Brendan Zietsch and Pekka Santtila set out to prove if "women simply happen to share biology with men, for whom orgasm is important," making it "an accidental byproduct, like men’s nonlactating nipples." They surveyed 1,803 pairs of opposite-sex twins and 2,287 pairs of same-sex twins:
[W]hile orgasmic function was genetically shared in same-sex twins — brother tended to share function with brother, or sister with sister — the relationship vanished in opposite-sex twins, though both share the same amount of genetic material. The underlying genetics, and thus the underlying evolutionary pressures, thus appear to differ. "This does not support the hypothesis that female orgasm is maintained only as a byproduct of selection on the male orgasm," wrote Zietsch and Santtila.
The Dish 