Whether or not same-sex families attain the legal right, as opposite-sex couples now have, to solemnize their relationship in civil marriage, the two family forms will continue to have fundamentally different, even contrasting, effects on the biological component of child well-being, to the relative detriment of children in same-sex families.

Functionally, opposite-sex marriage is a social practice that, as much as possible, ensures to children the joint care of both biological parents, with the attendant benefits that brings; same-sex marriage ensures the opposite…