[Kozak]

The logic of biology. One man + one woman = a reproductive unit. Thats the natural minimum that would suggest a basic "family unit".

[BikerNYC]

I understand. But why does that family unit have to be married, with a license, with or without a church? Face it, the reason marriage is the way it is now is because of public policy, not logic. We simply prefer things this way. Moreover, how many children now are born out of wedlock? How many adults are actually married? These figures show that this "logic" you speak of is not air tight.