Obesity researcher David B. Allison of the University of Alabama at Birmingham says he discovered data on small primates -- marmosets -- showed pronounced weight gain over time.
Allison tracked down previous studies of mammals, living with or around humans for at least a decade, and found 12 groups of animal data sets -- involving 20,000 animals. He divided the data into male and female populations and ended up with 24 data sets.
The data ranged from laboratory research animals such as monkeys, chimpanzees and rodents, to feral rats caught in the alleys of Baltimore to veterinary hospitals records on dogs and cats. All 24 data sets had overall weight gain over time and 23 of the 24 had an increase in the percentage of obese individuals in the group.
"There was no single thread running through all 24 data sets that would explain a gain in weight," Allison says. "The animals in some of the data sets might have had access to richer food, but that was not the case in all data sets. Some of the animals might have become less active, but others would have remained at normal activity levels. Yet, they all showed overall weight gain."
The findings are published in the British journal Proceedings of the Royal Society B.