* By Brian Williams
* From: The Courier-Mail
* December 13, 2010 7:42AM
THE obesity epidemic seen in humans and their pets may be caused by more than rubbish diets and lack of exercise.
Some scientists think it may be due to a combination of issues, including viruses or something else that affects cells or organs.
This is opposed to the commonly held belief based on poor Western lifestyles that feature over-eating, little exercise and fatty foods.
Scientists' curiosity was triggered when they noticed laboratory rats and mice on strict diets had put on weight just as domestic pets and feral animals living around humans had.
They looked at more than 20,000 animals from 24 populations of eight species living in or around industrialised societies.
Scientists from nine research centres across the world found that in all cases, body weight was increasing.