If monogamy were against nature or human nature specifically, no human could do it, the way fish cannot live out of their element. But the existence of faithful couples does demonstrate monogamy as a human possibility permitted by nature. On the other hand, the existence of non-faithful spouses shows that betrayal also is permitted by nature. In conclusion, nature is neither for or against either monogamy or betrayal when permission to act is involved. However, nature does permit numerous things that injure. The final question comes down to injury: even if nature lets someone hurt him/herself, is the injury a good just because nature lets one do it?