A passer-by drops something and you spring to pick it up. Or maybe you hold the door for someone behind you. Such acts of kindness to strangers were long thought to be unique to humans, but recent research on bonobos suggests our species is not as exceptional in this regard as we like to think. Famously friendly apes from Africa’s Congo Basin, bonobos will go out of their way to help strangers too, said Jingzhi Tan, a postdoctoral associate in evolutionary anthropology at Duke University. The impulse to be nice to strangers is likely to evolve in species where the benefits of bonding with outsiders outweigh the costs, said Tan, now a postdoctoral scholar at the University of California, San Diego. “All relationships start between two strangers,” Tan said. “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.”