Wild
Horses as Native North American Wildlife
By Jay F. Kirkpatrick,
Ph.D. and Patricia M. Fazio, Ph.D.*
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 2-3 million years ago
and a possible origin at about 3.4-3.9 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.
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’ 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.
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. 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.
According to the work of Uppsala University researcher
Ann Forstén, of the Department of Evolutionary Biology, the date of
origin, based on mutation rates for mitochondrial-DNA, for E. caballus,
is set at approximately 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 Vilà, also of the Department of Evolutionary
Biology at Uppsala University, has corroborated Forstén’s work. Vilà 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.
Finally, the work of Hofreiter et al,
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.
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.
_________________________________
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 currently a freelance environmental writer and editor
residing in Cody, Wyoming 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.
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(Distributed March 2, 2005)
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Ω
Please note:
This document is the sole 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 (March 2, 2005).
