Just like humans, the orangutans that are happier are more likely to live longer, according to a new research.
These results could shed light on how happiness evolved, not just in orangutans but all primates, including ourselves, says Dr. Alexander Weiss, the lead author of the study.
"Already we have shown that certain personality traits linked to happiness share the same genetic basis in humans and chimpanzees," he said.
"Studying these relationships across a wide range of species could yield fascinating insights into the evolutionary bases of happiness, depression and a host of other psychological characteristics that impact the lives of humans and, most likely, a range of other species," he added.
Weiss and colleagues at the University of Edinburgh and the University of Arizona used an innovative approach to assessing happiness by asking keepers who work with orangutans to answer questions on the animals' behalf.
The keepers were asked how often the orangutan was in a good mood as opposed to a bad mood, how much it enjoyed social interactions and whether it was effective at achieving its goals.
Of the 184 orangutans included in the study those which were scored as happier by their keepers were significantly more likely to be alive up to seven years later. The effect remained even when factors such as sex, age and species were taken into account.
The study is published in Royal Society journal Biology Letters.