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Everyone knows Americans are fat and getting fatter, and everyone thinks they know why: more eating and less moving.

But the “big two” factors may not be the whole story. Consider this: Animals have been getting fatter too. The National Pet Obesity Survey recently reported that more than 50 percent of cats and dogs – that’s more than 80 million pets – are overweight or obese. Pets have gotten so plump that there’s now a National Pet Obesity Awareness Day. (It was Wednesday.) Lap dogs and comatose cats aren’t alone in the fat animal kingdom. Animals in strictly controlled research laboratories that have enforced the same diet and lifestyle for decades are also ballooning.

In 2010, an international team of scientists published findings that two dozen animal populations – all cared for by or living near humans – had been rapidly fattening in recent decades. “Canaries in the Coal Mine,” they titled the paper, and the “canaries” most closely genetically related to humans – chimps – showed the most troubling trend. Between 1985 and 2005, the male and female chimps studied experienced 33.2 and 37.2 percent weight gains, respectively. Their odds of obesity increased more than 10-fold.

To be sure, some of the chimp obesity crisis may be caused by the big two. According to Joseph Kemnitz, director of the Wisconsin National Primate Research Center, animal welfare laws passed in recent decades have led caretakers to strive to make animals happier, often employing a method known to any parent of a toddler: plying them with sugary food. “All animals love to eat, and you can make them happy by giving them food,” Kemnitz said. “We have to be careful how much of that kind of enrichment we give them. They might be happier, but not healthier.”