Steven Johnson: We have one of the longest childhoods of any creature. He says evolution has given us an inclination to have special relationships in our life that are often like my genetically related sister or brother. The key difference between a friend and a family relationship is contingency, he says. "I would truly ultimately reject anything where I can't come up with non-contingency"
If you’re frustrated with your family, should you cut ties with them? Who’s more likely to break with relatives over politics, liberals or conservatives? And what would it take for Stephen to buy a baby elephant?