But obesity also seems to be occurring even in some domestic and wild animals who aren’t being overfed or under-exercised. If these findings are true, something else must be driving obesity and uncovering those could help tackle our own epidemic with the condition.

More than 1.9 billion human adults are overweight. Of these, more than 650 million are obese – that’s about 13% of the world’s adult human population. The worldwide prevalence of obesity has nearly tripled since 1975. And childhood obesity has risen alarmingly too – an estimated 41 million children under the age of five are overweight or obese.

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The first animal clue lies at the paw of the obesity-prone Labrador retriever. “Labradors are consistently the headline act when it comes to overweight dogs,” says Eleanor Raffan, a veterinarian and geneticist at the University of Cambridge. She and fellow researchers discovered that a genetic mutation present in around a quarter of Labradors, was associated with obesity. For each copy of the mutation – which occurred in a gene called POMC – a dog was about 2kg heavier. Most of the animals the researchers studied had one copy of the mutation, but fewer had two.