Is sex socially constructed?

I had this really great conversation, one that definitely qualifies as one of the best I have had in a while, with my independent studies professor the other day. He's in the philosophy department, but focuses on religious studies, so we can talk for hours. My semester research topic was how the christian evangelical world is relating to postmodern philosophy and culture, but I learned much less from researching the paper than from the stimulating discussions we had throughout the semester. It really is amazing that two people can discuss issues of faith and religion and reality and not agree on all issues, but nevertheless walk away stimulated and not angry. It can happen, but not if someone has the attitude that they have the monopoly on truth and can't learn from someone that doesn't have the same perspective as we have. Nevertheless, here's a question he challenged me with, "is sex socially constructed?" Before you gasp in disbelief and tell me that our view of proper sexual relations is "biblical" (ahh, the trump card)- think about this: Abraham, David and Solomon had multiple wives and it is never spoken of as sinful for them. Flashing forward to the New Testament, Paul believed people should be single because Jesus was coming soon. Do we really view sex like solomon or Paul?... I leave you with that