It sounds like something out of the satirical journal Annals of Improbable Research: a team of Swedish neuroscientists scanned people's brains as they smelled a testosterone derivative found in men's sweat and an estrogen-like compound found in women's urine. In heterosexual men, a part of the hypothalamus (the seat of physical drives) responded to the female compound but not the male one; in heterosexual women and homosexual men, it was the other way around. But the discovery is more than just a shoo-in for that journal's annual Ig Nobel Prize - it raises provocative questions about the science and ethics of human sexuality. | 
