Phew!

Did you knowwwwwwww...

That body odor is an evolutionary deterrent against inbreeding and incest?  I believe the founding study indicating this can be found in a paper by Wedekind et al. (1995) entitled "MHC-dependent mate preferences in humans." If you don't feel like reading up, essentially what happens is that women prefer the b.o. of men who are less genetically similar to themselves. (The study is, however, pretty interesting, both in specific conclusions and inferences as well as in experimental design, so if you've got the time, do a quick Google Scholar search.) Intriguingly, this preference seems to reverse when women are on birth control, a fact which some scientists interpret by saying that the hormonal changes induced mimic pregnancy, which is a time where human females benefit most from being in a protected family group. ...At this point, the feminists are starting to take up arms, so I'll just stop here with a warning about defining motives behind apparent evolutionary trends.

Anyway, if you're interested in human sexual attraction, genetics, and evolutionary science, check out some of these related articles by Hedrick and Loeschcke 1996, Herz and Cahill (1997), Gangestad and Thornhill (1998), or do a search for more recent literature on PubMed or Google Scholar, or if you're feeling curious but overwhelmed, here's a decent (and much less scientific) introductory article.