In 2010, parody news site The Onion posted this little gem. Undoubtedly inspired by media buzz about creatures like Koko the Gorilla and the researchers who study them, this satirical piece explores the morality of teaching sign language to (or having complex discussions with) non-human primates. Now, it seems like there may actually be more truth to the jab than was previously suspected. While there is no direct evidence of suicide in either wild or captive great apes, the mid-life years may be a time of significant stress.
In November of 2012, the Proceedings of the National Academy of Sciences published a study which suggests that captive apes show aging and developmental patterns which more closely resemble the lives of modern humans than might previously have been suspected. The apes were reported to have seemed to be happier in youth, more stressed as adults and then happier again as they progressed into a more advanced age. The study investigated two samples of chimpanzees and one sample of orangutans, two of the great apes whose genetic make-up is some of the most similar to humans'. Approximately 508 animals were included in the study.
So, how does a scientist determine the criteria for gauging emotional satisfaction in a great ape? The authors of the study gathered information from zookeepers, researchers, and other volunteers who used a questionnaire format commonly used to assess human satisfaction, but which was also stated to be serviceable for evaluation of great apes. Based on the answers of their caretakers, it seems that chimps and orangutans start experiencing losses of energy, less social interaction and decreases in overall motivation at approximately the age of 30. They often seem to regain these things as they move into later years, researchers say, often after the grandchildren are born or start to mature. This overall dynamic is similar to events which human beings often experience, which will very likely influence many future discussions about the welfare of captive apes.
The study did not investigate any types of wild primates, so there is no control by which to determine whether or not this dynamic appears or significantly differs in non-captive animals. How much of the study's finding is nature, then, and exactly how much is nurture? Given the increased access to veterinary care and close proximity to humans experienced by captive apes and the inherent difficulty of observing wild animals without having at least a slight impact on their natural habitats, researchers may never truly know for sure.
The study in question was primarily arranged by Prof. Andrew Oswald from the University of Warwick and Dr. Alexander Weiss of the University of Edinburgh. It was then edited by Nobel Prize winner Prof. George A. Akerlof of University of California, Berkeley. More information can be found online at pnas.org.