Are North America’s Wild Horses Native?


The fake science of invasive species biology classifies horses as “invasive” “exotics” that “compete” with “natives” to “harm” “ecological systems”. These terms are neither scientifically defined, nor consistently applied.

As Dan Flores, author of American Serengeti observes, “Neither paleontology nor molecular genetics lends any support whatsoever to the idea that horses evolved into their modern form anywhere but in North America. Nonetheless, most state and federal land agencies continue to insist that horses, with 50 million years of evolutionary history here, are still “non-native”.

Horses are beneficial to Western ranges and wildlife because they and their ancestors co-evolved – over millions of years – to be complimentary – not competitive – with other native plants and animals.

NOTE: this post initially appeared on on October 7, 2014

Yukon Horse.

Should the wild horses that roam North America be considered native wildlife?

They may have been “introduced” by man, but scientific evidence suggests that they are genetically the same as the horses that became extinct on the continent between 11,000 and 13,000 years. In fact, the genus Equus could have been wiped out entirely had it not crossed the Bering Stait land bridge into Eurasia. Jay F. Kirkpatrick, Ph.D. and Patricia M. Fazio, Ph.D.* look at the evidence.

Are wild horses truly “wild,” as an indigenous species in North America, or are they “feral” weeds – barnyard escapees, far removed genetically from their prehistoric ancestors? The question at hand is, therefore, whether or not modern horses, Equus caballus, should be considered native wildlife.

The genus Equus, which includes modern horses, zebras, and asses, is the only surviving genus in a once diverse family of horses that included 27 genera. The precise date of origin for the genus Equus is unknown, but evidence documents the dispersal of Equus from North America to Eurasia approximately 2 to 3 million years ago and a possible origin at about 3.4 to 3.9 million years ago. Following this original emigration, several extinctions occurred in North America, with additional migrations to Asia (presumably across the Bering Land Bridge), and return migrations back to North America, over time. The last North American extinction occurred between 13,000 and 11,000 years ago.¹

Had it not been for previous westward migration, over the land bridge, into northwestern Russia (Siberia) and Asia, the horse would have faced complete extinction. However, Equus survived and spread to all continents of the globe, except Australia and Antarctica.

In 1493, on Columbus’s second voyage to the Americas, Spanish horses, representing E. caballus, were brought back to North America, first in the Virgin Islands, and, in 1519, they were reintroduced on the continent, in modern-day Mexico, from where they radiated throughout the American Great Plains, after escape from their owners.²

Critics of the idea that the North American wild horse is a native animal, using only paleontological data, assert that the species, E. caballus (or the caballoid horse), which was introduced in 1519, was a different species from that which disappeared 13,000 to 11,000 years before.

Late Pleistocene horse skull, Equus lambei, from the Klondike region, Yukon.

Herein lies the crux of the debate.

However, the relatively new (27-year-old) field of molecular biology, using mitochondrial-DNA analysis, has recently found that the modern or caballine horse, E. caballus, is genetically equivalent to E. lambei, a horse, according to fossil records, that represented the most recent Equus species in North America prior to extinction. Not only is E. caballus genetically equivalent to E. lambei, but no evidence exists for the origin of E. caballus anywhere except North America.³

According to the work of Uppsala University researcher Ann Forsten, of the Department of Evolutionary Biology, the date of origin, based on mutation rates for mitochondrial-DNA, for E. caballus, is set at about 1.7 million years ago in North America. Now the debate becomes one of whether the older paleontological fossil data or the modern molecular biology data more accurately provide a picture of horse evolution. The older taxonomic methodologies looked at physical form for classifying animals and plants, relying on visual observations of physical characteristics. While earlier taxonomists tried to deal with the subjectivity of choosing characters they felt would adequately describe, and thus group, genera and species, these observations were lacking in precision.

Reclassifications are now taking place, based on the power and objectivity of molecular biology. If one considers primate evolution, for example, the molecular biologists have provided us with a completely different evolutionary pathway for humans, and they have described entirely different relationships with other primates. None of this would have been possible prior to the methodologies now available through mitochondrial-DNA analysis.

