112 
PROFESSOR K. PEARSON AND DR. A. LEE ON 
who have female B s is invariably greater than the variability of all the A’s who 
have male B’s. 
The law appears to be universal, at least it is absolutely true for all the 10 cases to 
which we can apply it. Thus the father of sons is less variable than the father of 
daughters, the maternal grandmother of grandsons less variable than the maternal 
grandmother of granddaughters, or the paternal uncle of nephews less variable than 
the paternal uncle of nieces. In other words, although women appear, in eye-colour, 
to be less variable than men, they spring from more variable stocks. 
This law is a remarkable one, but in face of the evidence for it, it seems difficult to 
doubt its validity. Should it be true for more characters in man than eye-colour, # 
the conclusions to be drawn from it will be somewhat far-reaching, however difficult 
it may be to interpret its jffiysiological significance. 
(c.) On the Relative Variability of Different Generations .-—We have already had 
occasion to refer to the general rule that the older generation will be found less 
variable than the younger, for it is in itself a selection, namely, of those able to 
survive and reproduce themselves. But this rule is obscured in the present case by 
several extraneous factors, thus :— 
(i.) The male is sensibly more variable than the female, consequently it is quite 
possible that an elder male generation should appear more variable than a younger 
female generation. 
(ii.) There appears to be a secular change in eye-colour going on. Thus while the 
grandparental population is a selection from the general population, the general 
population, at a given time, is a selection from that of an earlier period. 
Thus, taking means in the cases of the grandparental and avuncular relationships, 
we have from (y) the following results :— 
The father is more variable than son and than daughter. 
The mother is less variable than son and more than daughter. 
The grandfather is more variable than grandson and than granddaughter. 
The grandmother is less variable than grandson and more than granddaughter. 
The uncle is more variable than nephew and more than niece. 
The aunt is less variable than nephew and more than niece. 
In other words, the older generation is always more variable than the younger, 
except when rule (a), that the male is more variable than the female, comes in to 
overturn this law. If we confine ourselves to comparisons of the same sex the rule is 
seen to be universal. 
We are thus forced again to ask for an explanation of the decreasing variability of 
eye-colour, and can only seek it in that secular change we have several times had 
* Fathers of daughters are more variable in stature than fathers of sons (‘ Phil. Trans./ A, vol. 187, 
p. 27t). I propose to reinvestigate the cptestion with regard to mothers from the material of my family 
measurement cards, which is far more extensive than the material I had at my disposal in 1895. 
