Science proves our wild horses, the only species of horse that survived beyond the Pleistocene Era is our native North American horse, whether it went extinct or not and was subsequently brought back matter little in classifying them as native. At a minimum a reintroduced native species.
The Chart of the history of Equine evolution can be seen at: North American Native Horse Evolutionary chart
The chart gives you important events and changes in the Equine species, genus, teeth, toes, eating habits, size and many more details that outline how horse went from several different genus to one at the end of the Pleistocene era.
Given that the biological changes to the Equus genus, the only genus left at the end of the Pleistocene, to warrant a new genus of horse. Taking into consideration that the behavior has remained the same in the wild, such as the formation of familial hierarchy, also proves that the domestication of horse did not create biological changes in equus. We know that no amount of taming of wild horse changed equus and created another genus.
The breeding of wild horses to eliminate an undesirable trait, or enhance a desired trait has created different breeds such as thoroughbreds or draft horses. However breeding for traits also does not mean we have a different genus.
The theory that is repeated among most opponents of the native status of today’s wild horses is generally that the horses went extinct here at the end of the Pleistocene era. However, the original time period they were thought to be gone was ten thousand years, and that time is continually being shortened with fossil find, mitochondrial studies, petroglyphs and Indian oral history.
If horses did go extinct for a time period, which is now only 7,500 years, it is an evolutionary drop in the bucket when considering horses evolved in North America for 56 million years before that. The statement made then by adversaries is that the wild horses of today are horses that were brought back by the Spanish Conquistadors. If that proves to be the case then the language “brought back” means that at a minimum our wild horses, even if they did in fact escape their domestic captors, are at a minimum a reintroduced native species. Because as previously mentioned, no amount of domestication created a new genus of horse.
MANAGED TO EXTINCTION? A 40th Anniversary Legal Forum assessing the 1971 Wild Free-Roaming Horses & Burros Act TRANSCRIPT: ROSS MACPHEE, Curator, Division of Vertebrate Zoology, American Museum of Natural History (AMNH)