The ability to spoon down ice cream or chug a milkshake might not seem like an evolutionary advantage in our weight-conscious society. But scientists say that 5,000 to 10,000 years ago, around the time dairy farming began in Northern Europe, natural selection encouraged the spread of a genetic mutation that enabled adults to digest the sugars in milk. Those with the new gene-lactase-had a nutritional advantage over those who lacked it, so they proliferated, along with the mutation.

What´s left of the General Tso´s chicken is on the coffee table. The sauce that eluded my mouth is congealing on my T-shirt. American Idol just started. And Megan, my fiance of three days, is getting ready to swab the inside of my mouth with Q-Tips that are nearly as long as chopsticks. â€OK, open that mouth,†she says. â€Wider.†She is a doctor. I do as I´m told. â€You know, these look like little Pap-smear brushes,†she muses. My mouth snaps closed. â€C´mon, open up,†she says. I stall.