102 Life and Letters of Francis Galton 



surviving editor of Biometrika, never in the first place to expect recognition 

 too quickly, and always if possible to give opportunities for publication to 

 the younger men, whose work and enthusiasm might elsewhere meet with 

 a cool reception. 



Gifted Sons of Gifted Fathers. On November 28, 1901 (Nature, Vol. lxv, 

 p. 79) Galton published a paper entitled : " On the Probability that the Son 

 of a very highly-gifted Father will be no less gifted." 



" Here we meet again with the specious objection which is likely to be adduced, as it has 

 already been urged with wearisome iteration, namely, that the sons of those intellectual giants 

 whom history records, have rarely equalled or surpassed their fathers*. In reply I will confine 

 myself to a single consideration and, ignoring what Lombroso and his school might urge in 

 explanation, will now show what would be expected if these great men were as fertile and as 

 healthy as the rest of mankind. 



" The objectors fail to appreciate the magnitude of the drop in the scale of intelligence, from 

 the position occupied by the highly exceptional father down to the level of his genetic focus (as 

 I have called it), that is the point from which his offspring deviate, some upwards, some down- 

 wards. They do not seem to understand that only those sons whoso upward deviation exceeds the 

 downward drop can attain to or surpass the paternal level of intelligence, and how rare these 

 wide deviations must be." 



Galton points out that besides the exceptional quality of the father there 

 are three other factors influencing the position of the offspring's genetic focus : 

 (i) the quality of the mother, (ii) the quality of the father's ancestry and 

 (iii) that of the maternal ancestry. The problem is — if we do not discuss it 

 from an individual case — what weight to give to these three additional factors. 

 Now it is a well-recognised fact that while exceptional parents produce 

 exceptional sons at a much higher rate than non-exceptional parents do, the 

 pairs of the latter are so much more numerous than those of the former that 

 it is far more probable that an exceptional man is the son of non-exceptional 

 than of exceptional parents. Hence when we are dealing with average results 

 (ii) and (iii) will not be highly contributory. On the other hand many ex- 

 ceptional men have wives much above the average, and we ought to reckon 

 something for the influence of the mother. Let us take her influence to be 

 measured by an exceptionality one-fifth that of her husband and suppose him 

 to be one man in a thousand f. If we have somewhat over-estimated the 

 average exceptionality of the wife, as one woman in two hundred, we have done 

 so purposely partly to account for possibly neglected paternal and maternal 

 ancestry, and partly to give the son a better chance of reaching to his father's 

 exceptionality. On these assumptions we may treat the problem on rather 

 more modern lines than Galton has done. The "genetic centre" or mean of 

 the array of offspring of our exceptional man and his wife will be at a 

 distance 2*086 x <r, where cr is the standard deviation or variability of 

 the population for the given character. This supposes the parental corre- 

 lations to be equal and of intensity '46, and the coefficient of assortative 

 mating to be '25, both reasonable average values. The average son of our 



* See what has already been said regarding this point on our p. 27 above. 

 t Assuming that the coefficient of assortative mating to be - 25 then the average wife of an 

 exceptional husband (1 in 1000) would only be 1 in 40. 



