“We are now approaching a social revolution, in which the old economic foundations of monogamy will disappear just as surely as those of its complement, prostitution. Monogamy arose through the concentration of considerable wealth in one hand — a man's hand — and from the endeavor to bequeath this wealth to the children of this man to the exclusion of all others. This necessitated monogamy on the woman's, but not on the man's part. Hence this monogamy of women in no way hindered open or secret polygamy of men. Now, the impending social revolution will reduce this whole care of inheritance to a minimum by changing at least the overwhelming part of permanent and inheritable wealth—the means of production—into social property. Since monogamy was caused by economic conditions, will it disappear when these causes are abolished?
One might reply, not without reason: not only will it not disappear, but it will rather be perfectly realized. For with the transformation of the means of production into collective property, wagelabor will also disappear, and with it the proletariat and the necessity for a certain, statistically ascertainable number of women to surrender for money. Prostitution disappears and monogamy, instead of going out of existence, at last becomes a reality—for men also.
At all events, the situation will be very much changed for men. But also that of women, and of all women, will be considerably altered. With the transformation of the means of production into collective property the monogamous family ceases to be the economic unit of society. The private household changes to a social industry. The care and education of children become? a public matter. Society cares equally well for all children, legal or illegal. This removes the care about the "consequences" which now forms the essential social factor—moral and economic—hindering a girl to surrender unconditionally to the beloved man. Will not this be sufficient cause for a gradual rise of a more unconventional intercourse of the sexes and a more lenient public opinion regarding virgin honor and female shame? And finally, did we not see that in the modern world monogamy and prostitution, though antitheses, are inseparable and poles of the same social condition? Can prostitution disappear without engulfing at the same time monogamy?”

The Origin of the Family, Private Property and the State (1804) as translated by Ernest Untermann (1902); Full English text of The Origin of the Family, Private Property and the State http://www.marxists.org/archive/marx/works/1884/origin-family/index.htm - Full original-language German text of The Origin of the Family, Private Property and the State http://www.mlwerke.de/me/me21/me21_025.htm