Why do so many people stay in monogamous relationships and take care of kids rather than fool around like wild chimpanzees? Are family values etched into our DNA through eons of evolution? Or imposed by the strictures of culture, law and religion?
I thought a good place to look for answers would be the annual meeting of the American Association of Physical Anthropologists, when hundreds of researchers recently converged in Philadelphia to compare notes.
One way anthropologists try to understand our species is to study us in the context of other primates. Our closest genetic relatives, the chimps, mate promiscuously and leave all child care to the females, but we have slightly more distant cousins that practice family values even Pat Robertson would admire.
Where things get really interesting is in the study of male animals, says Penn anthropologist Eduardo Fernandez-Duque, who chaired a session on paternal care. Female mammals tend to bond with their babies, whatever the mating system, but in males, parental care is connected with monogamy and varies wildly across species.
He works in South America where he studies the uncommonly monogamous and fatherly titi monkeys. When a baby monkey is born, it almost immediately latches onto the father, who dutifully ferries it around more often than the mother.
Usually, the most monogamous monkey species make the most devoted fathers, say anthropologists, because the males stand a better chance of caring for their genetic offspring and not someone else's.
But there are some surprising exceptions.
Baboon females tend to mate with multiple males, yet when babies are born, males come sniffing around.
They pick up certain babies they may deem likely to be their own and start carrying them around, says Duke University anthropologist Susan Alberts.
How can they sense which babies are theirs? "My working hypothesis is males have several potential cues - none of which is very accurate - but they combine them," she says. Maybe pheromones and the memory of mating with a female during her fertile period help.
One difference between bonding animals and loners is the distribution of receptors in the brain for the hormones oxytocin and vasopressin, both associated with falling in love.
For us humans, biology as well as culture drives men and women to fall in love and work together to raise children.
Other anthropologists at the meeting approach the nature/culture questions by living with people from the few pockets of cultural diversity untouched by American Idol or Burger King.
Frank Marlowe of Florida State University spends months living among the Hadza, a foraging group in Tanzania. Hadza men gather honey and hunt for all sorts of animals from giraffes on down. They also help with the kids. "It's funny that some claim the nuclear family is a Western invention," says Marlowe, when it's common around the world.
What he and other researchers are hotly debating is how devoted indigenous men are to their families, focusing on why they spend so much time hunting animals.
"Are men hunting to provision their kids or is it just a way of showing off to others what a bad-ass you are?" asks Michael Gurven, an anthropologist who studies the Tsimane of Bolivia.
The 8,000 remaining Tsimane still depend on hunting and gathering. The men kill wild pigs, monkeys and tapirs. Gurven found the men did try hard to help their families. A reputation as a bad-ass hunter, he says, is a nice fringe benefit.
That's the same conclusion Marlowe drew about the Hadza. What the men really wanted was to provision their families. Showing off was a lower priority.
Most people today hunt for money instead of meat, but we're still trying to balance this with child-care duties. For his part, Penn's Fernandez-Duque said he'd like to see more research on the relative benefits of working vs. child care for American men. What balance benefits the family most?
He said he'd do some of that research himself if he weren't so busy. He and his wife, also a professor, are raising three sons.
or Not." Next week.