Within recent years the theory has prevailed among certain
sociologists that positive masculinity is stronger in the offspring of
consanguineous marriages than in the offspring of unrelated parents.
Professor William I. Thomas in his writings and lectures asserts this
as highly probable.[28] Westermarck,[29] to whom Professor Thomas
refers, quotes authorities to show that certain self-fertilized plants
tend to produce male flowers, and that the mating of horses of the
same coat color tends to produce an excess of males.[30]

[Footnote 28: _Sex and Society_, p. 12.]

[Footnote 29: _History of Human Marriage_, p. 476.]

[Footnote 30: _Goehlert, Ueber die Vererbung der Haarfarben bei den
Pferden._ Quoted by Westermarck, p. 476.]

Westermarck continues, quoting from Düsing:[31] "Among the Jews, many
of whom marry cousins, there is a remarkable excess of male births. In
country districts, where, as we have seen, comparatively more boys are
born than in towns, marriage more frequently takes place between
kinsfolk. It is for a similar reason that illegitimate unions show a
tendency to produce female births."

[Footnote 31: _Die Regulierung des Geschlechtsverhaeltnisses_, pp.
243-244.]

Westermarck comments: "The evidence for the correctness of his
deduction is, then, exceedingly scanty--if, indeed it can be called
evidence. Nevertheless, I think his main conclusion holds good.