Evolutionarily, women bond to nurture and men bond to protect. The hormone that activates the protect-and-guard impulse (the bonding impulse) in men is called vasopressin. A variant in a gene called RS3 AVPRIA reduces men’s receptivity to vasopressin. According to a Swedish study, the married men with this gene variation were likelier to have experienced a marital crisis in the past year, likelier to have talked about divorce than those without the variant. They were also likelier, overall, to be unmarried. "If you want a guy that’s bonded to you tightly, you want to make sure you’ve got a guy with the right variance," says Alexander in a phone call.
In the last chapter of the book, the authors imagine a world in which online personals contain genetic information as well as physical details and professional status. "In addition to bundling the familiar 'tall, professional, SWM' in personal ads, why wouldn’t men proclaim 'AVPRIA RS3 neg.' as yet another selling point? Men and women routinely demand body types in their personals. Why not toss in genetic types?"