Which came first: the Chicken or the Morality?

The original article by Steven Pinker sounds kinda long and heavy. The summation at What Silence isn't exactly brief, either. It's a good read, but here's my favorite part:

...Consider [this situation], originally devised by the psychologist Jonathan Haidt:

Julie is traveling in France on summer vacation from college with her brother Mark. One night they decide that it would be interesting and fun if they tried making love. Julie was already taking birth-control pills, but Mark uses a condom, too, just to be safe. They both enjoy the sex but decide not to do it again. They keep the night as a special secret, which makes them feel closer to each other. What do you think about that — was it O.K. for them to make love?

Most people immediately declare that these acts are wrong and then grope to justify why they are wrong. It's not so easy. In the case of Julie and Mark, people raise the possibility of children with birth defects, but they are reminded that the couple were diligent about contraception . They suggest that the siblings will be emotionally hurt, but the story makes it clear that they weren't. They submit that the act would offend the community, but then recall that it was kept a secret. Eventually many people admit, "I don't know, I can't explain it, I just know it's wrong." People don't generally engage in moral reasoning, Haidt argues, but moral rationalization: they begin with the conclusion, coughed up by an unconscious emotion, and then work backward to a plausible justification.