American Gut Project co-director Rob Knight taking a sample from a furry friend. It's one of about 2,000 samples the project has collected so far from humans and their pets.

(Photo: Courtesy of Amanda Birmingham)
Thousands of people -- and their pets -- are making a strange donation to the University of Colorado and they’re paying for the privilege.

The American Gut Project is mapping the genetic structures of the trillions of microscopic creatures that live in our bodies in an effort to crack open some of today’s biggest health questions, like: What causes obesity? Diabetes? Heart disease?

Researchers at CU Boulder say the American Gut Project is the largest crowd-funded science study ever undertaken.