rhesus monkeys

Macaques use stones as hammers to smash open food items like shellfish and nuts. Lydia V. Luncz hide caption

A rhesus macaque monkey grooms another on Cayo Santiago, off the eastern coast of Puerto Rico. Brennan Linsley/AP hide caption

Gregoire Courtine, a neurologist at the Swiss Federal Institute of Technology, holds a silicone model of a primate's brain with an electrode array. The goal is to pick up signals from the brain and transmit them to the legs. Alain Herzog/EPFL hide caption

Family means a lot on Cayo Santiago, an island and monkey research colony off the coast of Puerto Rico. The colony of rhesus macaques living on the island since the 1930s has allowed scientists to trace kinship ties and effects across an extended community. Anders Kelto/NPR hide caption