A new study on the behavior of chimpanzees suggests that the friendships between chimpanzees are based on trust, Phys reports

The report was published in the Cell Press journal Current Biology on January 14.

"Humans largely trust only their friends with crucial resources or important secrets," says Jan Engelmann of the Max Planck Institute for Evolutionary Anthropology in Germany.

"In our study, we investigated whether chimpanzees show a comparable pattern and extend trust selectively toward those individuals they are closely bonded with. Our findings suggest that they do indeed, and thus that current characteristics of human friendships have a long evolutionary history and extend to primate social bonds."

For the study, Engelmann and Esther Herrmann observed the interactions of 15 chimpanzees living at Sweetwaters Chimpanzee Sanctuary in Kenya over a 5-month period.

Four researchers collected observational data on the chimpanzees from December 2014 to May 2015 on activities like grooming, co-feeding, physical contact and arms-length proximity, Meta Science News reports.

After observing experimental interactions between the chimps, the researchers suggested that there was greater trust between friends than non-friends.

As the researchers explain it, "chimpanzees were significantly more likely to voluntarily place resources at the disposal of a partner, and thus to choose a risky but potentially high-payoff option, when they interacted with a friend as compared to a non-friend."

"Human friendships do not represent an anomaly in the animal kingdom," Engelmann says.

"Other animals, such as chimpanzees, form close and long-term emotional bonds with select individuals. These animal friendships show important parallels with close relationships in humans. One shared characteristic is the tendency to selectively trust friends in costly situations."

Engelmann and Herrmann said that they would like to further investigate the similarities between close relationships in humans and chimpanzees.