 The quality of the relationship seemed to play an important role in the maintenance of cooperation over time.Rekers, Haun, and Tomasello tested the cooperation abilities and preferences of humans ("Homo sapiens") and compared them to chimpanzees.The researchers provided 24 three-year-old children with some basic training in pulling food rewards towards themselves; in pairs using a loose-string setup, and solo training in which the two ends of a rope were tied together.