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If the age-old adage "once a cheater, always a cheater" is true, the findings detailed in David P. Barash's book Out of Eden could mean many of us are, well, screwed.

According to Barash, a psychology professor at the University of Washington in Seattle, the simple truth (and in many ways "it's complicated" truth) is that monogamy can be more of a societal pressure than a biological inclination.

"When people of either gender act on their polygamous inclinations while living in a monogamous tradition, they are being unfaithful to their sociocultural commitment, but not to their biology," Barash writes, in an excerpt published on Salon.

Live Science reports that only between 3 and 5% of mammalian species mate for life. But Barash said statistics like these aren't as clear-cut as they seem: Over the years, scientists have determined there's a crucial difference between social monogamy and sexual monogamy, the latter being far less common.

For humans, a departure from monogamy can mean exploring other romantic arrangements.

While only 15% of Americans 18 to 29 say they would consider an open relationship, 4 to 5% of the U.S. population identifies as polyamorous, and many more are experimenting with the nearly infinite possibilities for relationships.

Barash said polyandry and polygyny will be a slippery slope in societies that reward monogamy. But most of us will at some point find ourselves somewhere between these two poles.

"We have tendencies in both directions: We want to pair up with people, we want to make commitments to each other and have a sense of safety and security," Tao Ruspoli, the documentarian behind Monogamish told Mic's Kate Hakala in 2015. "But we also have other desires to explore, have a sense of mystery in our lives and obviously keep our sexuality alive. So the question is, how do we negotiate all those tensions?"