The landmark study by University of Texas sociology professor Norval Glenn and Elizabeth Marquardt, "Hooking Up, Hanging Out and Hoping For Mr. Right", reported that women in modern America are given the choice of two extreme models of romantic heterosexual relationships: "hooking up'" or being "joined at the hip."The hook up, practiced by 40 percent of women in the study, is "friends with benefits," meaning casual sex without commitment. The other common relationship is "joined at the hip," where a couple that doesn't know each other very well commits to a sexual relationship and spends all their time together.
Author Dannah Gresh notes that the "hook up culture" is no free lunch:
"What happens if you get caught up in the friends-with-benefits game and have multiple partners? What happens when the partners you've become addicted and bonded to are gone? You experience withdrawl symptoms in the emotional center of the brain."