Thinking about kin

There's an interesting sounding new paper featured at the Center for Evolutionary Psychology: "The Architecture of Human Kin Detection" by Debra Lieberman, John Tooby, & Leda Cosmides:-

Humans in all known cultures feel differently about family members than they do about non-family members. To greater or lesser degrees, they are willing to sacrifice some of their own welfare to help family members, and they feel usually disgusted at the prospect of having sexual contact with nuclear family members (those who are genetic relatives). They also often feel incest to be morally wrong, and generally oppose brother-sister and parent-offspring incest in others.

What causes these phenomena, and what previously unknown facts about the human mind/brain can be discovered by using them as the basis of a research program?