34 Life and Letters of Francis Galton 



scientific basis by suggesting that the hereditary honour should follow ability 

 in the stock and not be granted to a preordained individual. 



D. Attempt to demonstrate the Law of Ancestral Heredity on Eye- 

 Colour. In 1886 Galton published in the Proceedings* of the Royal Society 

 a paper on "Family Likeness in Eye-Colour." The only earlier paper I know 

 which deals with this topic is that by Alphonse de Candollef. That paper has 

 no adequate statistical treatment, and suffers from two fundamental errors. 

 The material was collected not only from Switzerland with its mixed races, 

 but from Sweden, Germany and France, so that beyond the immediate 

 parents, there must have been great differences in the eye-colours of the 

 unrecorded earlier ancestry, and secondly the contributors were especially 

 requested to leave out offspring of "doubtful" eye-colour, and also those of 

 definite eye-colour whose parents had doubtful eye-colour. I do not think that 

 in de Candolle's paper any results of real scientific value are reached. Galton's 

 method of approaching the problem is entirely different. He starts from his 

 Law of Ancestral Heredity, and endeavours to apply it to eye-colour, which 

 he says does not usually blend. Accordingly he proportions the ancestral 

 contributions not in the character of the individual but among the whole 

 group of offspring. As Galton believed he had deduced from his mid- 

 parental regression of f the system i + i + £+--- for contributions to the 

 individual character in the case of stature, so he now supposes that an indi- 

 vidual parent's eye-colour will determine on the average that of \ of the 

 offspring, that of a grandparent -j^ of the offspring, and so on. 



"Stature and eye-colour are not only different as qualities, but they are more contrasted in 

 hereditary behaviour than perhaps any other simple qualities. Speaking broadly parents of dif- 

 ferent statures transmit a blended heritage to their children, but parents of different eye-colours 

 transmit an alternative heritage. If one parent is as much taller than the average of his or her 

 sex as the other parent is shorter, the statures of their children will be distributed in much the 

 same way as those of parents who were both of medium height. But if one parent has a light 

 eye-colour and the other a dark eye-colour, the children will be partly light and partly dark, and 

 not medium eye-coloured like the children of medium eye-coloured parents. The blending of 

 stature is due to its being the aggregate of the quasi-independent inheritances of many separate 

 parts, while eye-colour appears to be much less various in its origin. If then it can be shown, as 

 I shall be able to do, that notwithstanding this two-fold difference between the qualities of 

 stature and eye-colour, the shares of hereditary contribution from the various ancestors are in 

 each case alike, we may with some confidence expect that the law by which these hereditary 

 contributions are governed will be widely, and perhaps universally applicable J." 



Galton starts his paper by considering whether there has been a secular 

 change in eye-colour in the four generations to which his Records of Family 

 Faculties extended. He started with those who ranked as "children" in the 

 pedigree as Generation I ; their parents, uncles and aunts were Generation II ; 

 the grandparents and their collaterals were Generation III, while the great 

 grandparents and their collaterals were Generation IV. He gives the 



* Vol. xl, pp. 402-416. Read May 27, 1886. 



t "Her^dite de la couleur des yeux dans l'espece humaine." Archives des Sciences physiques 

 et naturelles, 3 Rme Periode, T. xn, pp. 97-120, Geneva, 1884. 

 X Hoy. Soc. Proc. pp. 402-3. 



