36

Life and Letters of Francis Galton

percentage values on considerable numbers in the groups combined of Light and Dark Blue, Grey, Blue Green

It will be seen that, while there is no significant change in the percentage of light eyes in the women, there is really such a change in the light eyes of the men ; the grandparental and great grandparental generations have more bluish eyes. Were it not for the fact that there is no change in the women, we might attribute this not to a racial change going on, but to men's eyes growing lighter with extreme age. I have no statistical data to produce, but my impression of the marked frequency of very light colour in old men's eyes is strong. At the same time I know no physiological reason why men's and not women's eyes should grow lighter with greater age.

On the basis of his diagrams Galton considers that he may disregard "a current popular belief in the existence of a gradual darkening of the population, and can treat the eye-colours of those classes of the English race who have contributed to the records, as statistically persistent during the period under discussion" (p. 406).

Galton next states that he considers that there are only two fundamental types of eye-colour, the light and the dark, but under this supposition the medium tints are troublesome. Such tints be has classified under " Dark Grey and Hazel." In these cases the outer portion of the iris is usually of a dark grey colour, and the inner of a hazel. The proportions of grey and hazel vary, and the eye is called " dark grey" or "hazel" according to the colour which happens most to arrest the attention of the observer. Galton's attempt to deal with these medium eyes, of which there are in the population about 12.7 °/o, is to me unconvincing ; yet the fact that he recognises their existence is more satisfactory than the Mendelian treatment which disregards them entirely !

Galton for conciseness terms all these eyes "hazel." He defines a hazeleyed family to be one in which there is at least one hazel-eyed child, and he proceeds to inquire into the constitution and ancestry of such "hazel-eyed" families or sibships. He obtains the results tabulated on p. 37.

Now it is clear from the table that when there is a hazel-eyed child in a sibship, the percentage of dark eyes in the sibship is only very slightly reduced, but the number of light-eyed brothers and sisters is 16 °/o below that of the general population. Again in the parental generation, there are 12 °/ fewer light-eyed parents of hazel-eyed parents, and this 12 °/. is transferred to the hazel-eyed group, the dark-eyed parents remaining at