This new article in the Wall Street Journal by Stephanie Simon has gotten many people talking about wild horse issues, including the issue of whether or not wild horses are “feral” and deserving to be eradicated from our public lands, or a returned native species. Ross MacPhee, Ph.D. from the American Museum of National History has been kind enough to allow me to reprint his response to Ms. Simon, and it is the best explanation I have heard regarding the wild horse’s evolution.
“Mustang Plan Riles the West”
BY STEPHANIE SIMON
Federal wildlife managers are fighting in court to take the unprecedented step of castrating 200 wild stallions in Nevada, in an effort to control surging populations of wild horses across the West.
Animal-rights activists oppose the plan, which they contend would strip the wild stallions of their fighting spirit and change herd dynamics. A coalition of horse advocates last month filed suit to block the U.S. Bureau of Land Management from castrating the stallions, also known as gelding. In response, the agency agreed to postpone the castration until a federal court in Washington, D.C., can hear arguments later this year.
Wild horses are not native to America; they are descended from domesticated horses brought over by early European explorers. Still, federal law protects mustangs as “living symbols of the historic and pioneer spirit of the West.”
Here is the response:
Dear Ms. Simon,
I am writing to briefly comment on your WSJ article on wild horse castration, but only with regard to a particular scientific issue: the “native” or “endemic” vs. “alien” or “invasive” status of wild horses in North America. Although these terms are used in different ways by different people or interest groups, I’ll stick with an evolutionary definition of a “native” species as being one that differentiated or diverged from its immediate ancestor species within a specific geographical locale.
In my view, the primary considerations are these:
1. It is correct that the standing crop of wild horses in the US is recently derived from lines domesticated in Europe (and Asia).
2. But those lines themselves go much further back in time, and converge on populations that lived in North America during the latter part of the Pleistocene (2.5M to 10k years ago). The evidence for this, until recently, has been primarily morphological, based on comparisons of living vs. fossil horses. The genetic evidence from ancient DNA is still preliminary, but it seems to point to the same conclusion, which is that the species Equus caballus–the species encompassing all domestic horses and their wild progenitors–arose on this continent.
3. The evidence thus favors the view that this species is “native” to North America, given any rational understanding of the term “native”. By contrast, there are no paleontological or genetic grounds for concluding that it is native to any other continent.
4. From a scientific standpoint, it is completely irrelevant that native horses died out in North America 10,000 years ago, or that later populations were domesticated in central Asia 6000 years ago. Such considerations have no bearing on their status as having originated on this continent.
5. It is worth noting that dozens of other species in addition to native horses died out at the close of the Pleistocene, in an episode termed the megafaunal extinctions. The only major difference is that, long before 10,000 bp, E. caballus had established itself on other continents (South America as well as Eurasia) by crossing landbridges. There they survived. Reintroduction to North America 500 years ago is, biologically, a non-event: horses were merely returned to part of their former native range, where they have since prospered because ecologically they never left.
5. Whether these considerations should play a role in policy decisions I leave to others. At the same time, it needs to be more widely understood that the horse’s status as a native North American species is beyond serious question, whatever side of the debate over wild horse control one leans toward.
Ross MacPhee, PhD
Division of Vertebrate Zoology
American Museum of Natural History
New York NY 10024