Additionally, According to Gordon Gallup, an evolutionary psychologist at the University of Albany, you can tell by more about someone's sexual history by their handshake. He links a firm handshake (in men) to a host of factors: longevity, bone density, fat mass, and sexual behavior. Men with firm handshakes have more sexual partners, and begin having sex earlier.
Finally, this study from 2009 suggests that there is a correlation between a man's lean muscle mass and his sexual history: Specifically, more muscular men have more partners and begin having sex earlier.
All three studies have their limitations and raise questions, and could be subject to all kinds of scrutiny. I have only one that I would like to raise--that correlation is not the same as causation. In other words, while these studies look at the correlation between certain seemingly unrelated factors (1) and sexual behavior, there is nothing beyond speculation that accounts for this correlation. Evolutionary psychologists are likely to argue that anything that increases mating behavior is likely to be beneficial for an individual's chance at passing genes on, and thus the connection is in some way related to biological attraction. (One of the articles goes so far as to suggest just this--that the factor studied shows that the individual is more likely to be robust and to produce healthy offspring.) However, it could also be that definitions of masculinity and femininity in our culture account for these distinctions, as well. It could also be that our culture has evolved to value some traits over others, and the difference is related to natural selection, but cultural natural selection and not biological natural selection.
1) I say "seemingly unrelated," but I posted the article about men with more muscle mass having more sex to my Facebook, and my friends commentary could be summed up as, "Well, duh." Apparently, that connection is not seemingly unrelated.