There is such diversity in human biology that it has thus far been impossible to find one infallible definition of "male" or "female" - so the whole idea of limiting marriage based on "one of each" is a fallacy in itself. XY Male and XX female may be the two dominant sexes, but there are more than 27 intersex conditions that can make one's sex indeterminant. Intersex conditions are as common as 1 in 2000 births. What about all those folks? Just move on. Marriage is a legal contract between two people. It actually started as a contract between a man and the bride's father. It has nothing to do with religion. So get your nose out of other people's genitals and get on with your life.