Dynasties and aristocracies which have disregarded the laws of nature have decreased in numbers and degenerated in stature; 'mariages de convenance' leave their enfeebling stamp on the offspring of them (King Lear).

The marriage of near relations, or the marrying in and in of the same family tends constantly to weakness or idiocy in the children, sometimes assuming the form as they grow older of passionate licentiousness.

The common prostitute rarely has any offspring.

By such unmistakable evidence is the authority of morality asserted in the relations of the sexes: and so many more elements enter into this 'mystery' than are dreamed of by Plato and some other philosophers.
Recent enquirers have indeed arrived at the conclusion that among primitive tribes there existed a community of wives as of property, and that the captive taken by the spear was the only wife or slave whom any man was permitted to call his own.

The partial existence of such customs among some of the lower races of man, and the survival of peculiar ceremonies in the marriages of some civilized nations, are thought to furnish a proof of similar institutions having been once universal.
There can be no question that the study of anthropology has considerably changed our views respecting the first appearance of man upon the earth.
We know more about the aborigines of the world than formerly, but our increasing knowledge shows above all things how little we know.