A study at San Diego State University recently discovered that a previously unknown viral agent living in the gut of over a third of the world’s population may be responsible for the link between obesity and type 2 diabetes.The awkwardly-named virus crAssphage, it turns out, has been around as long as humans have, and may offer a link between diabetes and obesity that overturns the popular assumption that one causes the other.

The finding happened by accident, said SDSU a bioinformatics professor Robert A. Edwards, while researchers were studying 12 DNA fecal samples. The viral DNA cluster was common to samples from obese patients with type 2 diabetes, and had not been previously listed in the database at the National Institutes of Health.

While much research remains, this finding may explain why the correlation between diabetes and obesity is so high, while many obese people do not develop diabetes and some people with type 2 diabetes are not obese or even overweight.