Just like humans, monkeys prefer to keep their private lives private--especially when it comes to sex, according to a new study from scientists at Utrecht University and the Biomedical Primate Research Centre in the Netherlands.

Other animals seem perfectly happy to do the nasty in public, so why exactly would monkeys prefer secrecy? The researchers suggested that the sneaky copulation happens to be opportunistic rather than intentional. That is, as males and females seek sex partners, they have a better chance of hooking up when there's no competition around to get in the way.

"By concealing sexual behaviour, females and subordinate males try to reduce harassment from group members," study co-author Anne Overduin-de Vries, a doctoral student at the university, told the AFP in an email. "Although harassment is not frequent, it may have serious consequences such as getting injured or not being able to finish a copulation."

For the study, 27 long-tailed macaques (15 females, seven males, and five babies) were observed. The researchers found that, yes, copulating "in public" often leads to harassment and that both males and females initiated sex less often when other macaques were present.

"Given that long-tailed macaques are a quite promiscuous primate species, it was surprising that hiding their copulations was so prevalent, in particular for so many group members," study co-author Dr. Liesbeth Sterck, an associate professor at the university, told The Huffington Post in an email, but added, "Also in macaques the dominant male can copulate in the sight of group members."

The study was published online in the journal Behavioral Ecology and Sociobiology.

Editor's Note: This article was updated to include comment from Dr. Liesbeth Sterck.

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  • Riding a Segway

  • Gaming

  • Cooking

  • Skateboarding

  • Karate

  • Drinking

  • Cooling Off

  • Babysitting

  • Laughing

  • Smoking

  • Biking

  • Painting

  • Tug-of-War

  • Walking Upright

  • Making Out?

  • Smiling