Edwin van Leeuwen from the Comparative Cognitive Anthropology Research Group at the Max Planck Institute for Psycholinguistics, said that orphaned chimpanzees had more difficulties to successfully coordinate their social play interactions.
He said that since social play comprises a complex context in which signals about intentions need to be communicated, it seems that orphaned chimpanzees have missed out on valuable lessons from their mothers.
Van Leeuwen and his co-authors Innocent Mulenga and Diana Lisensky compared the play behaviour of 8 orphaned and 9 mother-reared juvenile chimpanzees at the Chimfunshi Wildlife Orphanage Trust in Zambia.
In this institution the orphan chimpanzees are initially cared for by humans. As soon as they are strong enough - usually with one or two years of age - they grow up in an orphan chimp group.
Based on previous research, the scientists expected the orphaned juveniles to play less frequently and smoothly than the mother-reared chimpanzees: After all, the orphans had missed their most important caretaker throughout a sensitive socialisation period, and continued to lack a safe and facilitating social environment provided by their mothers.