“One might think that something like mammalian monogamy would be nothing like fish monogamy—that we would use higher, more complex processes,” says Justin Rhodes, a biologist studying genes affect behavior at the University of Illinois at Urbana-Champaign, but who was not involved in the study. “But this work is saying, well, no. There’s a lot of common molecules involved.”

Among the genes that rose to prominence in steadfast species were factors that are thought to affect learning and memory, or make the brain more amenable to change—hinting at a sort of behavioral flexibility in monogamous males. Young thinks it’s possible that hardworking family guys may benefit from this kind of cognitive firepower.

Until these genes are tested one by one, however, it’s too early to definitely say what’s actually going through the heads of monogamous males. “A clear next step could be manipulating these genes and seeing if that changes behavior,” Hoekstra says. “Can you get a promiscuous male to start providing parental care? That would be really cool.”

Of course, even if there are commonalities between species, the complexity of the researchers’ findings also shows that there isn’t just one “monogamy gene”—or even one way to be monogamous. “There’s a conserved theme at the molecular level, but also a lot of variation on that theme... even within populations and individuals,” Hofmann explains.

For instance, “monogamous” isn’t always equivalent to “faithful”: The term refers not to a code of conduct, but a repetitive pattern of behavior. Getting attached to a single mate at a time certainly doesn’t preclude the tendency to stray—and many monogamous animals regularly engage in a little infidelity here and there.

Tinkering aside, monogamy’s encore act is telling, Hofmann says. The packaging may differ, but these sorts of evolutionary echoes indicate that, with the same building blocks lying around, there’s been little reason to reinvent the wheel.

Moving forward, the researchers plan to test if these patterns hold true in other monogamous species. “I think we would go in with the prediction that we’d see the same genetic signature in other vertebrates,” Young says.

Does that include primates—like us humans? It’s complicated. The topic of human monogamy remains a contentious topic: On one hand, people do tend to get pretty attached to each other, and fathers regularly parent their kids. But not all hallmarks ring true—and many human cultures aren’t strict about the practice of monogamy.

The researchers didn’t include people in their study for a variety of reasons (including the ethical dubiousness of grinding up the brains of virile young men). Still, humans are vertebrates, and we share much of the anatomical and chemical machinery that enables monogamy in other species. As such, there are likely to be at least some overlaps in behavior, Hofmann says.

From the outside, animals take just about every shape and form. But deep down—at the heart of it all—there exist some striking similarities. “We’re not apart from other animals,” Hofmann says. “We are animals. What happened millions of years ago still affects what we look like, our physiology, our behavior. And not acknowledging that is a mistake.”