In a post about the recent finding that first-cousin marriage carries a lower risk of genetic defect than previously thought, Charles Murtaugh says:

...although we consider it tragic that a Huntington's patient might have affected children, we aren't repulsed at the very idea of allowing him or her to reproduce. This suggests that our repugnance at brother-sister incest (which carries a much lower than 50% risk of Huntington's-level disease) has little if anything to do with genetics. Score one for Leon Kass's "wisdom of repugnance" thesis.

I don't think so. An evolutionary-psychology explanation for such repugnance (and in fact, all repugnance--after all, repugnance is an emotion, and emotions are just our genes' way of getting us to do what they want) is that it evolved precisely as a result of the evolutionary benefit of not getting it on with your siblings.

But not all evolutionary adaptations are advantageous in the modern world. What repulsed us on the savanna is not necessarily something to be feared, or disgusted by, in the twenty-first century. Repugnance is like any other feeling--consider it a suggestion, rather than a mandate. Repugnance, by itself, cannot provide an infallible basis for laws, particularly when it's not universal.

I share most people's repugnance about incest--I feel none about cloning, regardless of what Professor Kass thinks (or, to be more accurate, feels). Unlike him, I can distinguish between blind evolutionary urges, and true wisdom, which is a much more recent human development.