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12-07-2011 | Article

Happiness is key to longevity for orangutans

Abstract

Free abstract

MedWire News: The subjective wellbeing of orangutans is a valid indicator of their welfare and longevity, according to a study by UK and US researchers.

They say that, as in humans, happiness appears to be linked to a longer life, an observation that underscores the importance of monitoring the wellbeing of animals in captivity.

The research was undertaken by psychologists at the University of Edinburgh, UK, and the University of Arizona, Tucson, USA. The team sought to determine whether the subjective wellbeing of nonhuman primates was associated with longevity, as it is known to be in humans.

They prospectively studied 184 orangutans housed in 42 zoological parks around the world. Each animal's primary keeper (ie, the zoo employee who was most familiar with the animal's behavior and affect) completed a 4-item subjective wellbeing questionnaire.

The questionnaire was adapted from one used to assess humans and covered the frequency of positive versus negative moods, pleasure derived from social interactions, ability to achieve goals, and the keeper's impression of how happy they would be if they were the animal for a short period of time.

The orangutans were followed-up for approximately 7 years, during which time 31 died. The average time between the questionnaire completion and death was 3.7 years.

The researchers examined a number of characteristics in relation to subsequent mortality. They found that male animals were two-and-a-half times more likely to die than females and that each 1-year increase in age was associated with a 10% increased risk for dying.

Furthermore, orangutans with higher ratings of subjective wellbeing were less likely to die over the follow-up period; each 1-standard deviation (SD) increase in wellbeing score was associated with a 42% reduction in risk for dying.

Indeed, the effect of a 1-SD increase in wellbeing was equivalent to being 11.34 years younger, the team calculated.

Writing in the journal Biology Letters, Alexander Weiss and co-authors say there are several possible explanations for the relationship between wellbeing and longevity.

Behavioral indicators of low subjective wellbeing in orangutans may reflect behavioral reactions to the subsyndromal stages of disease or other health problems. Alternatively, lower subjective wellbeing may reflect the presence of stressors that lead to chronic hypothalamic-pituitary-adrenal axis activation, which, in turn, generates greater allostatic load and poorer health.

A third possibility, which is consistent with the heritability of subjective wellbeing, is that subjective wellbeing is a marker of genetic quality that evolved via sexual selection.

"This finding also has important practical implications. Specifically, it suggests that impressions of the subjective wellbeing of captive great apes are valid indicators of their welfare," write Alexander Weiss and co-authors.

They conclude: "A quick, easily administered four-item questionnaire could provide important diagnostic information useful for making decisions about health monitoring, assessing the efficacy of enrichment, and otherwise ensuring that, orangutans, too, live 'happily ever after'."

MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011

By Joanna Lyford