You’re tired and have had a long day, but you need to pack into a full bus to get home. One stranger notices that you need a break and offers you his or her seat. Or you are at the check out line at the grocery store with just a carton of milk and the person before lets you go ahead of them. Humans pick up on social cues and may go out of their way to help a stranger. It turns out that we’re not the only ones that do this, bonobos also help strangers without being asked.

Bonobos have already been known to share food with strangers so Jingzhi Tan, a postdoctoral associate in evolutionary anthropology at Duke University, led a study to see how willing they are to help strangers out. The 16 bonobos used in this study were born in the wild and studied at the Lola ya Bonobo sanctuary in the Democratic Republic of Congo.

The set-up was made up of two rooms that were separated by a fence. A bonobo was placed in the first room without any food. In the next room, an apple was hanging down from a rope, which the ape could see but not access. What they could do, was climb the fence and remove the wooden pin holding the rope to the ceiling and letting it drop to the floor in the next room. Bonobos were introduced one at a time into the empty room. The bonobos in the first room released the fruit four times more often when an unknown bonobo was in the room than when the room was empty. Even if they don’t benefit and are not asked, bonobos will help a stranger to get food.

Bonobos are willing to help a stranger out. Image credits: Max Pixel.

In another experiment, the researchers added a fence with larger holes so that the strangers could stick their arms through and beg for food. The bonobos in the first room still helped as often if they were asked or not.

The bonobos may have subconscious emotional empathy because when they watched videos of known and unfamiliar bonobos yawning or making neutral expressions, they mirrored them. Yes, yawning is apparently also contagious for bonobos. Strangers’ yawns were as contagious as groupmate’s yawns. In this way, bonobos are also very similar to humans.

For bonobos being nice seems to have benefits in the long run, or else it wouldn’t have evolved. Females leave their family group to join a new group later in life. So for them, it could be beneficial, and important to their future survival, to be nice to strangers, especially when it has no cost.

“All relationships start between two strangers. You meet a stranger, but you may meet them again, and this individual could become your future friend or ally. You want to be nice to someone who’s going to be important for you ,” explained Tan, a postdoctoral scholar at the University California, San Diego.

It is similar in humans too. Though we will likely never see the stranger that we helped carry something heavy or held the door open for again, we hope, to some degree, that someone will help us at some point to make things a bit easier.

Journal reference: Jingzhi Tan et al, Bonobos respond prosocially toward members of other groups, Scientific Reports (2017). DOI: 10.1038/s41598-017-15320-w