The following is based on Van Buren and has not been confirmed by canon sources.
Mutant cannibals are one of the results of environmental disaster in the Grand Canyon. Their mutation is characteristic of its place of origin. Mutant cannibals are about 5 ft. tall. While their jaws remained normal-sized, the craniums are visibly oversized. Moreover, their fingers are very long and their nails turned to claws. Dark skin and bulging eyes are also typical.