Two things I know about human mating:
1. Having sex with someone releases a flood of hormones in the brain that make you feel attached to that person. Helen Fisher puts it well: “The bottom line is, if you don’t want to get attached to somebody, it’s easier to not sleep with them . . . Because you might end up being attached to somebody who really does not fit into your life.”
2. Human males have genes that code for a particular kind of vasopressin receptor in the brain. Studies done in prairie voles–which have the same gene–have found that the voles with longer vasopressin genes show greater monogamy and spend more time caring for their pups. They’re also less likely to mate with other females.
Dr. Louann Brizendine puts it well: “The human gene comes in at least seventeen lengths. So the current joke among women scientists is that we should care more about the length of the vasopressin gene in our mates than about the length of anything else. Maybe someday there will be a drugstore test kit–similar to a pregnancy test–for how long this gene is so you can be sure you’re getting the best guy before you commit.” (p. 73-74).