When people speak of morality, does it "always" stem from a divinebeing? That may be the prevailing sentiment in certain quarters, butthere is a long and distinguished history of philosophers (many of themdevout believers) who have argued that morality couldn't derive its authority from God. Professor Gentzler has already directed you to Professor Brink'sanswer, but here is another way of looking at the problem. Consider theclaim that killing is wrong because God forbids it in the SixthCommandment. In order for God's command to create a genuine moralobligation (in this case, the obligation not to kill), God must possessa certain authority . (Otherwise anyone could issue commandsand thereby create moral obligations!) But now the question immediatelyarises: whence comes this authority? God cannot establish his authority through another command , since he must already have authorityin order for his commands to establish anything. Thus it seems thatGod's authority must come from somewhere else....

When I read your description of the situation, my first thought was that the woman has a responsibility not to protect the married man's vows , but rather to protect the married man's wife . After all, the wife is the one who is most likely to be harmed by her husband's affair, and it seems to me that we all have a responsibility not to act in ways that are likely to cause harm to others (even if we don't personally know the others in question). Of course, it is the man who bears the brunt of the responsibility in this case, since he has a specific obligation to care for his wife. Nonetheless, I do think that the woman is at least partly responsible for the negative consequences of her affair.

The theory of evolution by means of natural selection is not really a law of nature at all, at least in the sense you suggest. That is, it does not tell us anything about what we should and should not do with "the strongest seed." The theory of evolution is a descriptive theory. It informs us that the offspring of the "fittest" parents are themselves likely to have a survival or selection advantage. But the theory says nothing about how such parents should or ought to behave. No moral conclusions follow immediately from facts about natural selection. You need a second theory--a prescriptive or moral theory--to reach the conclusion that this evolutionary pattern results in a good or just outcome. And so the conflict between the laws of morality and the theory of evolution is only apparent.