About the Authors

Matthew W. Campbell

matthew.campbell@emory.edu

Affiliation Living Links Center, Yerkes National Primate Research Center, Emory University, Atlanta, Georgia, United States of America

Frans B. M. de Waal

Affiliation Living Links Center, Yerkes National Primate Research Center, Emory University, Atlanta, Georgia, United States of America

Competing Interests

The authors have declared that no competing interests exist.

Author Contributions

Conceived and designed the experiments: MWC FBMW. Performed the experiments: MWC. Analyzed the data: MWC. Wrote the paper: MWC FBMW.