A 2015 study of mammoth molars confirmed that "M. columbi" evolved from Eurasian "M. trogontherii", not "M. meridionalis" as had been suggested earlier, and noted that "M. columbi" and "M. trogontherii" were so similar in morphology that their classification as separate species may be questionable. The study also suggested that the animals in the range where "M. columbi" and "M. primigenius" overlapped formed a metapopulation of hybrids with varying morphology. In 2016, a genetic study of North American mammoth specimens confirmed that "M. columbi" and "M. primigenius" interbred extensively, were both descended from "M. trogontherii", and concluded that morphological differences between fossils may, therefore, not be reliable for determining taxonomy. The authors also questioned whether "M. columbi" and "M. primigenius" should be considered "good species", considering that they were able to interbreed after supposedly being separated for a million years, but cautioned that more specimens need to be sampled.