Heterosexual women, Dr. Chivers and her colleagues found, were no more excited by athletic naked men doing yoga or tossing stones into the ocean than they were by the control footage: long pans of the snowcapped Himalayas. When straight women viewed a video of a naked woman doing calisthenics, on the other hand, their blood flow increased significantly.

What really matters to women, Dr. Chivers said, at least in the somewhat artificial setting of watching movies while intimately hooked up to a device called a photoplethysmograph, is not the gender of the actor, but the degree of sensuality. Even more than the naked exercisers, they were aroused by videos of masturbation, and more still by graphic videos of couples making love. Women with women, men with men, men with women: it did not seem to matter much to her female subjects, Dr. Chivers said.

“Women physically don’t seem to differentiate between genders in their sex responses, at least heterosexual women don’t,” she said.