A new study published in the journal Science does nothing to dispel the notion that males who routinely cheat on their mates are just a bunch of rats.

The study examined the DNA of Midwestern prairie voles and linked it to the rodents' behavior. Voles are known for their monogamous pair-bonding, but that doesn't stop a lot of the males from wandering off and sleeping around.

Researchers at the University of Texas at Austin found that one of every three males has a certain hormone in his brain that makes him just plain naughty. Not only were these guys prone to creeping outside of their main relationships, they were so brazen that they often found themselves in nests already occupied by faithful males that beat them to a pulp.

While some of the unfaithful were out fooling around, other unfaithful males slipped into their homes and impregnated their mates. This cycle of strange poetic justice virtually guaranteed that philanderers were more likely to unknowingly help raise young as stepfathers.

The study does more than offer observations on dirty vole behavior. It appears to suggest that vole cheaters are born that way. "Just as people can be introverted or extroverted, prairie voles can be more or less prone to sexual fidelity because of...genetic differences," said a statement by the university that accompanied the study's release late this week.

The researchers found no link between the behavior of voles and that of other animals, humans included. Deep inside its content, buried under a lot of technical words that most people have never heard, their report offered only this this: "Among humans, similar forces have been proposed to explain differences in personality, resilience, and psychiatric risk."

Because sociology is crucial to understanding the ways humans act, the authors said it was surprising that science doesn't know more of the same for other animals. "We may find this to be a common pattern in social behavior, including personality differences, in lots of species," said lead author Steven Phelps, an associate professor of integrative biology.

The study doesn't come to any moral conclusions about whether fidelity and infidelity makes voles naughty or nice. Phelps said both types are important. "Every brain is like a snowflake," he said. "No two are quite the same. Selection favors keeping both types of voles around."

And here's why: Vole populations rise and fall like crazy because predators gobble them like snacks. "Owls eat 'em like cupcakes," Phelps said. "They love 'em."

When the population is high, unfaithful voles have a field day, spreading their seed, making more voles that end up in the stomachs of birds with sharp claws. When populations are low, faithful voles rule, ensuring that females stay impregnated and remain at home to help the young survive.  A community full of faithful males and a few unfaithful ones works for this species.

"Natural selection ...does not appear to favor one set of genetic characteristics over the other but instead allows for the co-existence of the seemingly contrasting traits, creating evolutionary space for both monogamous and non-monogamous voles," Phelps said.

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