In the Harvard University lab of biologist Catherine Dulac, some of the female mice act peculiarly like males. When other mice enter their enclosure, these females squeak like male mice, sniff around the intruders’ backsides, and attempt to copulate. The only thing distinguishing these gender benders from normal female mice is the absence of a working vomeronasal organ, or VNO—a tiny structure that senses pheromones, the chemicals known to influence the sexual behavior of mice.
Biologists have long suspected that the male mouse brain is cued by testosterone to develop circuitry for male sex behaviors like rump sniffing. Dulac’s study—which used genetic manipulation and surgery to create VNO-less female mice—reveals that the circuitry for male behaviors appears to be present in all mouse brains. The role of pheromone reception in females may be simply to flip a switch that suppresses the male circuit in the female brain. But what works in mice most likely wouldn’t in humans. “Rodents are extremely olfactory,” Dulac says, while “humans are more sensitive to visual cues.