Carles Vila, also of the Department of Evolutionary Biology at Uppsala University, has corroborated Forsten’s work. Vila et al have shown that the origin of domestic horse lineages was extremely widespread, over time and geography, and supports the existence of the caballoid horse in North American before its disappearance.4

Finally, the work of Hofreiter et al,5; examining the genetics of the so-called E. lambei from the permafrost of Alaska, found that the variation was within that of modern horses, which translates into E. lambei actually being E. caballus, genetically. The molecular biology evidence is incontrovertible and indisputable.

The fact that horses were domesticated before they were reintroduced matters little from a biological viewpoint. They are the same species that originated here, and whether or not they were domesticated is quite irrelevant. Domestication altered little biology, and we can see that in the phenomenon called “going wild,” where wild horses revert to ancient behavioral patterns. James Dean Feist dubbed this “social conservation” in his paper on behavior patterns and communication in the Pryor Mountain wild horses. The reemergence of primitive behaviors, resembling those of the plains zebra, indicated to him the shallowness of domestication in horses.6

An artist’s impression of the Yukon Horse, dating back 26,000 years. © Yukon Beringia Interpretive Centre

The issue of feralization and the use of the word “feral” is a human construct that has little biological meaning except in transitory behavior, usually forced on the animal in some manner. Consider this parallel. E. Przewalski (Mongolian wild horse) disappeared from Mongolia a hundred years ago. It has survived since then in zoos. That is not domestication in the classic sense, but it is captivity, with keepers providing food and veterinarians providing health care. Then they were released a few years back and now repopulate their native range in Mongolia. Are they a reintroduced native species or not? And what is the difference between them and E. caballus in North America, except for the time frame and degree of captivity?

The key element in describing an animal as a native species is (1) where it originated; and (2) whether or not it co-evolved with its habitat. Clearly, E. caballus did both, here in North American. There might be arguments about “breeds,” but there are no scientific grounds for arguments about “species.”

The non-native, feral, and exotic designations given by agencies are not merely reflections of their failure to understand modern science, but also a reflection of their desire to preserve old ways of thinking to keep alive the conflict between a species (wild horses) with no economic value anymore (by law) and the economic value of commercial livestock.

Native status for wild horses would place these animals, under law, within a new category for management considerations. As a form of wildlife, embedded with wildness, ancient behavioral patterns, and the morphology and biology of a sensitive prey species, they may finally be released from the “livestock-gone-loose” appellation.

1 “Horse Evolution” by Kathleen Hunt; Bruce J. MacFadden, Fossil Horses: Systematics, Paleobiology, and Evolution of the Family Equidae (New York: Cambridge University Press, 1992), p. 2052 Patricia Mabee Fazio, “The Fight to Save a Memory: Creation of the Pryor Mountain Wild Horse Range (1968) and Evolving Federal Wild Horse Protection through 1971,” doctoral dissertation, Texas A&M University, College Station, 1995, p. 21.
3 Ann Forsten, 1992. Mitochondrial-DNA timetable and the evolution of Equus: Comparison of molecular and paleontological evidence. Ann. Zool. Fennici 28: 301-309.

4 Carles Vila, Jennifer A. Leonard, Anders Gotherstrom, Stefan Marklund, Kaj Sandberg, Kerstin Liden, Robert K. Wayne, Hans Ellegren. 2001. Widespread origins of domestic horse lineages. Science 291: 474-477.

5 Hofreiter, M., D. Serre, H.N. Poinar, M. Kuch, S. Päbo, S., 2001. Ancient DNA. Nature 2: 353-359.

6 James Dean Feist and Dale R. McCullough. 1976. Behavior patterns and communication in feral horses. Z. Tierpsychol. 41: 367

* Jay F. Kirkpatrick, Director, The Science and Conservation Center, Billings, Montana, holds a Ph.D. in reproductive physiology from the College of Veterinary Medicine at Cornell University. Patricia M. Fazio is a freelance environmental writer and editor, and holds a B.S. in animal husbandry/biology from Cornell University, an M.S. in environmental history from the University of Wyoming, and a Ph.D. in environmental history from Texas A&M University, College Station.

This document is the intellectual property of Drs. Jay F. Kirkpatrick and Patricia M. Fazio. As such, altering of content in any manner is strictly prohibited. However, this statement may be copied and distributed freely in hardcopy, electronic, or Website form. Please include footnotes.

Article first published on in September, 2006.

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  • If they became extinct due to environmental stressors and conditions (which were not man made) and were reintroduced thousands of years later, that would make them “invasive.”

