In the animal world, most males are like many country song guys -- they love 'em and leave 'em. From a genetic point of view, they increase their chances of spreading their genes by mating with as many females as possible.
One of the fewer than 5% of mammals that stick with one mate is the prairie vole. Once this guy finds a mate, he helps raise the kids, fights off potential suitors, and sticks with her for life. His close relative, the meadow vole, is a different story. He is more typical in that he mates with as many females as possible and pays no attention to the kids.
So what's the difference between these two kinds of voles? Careful examination showed that the prairie vole had a lot more of a protein called the vasopressin receptor in its brain than did the meadow vole. To test whether this was the reason for the difference in behavior, scientists used gene therapy to add extra receptors to the brain of the meadow vole.
The result? Now the meadow vole is more like his cousin -- he sticks with one mate even when others are freely available. It is astonishing that a single gene could have such a huge impact on such a complex behavior.
We don't know whether this applies to humans but we do know that the same pattern exists with monkeys. Monkeys who like to fool around have fewer vasopressin receptors than do more faithful monkeys.
So can we turn those country song guys into more stay at home types? We certainly can't yet do gene therapy on humans like was done in this study. But maybe some sort of drug that works on the vasopressin receptor could be made to turn cheating men into prairie voles.
Of course, even if the vasopressin receptor is important in human monogamy and we come up with some way to tweak it to keep men from cheating, should we? Besides ethical concerns, we'd lose an awful lot of good country music...