If the mother is legally married the husband is assumed to be the father of the baby in many states and Washington DC. The husband's presence is not required to list his name on the birth certificate because the legal marriage automatically makes the husband the legal father. In washington state if you are not married and the father of the baby wants to be listed on the birth certificate you need to have both parents sign a form in the presence of a notary. Birth certificates can be changed in the case of mistaken paternity. If the mother is married and her lover is the genetic father of the baby it is possible that the husband can legally block the lover from having any contact with the child. Legally that child is his, and genetics doesn't matter. I have seen it happen where the father finds out about the affair, divorces wife, and then WINS CUSTODY of all the children.

You do not need to be the genetic father of the children in a relationship to be legally required to pay child support. If you raised the kids with your wife and found out the kids were not yours in a later divorce, the fact that you legally were their parent still obligates you to pay support. I know this is the case in washington.

These laws were written before we knew about genetics and DNA, and before sperm donors, egg donors, and surrogates came about. I suspect laws will change with time to accommodate genetic parents and give them more legal rights. We may end up with more than two legal parents of a child being possible.