[dragonwriter]

In its historical roots, though often (but far from always) without the "orphan" part, that's exactly what marriage is: the process by which a family chooses some non-family person to share with some member of the family in the inheritance of the family. (Sometimes in a reciprocal, but even when so often not symmetrical, relationship with another family.)

[alexro]

Usually in such a way that when the parents get older their children would care of them, isn't it?