25, the objection
becomes less formidable. Certainly it will hardly be argued that one of
the partners infects the other with this disability.
As a fact, a correlation of .25 between husband and wife, for
tuberculosis, is only partly due to infection. What it does mean is that
like tends to mate with like--called assortative mating. This
coefficient of resemblance between husband and wife in regard to
phthisis is about the same as the correlation of resemblance between
husband and wife for eye color, stature, longevity, general health,
truthfulness, tone of voice, and many other characters. No one will
suppose that life partners "infect" each other in these respects.
Certainly no one will claim that a man deliberately selects a wife on
the basis of resemblance to himself in these points; but he most
certainly does so to some extent unconsciously, as will be described at
greater length in Chapter XI. Assortative mating is a well-established
fact, and there is every reason to believe that much of the resemblance
between husband and wife as regards tuberculosis is due to this fact,
and not to infection.[59]
Again, it is objected that the infection of children is not a family
matter, but due to tuberculous cows' milk: how then does it appear
equally among the Japanese, where cows are not tuberculous and cow's
milk rarely used as an infant food: or among such people as the
Esquimaux and Polynesians, who have never seen a cow?
But, it is argued, at any rate bad housing and unsanitary conditions of
life will make infection easier and lower the resistance of the
individual.
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