    Add to that, the “mustangs” of today are actually the descendants of herds which were confiscated by the government through the Wild Horse and Burro Act which took advantage of ranchers who were allowing their horses to self-wean. The Act was timed so that it became effective between when most herds had weaned their offspring, and when the ranchers would traditionally gather them to brand. I knew one man who lost over 100 broodmares in this manner. He was not allowed to gather them for five years.

    • Horses and all the other animals that went extinct when humans arrived in North America 12,000 years ago probably were victims of a combination of factors: Warming climate, hunting, diseases introduced by humans and their animals. We will never know for sure but humans appear to have played a large part.

      There is no agreement as to what terms like ‘invasive’ mean, and no logic or science in how we apply them.

      Modern horses seem to be genetically the same as old horses according to DNA analysis. Many animals have been wiped out by humans across our country and then reintroduced. I am speaking of deer, elk, bison, turkey, pronghorn, bighorn and others. No one says these are ‘exotics’ or ‘invasives’. What are the distinctions? What science justifies the distinctions? It is all personal opinion Bob.

      Yes these federal policies are full of perverse actions that are unfair – to Western public lands ranchers in particular.

  • As someone with modest training in biology, I found this article fascinating and convincing. I will now stop using the term “feral” in favor of “re-introduced”.

    But I don’t think that changes much of anything on the ground, and I don’t think it does much to solve the “crux of the (bigger) debate”.

    The current wild horse population in the American west exists in a situation vastly different from 12,000 or a million years ago. A lack of predation (and probably other factors) is allowing population levels to soar, leading to disastrous effect on the rangelands. Emotional affection leads to absolute political protection, regardless of the outcome for the land.

    Regardless of species, breed, or any other designation, population and land degradation is the issue.

    • Yes John you put your finger on the problem which is that there is no way to control horse populations if humans may not reduce horse numbers, given that humans have mostly eradicated horse predators.

      How many horses are too many? Lots more than we have today. Here are interesting horse facts, reported with extensive scientific citations in Dan Flores’ book, American Serengeti: For hundreds of thousands of years before the Pleistocene extinctions, during that period of incredible biodiversity that ended 12,000 years ago when humans arrived in North America, horses represented 25% of the total Great Plains animal biomass. And during the early 1800’s when wild horses briefly reestablished numbers as high as 2-million, horse biomass was around 10% of bison biomass – still only perhaps 1/5th their ancient number.

      The rangelands need keystone grazing species like bison or cows, lots of prey and lots of predators. Pull any of these out and rangelands and wildlife degrade. Put them all back and they recover. Within a healthy system horses would be many times as numerous as today. The crux of the debate I think is whether to restore this system insofar as possible, versus whether to continue ‘management’ practices that attack animal biodiversity by removing cattle, predators, prey – or all three – under various invasive species theories, which for 150 years have only made things worse.

      Many thanks for commenting.

  • Enjoyed the article and use of Dr. Kirkpatrick’s and Dr. Fazio’s writings. May they both rest in peace.

    With finding fossil evidence of horses in North America as recent as 7,500 years ago, the gap is closing. Now knowing they lived into the ice age, suggests just how adaptable they are to climate and other conditions.

    When we think of large mammals dying out, we must also consider what man did in order to survive.

    Did he eat small mammals? What did they eat? What plants did man eat?

    When did he go further northwest and when did he go south/east to warmer climate?

    Why did he migrate? To follow the migration of migratory grazers – it was these animals that kept man alive.

    Therefore, how can it be logical for horses to be an invasive species? Feral simply means there was domestication somewhere in their lineage. And that is not a stretch, knowing that equines were domesticated at least 5,500 years ago.

    Also, legally, there is no distinction between feral and wild. According to the Federal Definition of Livestock, (unless domestic livestock has simply been turned loose from the barnyard), both feral and wild equines are excluded as Livestock because they and their offspring were not domestically bred or raised.

    • Yes Kim, you are correct. There is neither science nor logic in the biological bigotry of ‘invasive species biology’ – the theory which justifies the War on Wildlife including wild horses. Invasive species doctrine is a confused jumble of self-contradicting beliefs which, though taught as science, are about as scientific as the old racial theories that ‘in the day’ were taken for granted.

      Thank you for writing.

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