Alex Tabarrok has a pretty interesting post today about the peculiar obesity epidemic among animals. It turns out that both pets and feral animals (like sewer rats) have been steadily gaining weight over the past few decades. But before you jump in and take a guess at why, it also turns out that lab mice used as controls in experiments are getting heavier too. This is hard to explain, since researchers have done their best not to change the way they treat control mice:
Control mice are typically allowed to feed at will from a controlled diet that has not varied much over the decades, making obvious explanations less plausible. Could mice have gained weight due to better care? Possibly although that is speculative.
More generally, there are specific explanations for the weight gain in each of the animal populations, just as there are for humans. Each explanation looks plausible taken on its own but is it plausible that each population is gaining weight for independent reasons? Could there instead be a unifying explanation for the weight gain in all populations? No one knows what that explanation is: toxins? viruses? epigenetic factors? I am not ready to jump on any of these bandwagons and in some cases the author’s samples are small so I am not yet fully convinced of the underlying facts, nevertheless this is intriguing and important research.
So what's going on? So far, it's a mystery, though I agree with Tabarrok's skepticism that lots of different populations (humans, pets, wild animals, control mice) are all getting fatter and all for different reasons. It just seems a little too pat. But you never know.
As an aside, I wonder if this kind of weight gain has been observed in any non-mammal populations?