"Among mice in control groups in the National Toxicology Programme (NTP), there was a 11.8 per cent increase in body weight per decade from 1982 to 2003 in females coupled with a nearly twofold increase in the odds of obesity. In males there was a 10.5 per cent increase per decade."
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.
How do they select the parents of the next generation? At random? Pick the more healthier (i.e. 0.1% more weight)? It's possible to do artificial selection by accident.
The only idea I have to solve this problem is to froze some mice embryos and defrost some of them in 20 years and compare (and some of them in 50 and 100 years).
In the comments of the source article (linked from Marginal Revolution) people working in labs claimed the ingredients in commercial food mixes had changed dramatically since the 80s, even where the supplier remained unchanged and the calories were approximately the same.
Even the bacteria are full. Seriously though, chimps probably have similar intestinal flora as we, and they're the fattest of the fattening animals. See the original paper, they're an order of a magnitude fatter than any other species. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3081766/pdf/rspb...
I propose that the increased population and access to food is accelerating the evolution of intestinal flora, causing it to become more efficient at digesting, sometimes even exceeding the hosts capacity leading to obesity, leaky gut syndrome and IBS.
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.