MATHEMATICAL CONTRIBUTIONS TO THE THEORY OF EVOLUTION. 
109 
of the mother—a conclusion possibly warranted by our results in the case of 
daughters, but not in the case of sons. Again, why was there such a marked 
difference in eye-colour between the men and women of three or four generations 
back ? # And if it was a sexual character, why is it disappearing? Was it not, 
perhaps, a racial difference ? Light and dark eyes are not unusually associated with 
distinct races, and it is just possible that the change in eye-colour is a product of 
reproductive selection ; the old blue-eyed element of the population may be dwindling 
owing to the greater fertility of the women of dark-eyed race, and thus without any 
obvious struggle for existence and survival of the fitter, the blue-eyed race may be 
disappearing from England, as the Langobard type has so largely gone from Italy and 
the Frank from France.! It will not do to be dogmatic about these matters, but the 
more one measures characters in different generations, the less stable do races appear 
to be. We speak of the national characters of the Englishman or the Frenchman 
based upon our experience of how these races have acted in past history, but 
although there has been no great racial invasion nor struggle, can we safely assert 
the physical characters of the Englishman to-day do not differ substantially from 
those of the Englishman of the Commonwealth ? It seems to me that the possibly 
continuous change of characters in a race, not subjected to very apparent internal or 
external struggle, is a problem of the highest interest to the anthropologist and 
ultimately to the statesman. 
Whatever be the explanation of this secular change in eye-colour, it appears to 
correspond singularly enough to the secular change we have noted in the coat-colour 
of thoroughbred horses—in the older generation the sexes differ more widely than in 
the younger. 
(c.) The maternal mole relative (grandfather and uncle) is substantially lighter-eyed 
than the paternal male relative (grandfather and uncle). —I see no explanation for this 
curious result, but it seems worth while to specially note it, for there are curious 
anomalies in the inheritance through the various male and female lines which may 
find their complete explanation some day when more and possibly more trustworthy 
characters have been investigated. 
(12.) On the Variability of Eye-colour with reference to Sex and Class. —The 
determination of the relative variability of not exactly measurable characters is, as 
we have already seen (p. 105), a somewhat delicate problem. It is more so in the case 
of eye-colour in man than of coat-colour in horses, for there is greater difference in 
the means, and accordingly the ratio of o-.r/o-y, as found from the ratio of the 
“ excesses” (p. 105), will be even less reliable, j The class indices corresponding to the 
* Mr. Galton’s records went back to great-grandfathers, many of whom accordingly appear in our 
data for grandfathers. 
t See Note II. at the end of this paper. 
t The relative variability of all classes was worked out for thorough-bred horses by the “ excess ” 
method, and in only one case—that of dam and colt—did it differ from the bay range method in its 
determination of the class with the greater variability. 
