Moreover, one could feel nothing of the testicles in the inguinal
canal. On the other hand, the male organ was very small, but normally
developed. It was clear that this apparent hermaphrodite also was a
real male.
Another case of practical gynecomastism has been described by
Alexander von Humboldt. In a South American forest he found a solitary
settler whose wife had died in child-birth. The man had laid the
new-born child on his own breast in despair; and the continuous
stimulus of the child's sucking movements had revived the activity of
the mammary glands. It is possible that nervous suggestion had some
share in it. Similar cases have been often observed in recent years,
even among other male mammals (such as sheep and goats).
The great scientific interest of these facts is in their bearing on
the question of heredity. The stem-history of the mammarium rests
partly on its embryology (Chapter 2.24.) and partly on the facts of
comparative anatomy and physiology. As in the lower and higher mammals
(the monotremes, and most of the marsupials) the whole lactiferous
apparatus is only found in the female; and as there are traces of it
in the male only in a few younger marsupials, there can be no doubt
that these important organs were originally found only in the female
mammal, and that they were acquired by these through a special
adaptation to habits of life.
Later, these female organs were communicated to both sexes by
heredity; and they have been maintained in all persons of either sex,
although they are not physiologically active in the males. This normal
permanence of the female lactiferous organs in BOTH sexes of the
higher mammals and man is independent of any selection, and is a fine
instance of the much-disputed "inheritance of acquired characters."