But as some experts put it, defining doggie ancestry can be tricky. “To a large degree, the accuracy of breed composition tests very likely depends on the degree to which a dog is ‘mixed,’” Lauren Baker and Susannah Sample, both of the School of Veterinary Medicine at the University of Wisconsin-Madison, wrote in an email to PopSci. “From a veterinarian’s standpoint, we find these ‘breed identification’ tests are fun for many owners. But having not been evaluated by the scientific community, they shouldn’t be used to alter medical decisions.”