Xspider1 its going to have to be a pretty extreme and extensive mutation for an individual to be deemed a unique species. The mutations would have have to be extensive enough to disguise the markers used to differentiate the original species, and I have hard time envisioning that occurring in anything but like bacteria, or fruit flies at best with their four chromasomes...maybe.... I'd think most mutations that would cause drastic morphological changes will prove lethal from the get go or shortly there after, unless, of course its the result of direct genetic manipulation recombining the genes of disparate species in a plotted out effort, but even then the original species involved could be identified. Were it by just a single inheritable trait that sasquatch is set apart from modern humans then it might well be attributed to an aberrant mutation, but there's clearly more involved in the differentiation between us.