Check out this article about this research that indicates that "curvy" women (that is, those with large breasts and a narrow waist) are more fertile.

From The Economist piece:

In the case of progesterone, both groups of narrow-waisted women had high hormone levels. In that of 17-b-oestrodiol, those with narrow waists and large breasts had elevated levels—and that level was particularly high at the time of ovulation...such women are three times as likely as the others to become pregnant on any given occasion.

Don't blame tits-men for their shallowness, blame evolution!

Of course, that begs the question, why do any women have small breasts or wider waists? There is some evidence that women with higher waist-to-hip ratios have more sons than daughters, so there might be evolutionarily stable strategies at play. That might explain the anecdotal impression that many people have that average body shapes differ by population.

Update: FuturePundit points me to this article, where the researcher seems to be limiting the relevance of the finding to Europeans.