be stable 

 and not segregate out again. 



In the concluding paragraph we read : 



"The incalculable number of petty accidents that concur to produce variability among 

 brothers, makes it impossible to predict the exact qualities of any individual from hereditary 

 data. But we may predict average results with great certainty, as will be seen further on, and 

 we can also obtain precise information concerning the penumbra of uncertainty that attaches 

 itself to single predictions. It would be premature to speak further of this at present; what 

 has been said is euougli to give a clue to the chief motive of this chapter. Its intention has been 

 to show the large part that is always played by chance in the course of hereditary transmission, 

 and to establish the importance of an intelligent use of the laws of chance and of the statistical 

 methods that are based upon them, in expressing the conditions under which heredity acts." 

 (pp. 16-17.) 



