Cameron Muir thinks a lot about hot, sweaty sex. It’s his job, after all. Muir is a psychologist at Brock University, and his current fascination is human sweat — particularly when it’s coitus-induced. His interest in sweat was aroused by steroid hormones, the tiny molecules like testosterone and estrogen that control so much of human sexuality from the inside of our bodies. Testosterone, in particular, can profoundly change a person’s appetite for sex. Women who have had their ovaries removed often complain they’ve lost their libidos, probably because of changes in hormone concentrations. “They’ll go to the doctor and say…