It makes sense that humans, like any animal, would feel the drive to propagate their own genes. But it has long been an article of faith, rather than science, that women feel more pressure to do so than men due to their reproductive limitations. Menopause ends the possibility of reproduction for cisgender women. Cis men can, in theory, reproduce forever. And, as it turns out, they have more of a longing to reproduce as they get older.

How Does Baby Fever in Men Work?

Researchers have found that male baby fever presents differently than female baby fever. Although women desire children less as time goes on, men want more progeny as they age and begin building families. “How frequently women have the desire to have a child goes down with age, and down as they actually have children,” Gary Brase, Ph.D., a psychologist at Kansas State University, told Live Science. “For men, it tends to go up.” One thing that seems to make a man’s biological clock tick is, well, women. National studies of Finnish couples have found that baby fever in men typically arises during conscious attempts to conceive, which are often dictated by the woman’s desire to have a baby. Simply put, baby fever is contagious. One recent study supports this notion. Researchers found that younger women paired with older men were less fertile than expected, and older women paired with younger men were more fertile than expected. Laura Dodge, Sc.D., a professor of reproductive biology at Harvard Medical School who led the research, suspects this is because straight couples in which the woman is reaching the end of her reproductive life feel more pressure to conceive. “The impact of age seems to focus almost exclusively on the female partner’s biological clock,” Dodge told The Guardian. “When making this decision, they should also be considering the man’s age.”

The Science of the Biological Clock in Men

Another factor contributing to baby fever in older men, observed by Brase and colleagues in U.S.-based samples, is a simple cost-benefit analysis. As men grow older, they tend to achieve more in their careers. The costs of having a child (financial and professional) diminish, relative to the benefits. In this way, baby fever may be less about gender than socioeconomics. “Gender role norms didn’t do much as far as explaining people’s desire to have a baby,” Brase says. It’s important to note that some men don’t need partners who want children in order to experience baby fever. It’s possible that the biological clocks of these men are powered by the need to assert their masculinity. Providing, protecting, and procreating are three core cultural dimensions of masculinity, after all. Which means there’s nothing more masculine than catching baby fever.