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updated 10/14/2013 3:15:39 PM ET 2013-10-14T19:15:39

Apes orphaned by the African bushmeat trade lack the social savvy of apes raised by their mothers, a new study finds. The study links the emotional development of bonobos (Pan paniscus), one of humans' closest living relatives, with the ability to interact nicely with others, echoing how human emotions develop.

Bonobos who are good at soothing themselves out of a bad mood are more likely to comfort other bonobos in distress, researchers report today (Oct. 14) in the journal Proceedings of the National Academy of Sciences.

"By measuring the expression of distress and arousal in great apes, and how they cope, we were able to confirm that efficient emotion regulation is an essential part of empathy," study researcher Frans de Waal, of Emory University's National Primate Research Center, said in a statement.

Though animal emotions "have long been scientifically taboo," de Waal said, he and his colleagues suspected that emotions might have evolved similarly before the bonobo and human lines split about 6 million years ago.

The researchers observed juvenile bonobos at a sanctuary near Kinshasa in the Democratic Republic of the Congo. They watched as the young primates fought, threw tantrums and comforted one another by hugging or stroking. [ See Video of a Bonobo Hug ]

In 373 post-distress interactions (318 caused by fights and 55 caused by tantrums), the researchers found that the better a bonobo was at soothing his or her own emotions, the more likely he or she was to rush to aid a friend in need. A similar pattern is seen in human interactions, the researchers reported.

When orphaned human children are left in institutions and receive little social stimulation or parental nurture, they tend to struggle to form social attachments. The same is true for bonobos, the researchers found. Young orphaned apes were more likely than apes raised by mom to have trouble coping with their own emotions. They showed signs of anxiety, such as scratching, longer after a fight or tantrum, and were also more likely to start screaming again after their initial distress subsided.

Orphaned apes played less than half as much as their counterparts with moms, initiated play half as often and had only a third as many friends, on average. What's more, the orphans were less likely to console another bonobo in distress, likely because seeing another ape upset caused them too much anxiety to handle.

"Empathy allows great apes and humans to absorb the distress of others without getting overly distressed themselves," de Waal said.

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