It's no secret that people select mates in part for traits they want to pass on to their descendants. However, a lot of studies show that such traits are closely tied to attractiveness--i.e., the traits that are considered attractive are precisely those that favour childbearing and producing fit, healthy offspring. That's why the suggestion that some women will be chosen more often than equally attractive alternatives puzzled me. I wanted to know what the X factor was and why it can't be subsumed under "attractiveness."