pigment in the body that arises from that germ-plasm. The absence of iris pigment is proof of the absence of the pigment determiner from the germ-plasm. If both parents lakc brown pigment, their offspring, being devoid of the determiner for brown pigment, will all lack brown pigment. As a matter of experience two parents both with blue eyes will have only blue-eyed offspring. Similarly, if the hair of the parents be flaxen, that is evidence of the absence of a hair-pigment determiner in their germ-plasm. In the united germ-plasms of two flaxen-haired parents there is no determiner for hair pigment and all children will have flaxen hair. This agrees, again, with experience. For the same reason parents both lacking curliness or waviness of hair will typically have only straight-haired children.
Hair and eye color are characteristics which serve well to illustrate the precision of the modern science of heredity, but they are ordinarily considered to be immaterial to well-being. But if it is true, as Major C. E. Woodruff maintains, that pigmentation protects individuals from the
Fit and Unfit Matings
injurious effects of the tropical sun's rays then one may say that the marriage of two blue-eyed persons in the tropics would be an unfit marriage. On the other hand, the marriage of a blond with a brunet would be fit, for the darker consort would bring into the combination the determiner for pigment and ensure a dark progeny. In the tropics, then, the marriage of light with dark or of two dark persons is, by hypothesis, a fit mating while that of two blonds is unfit.
We may now extend the study of the method of inheritance to cases of abnormalities and diseases, and we shall see that just as it is hard to draw the line between these two sorts of characteristics so they show no difference in their general method of inheritance.
A typical example of an abnormality is that of brachydactyly or short-fingeredness, a condition in which each digit comprises only two phalanges - the fingers are all thumbs. This result seems to be due to an inhibition of the normal growth process. An abnormal person married even to a normal will beget 100 percent