334 Life and Letters of Francis Galton 



generally of the same generation and approximate age ; the uncle and nephew belong to different 

 generations and may be of considerably different ages. But if anything the avuncular correla- 

 tion is less than the cousinal, and accordingly I am not sure that the age and environmental 

 differences would do more than equalise their values. Again we should expect brothers to he 

 more alike than parent and offspring, but the fraternal correlation is only very slightly greater 

 than the parental, and this again is due possibly to the age and nurture influences being more 

 effective in the latter case*. As an illustration of what might happen, let us adopt as hypothesis 

 an alternative inheritance in which | the offspring follow one parent and | the other. In this 

 case 50 °/ o of the offspring are like a given parent, but only 33^ °/ o of the brothers are like a 

 given brother. Thus the parent has greater resemblance to his offspring than the brother to his 

 brethren. Now let us look at the grandchildren of a pair, A and B, on the assumption of this 

 alternate inheritance : 



A = B 



A l = C, A s = Z>, B, = E 1 



B^l\ 



I I I 'I I I I I 1 I I J 



A 3 A i t C t A b A 6 A D 3 B 3 B t E, E 3 



\ l_. 



-S 5 B« K Fs 



With regard to the original grandparents, the 16 grandchildren are either like one or other 

 of them, A or B, or unlike them, taking after their daughters or sons-in-law, C lt D lt E lt or F 1 . 

 Thus 25 °/ o of the grandchildren are like a given grandparent. Now consider an A 1 uncle, he 

 has 12 nephews or nieces and 2 of these are like him, i.e. 16-6 "/„• Each individual cousin like 

 A 3 has two out of 12 cousins like himself, again 16 - 6 °/ o . It would thus appear that on such a 

 theory we should have as great a resemblance between cousins as between uncle and nephew. 

 Now I don't suggest that this scheme is actually at all representative of what takes place, but 

 it seems to me to indicate that we can invent schemes in which it does not follow that uncle 

 and nephew have a greater measure of resemblance than cousin and cousin, nor brother and 

 brother a greater measure than parent and offspring. We must first observe and obtain our 

 correlations and then endeavour to interpret them. Affectionately, K. P. 



The divergence of view between Francis Galton and myself with regard 

 to the use of technical terms is well illustrated in the following letter. I had 

 sent him a paper in proof which was shortly to appear in Biometrika. Of 

 this he wrote : 



Quedley, Haslemere. March 8, 1908. 



My dear Karl Pearson, I would strongly urge a footnote to the first page J headed — 

 " Technical words used," including Chromomeres, Chromosomes, Determinants, Mytosis, also even 

 Cytology, Somatic and Zygote, with definitions of each. Allogene might be dismissed with the 

 remark " explained in text." Thinking of the men who ought to read the memoir with interest, 

 — Yule, MacMahon, G. Darwin, Burberry, etc., — there is hardly one who would know the 

 meaning of these words, or would care to read the memoir unless they were first defined. This 

 or some analogous plan would often be a great lielp to readers of Biometrika articles. It is 

 a most interesting investigation of yours. I had long had a vague idea that something of the 

 sort was needed, but could not phrase it satisfactorily to myself. You must indeed feel the void 

 left by Weldon. 



* Galton's argument was that in the case of cousins (sons of two brothers) there were two 

 wives, the cousins' mothers producing variability, whereas in the case of uncle and nephew there 

 was only one mother, the sister-in-law of the uncle, to be considered. So in the case of two 

 brothers, we might argue there is no source of difference in descent, but in father and son the 

 mother comes in as a cause of additional variability. 



t This refers to the proofs of a memoir " On a Mathematical Theory of Detcrminantal 

 Inheritance from Suggestions and Notes of the late W. F. R. Weldon," ultimately published 

 in Biometrika, Vol. vi, pp. 80-93. 



