Why does the Manifesto say that the family is absent among the proletariat?
Here is the full quote: "Abolition [Aufhebung] of the family! Even the most radical flare up at this infamous proposal of the Communists. On what foundation is the present family, the bourgeois family, based? On capital, on private gain. In its completely developed form, this family exists only among the bourgeoisie. But this state of things finds its complement in the practical absence of the family among the proletarians, and in public prostitution. The bourgeois family will vanish as a matter of course when its complement vanishes, and both will vanish with the vanishing of capital."
I understand how the bourgeois family is based on private gain, with family capital, inheritance and so on. But I don't understand how the family itself is absent among the proletarians.