Over the last several hundred years, humans in North America have unwittingly selected the species that are going to be coexisting with humanity in the future. Rare native flora and fauna have disappeared, but some organisms have flourished in the modified landscape. White-tailed deer, coyotes, black bear, cowbirds, and other familiar (if somewhat “plain”) animals are just a few of the native species that have adapted and even benefited from the presence of people while other species have been driven into extinction.

Some researchers like Paul S. Martin, however, argue that we are living in “a land of ghosts” and that the remaining diversity of wildlife is even more impoverished that it would appear. According to Martin, there should be elephants, sabercats, giant ground sloths, and other creatures still roaming the landscape, and we should try to resurrect the Pleistocene landscape by introducing modern relatives of extinct creatures to North America . The case for such a “re-wilding” is laid out in Martin latest book Twilight of the Mammoths, but I’m not sure that bringing lions & elephants to the American west is prudent, wise, or safe.

A major underlying factor in the re-wilding of America plan is the notion that it’s all our fault; the overkill hypothesis provides the thesis of Martin’s book, and even though he claims that he would be working towards bringing elephants to North America regardless of the reason they became extinct it appears that re-wilding plans are a belated attempt to take responsibility for extinctions that our species played a role in. While I’m somewhat skeptical that the overkill hypothesis provides the primary mechanism for the extinction of North American megafauna around 13,000 years ago, our species certainly hunted animals like Columbian mammoths (Mammuthus columbi) as well as bringing disease and destructive commensals like rats along. I would imagine that the mechanism for the Pleistocene extinctions is far more complex than hunting, disease, climate change, or any other favorite hypothesis can account for alone,* but whatever the mechanism turns out to be the fact of the matter is that there was a catastrophic drop in large-mammal diversity in North America 13,000 years ago.

*Maybe it’s because I’m reading so much about the birth of the sciences of geology & paleontology, but the present debate reminds me of what Cuvier railed against centuries ago. Everyone seems to have their own favorite system or hypothesis of extinction, thus scientific arguments pit system against system, somewhat obscuring the data. Martin’s book is a case in point; those skeptical of the overkill hypothesis are cast in an somewhat unfavorable light, as if they are denying the blatantly obvious or not wanting to take responsibility for modern ecological catastrophe. In Twilight of the Mammoths Martin gives far more leeway to somewhat tenuous evidence that supports his own hypothesis but is much more strict when it comes to the ideas of opponents, and even if he is correct I still get the feeling that presently the system of extinction has become more important than the facts about global extinctions in “near time.”

Enter the re-wilding movement. Martin and others have argued that introducing living relatives (or at least functional equivalents) of extinct Pleistocene creatures would help us better understand what North America 13,000 years ago was like. This may be true to a limited extent, but the heart of the movement involves the creation of “Pleistocene Park” type environments that would increase North American biodiversity and create a new home for creatures under extinction pressures elsewhere in the world. The benefits listed in the article “Restoring Nature’s Backbone,” for example, are primarily scientific; it can be useful to see how tortoises avoid plants that evolved defenses against extinct giant tortoises, but no mention is made of the plants requiring the presence of tortoises to survive or continue their evolution. The primary issue at hand isn’t small-scale research, though, but rather the attempt to modify the landscape to achieve a certain end. There are a number of problems with the abstract plan to recreate a time when mammoths & mastodons roamed the American west, though, and the re-wilding movement has run into some substantial opposition.

One of the primary problems with the re-wilding plan is that it is very abstract, and terms are easily twisted (either in favor of Pleistocene re-wilding or in opposition to it). This weak point is most obviously seen in discussions about brining elephants to North America, specifically where the phrase “free-range” is used.In an American Scientist interview, Martin said the following about introducing elephants to North America;

I would like to see free-ranging elephants in secondary tropical forests of the Americas. Until the end of the Pleistocene, forest and savanna in the New World tropics supported three families of elephants. Observations of free-ranging Indian or African elephants in a reserve of secondary forest should reveal much about fruit dispersal and forest tree ecology under conditions more like those that prevailed before the megafaunal extinctions.

The problem here is that “free-ranging” is not defined; would the elephants go wherever they pleased across the landscape or would they be able to move freely within parks? This is a crucial distinction, especially when the potential destructive powers of elephants outside park boundaries are considered. Presently officials at places like Yellowstone kill bison that wander outside park boundaries, and I would guess that park officials would be even more concerned about African elephants deciding to split the park and take a walk through a nearby suburb. In some articles that I’ve seen by advocates of Pleistocene re-wilding it has been said that the elephants (and other animals) would be kept within fenced boundaries like parks in Africa, but I have yet to come across a more specific plan for these animals.

Likewise, even if electric fences were put up and adequately maintained, escapes and accidents are inevitable, and we should be careful in considering how putting up fences might create boundaries that interfere with the habits (especially migratory routes) of native wildlife. The book Cry of the Kalahari notes the devastating effect of fences on wildebeest in Africa, and more specifically the recent No Way Home notes how animal migrations are being disrupted by a variety of human activities, so erecting fences around a huge swaths of land in North America would create unnatural boundaries that might have harmful effects on native species.

Of further importance is the question of whether introduced exotics will have any positive effect at all; there is also the possibility that simply bringing the “right” organisms back will not have the desired effects. As an abstract to a recent meeting about re-wilding suggested, factors like fires in grasslands may be more important to their health & restoration than the presence of particular herbivores.

The most daunting task facing advocates of re-wilding, however, is the reaction of the public, especially farmers, ranchers, and the general public. It’s hard enough to conserve native predators like wolves, cougars, jaguars, and coyotes; how many ranchers are going to support the presence of lions and cheetahs? Proponents of re-wilding know this is a touchy subject, and it often is pushed to the background. On the Rewilding Institute website, for instance, a lion, a tiger, and a cheetah are featured alongside a cougar, black bear, and other native carnivores. I could find no mention, however, and introducing lions, tigers, or cheetahs to North America on the website, likely because the advocates of such a plan know that the subject is polarizing and given to controversy.

Perhaps the fears of the public could be somewhat assuaged by the assurance that the exotic species would not be given free-reign over the landscape (including suburbs), but a principal dilemma remains. In a recent summary published in Trends in Ecology and Evolution, Tim Caro raises the question of what will happen to the North American landscape when some introduced animals eventually escape into the wild;

Will it be possible to limit adverse biological consequences of inevitable escapes? These include native fauna facing ontogenetically novel predators, fragile vegetation succumbing to new forms of herbivory, and even hybridization between Old and New-World mammals. These hypothetical worries are difficult to resolve in the abstract, but past experience and the precautionary principle suggest that none can be dismissed lightly.

Indeed, Pleistocene re-wilding somewhat hinges upon large predators and herbivores doing what they “should” and not going after cattle, raiding crops, or taking advantage of new situations in a new ecological setting (which they are sure to do). The topic that is often not broached by proponents of Pleistocene re-wilding is that introduced exotics could start interacting with native organisms in novel ways, perhaps out-competing or even extirpating native fauna if not properly controlled. The likelihood of such an event is unknown at present and is probably slim, but it is a question the certainly demands an answer.

Some feel that the objections that the idea has received so far have only been “softballs,” though. In an article that appeared recently in Conservation in Practice, William Stolzenburg accuses critics of Pleistocene re-wilding as missing the point and worrying too much about what exotic species might do to a landscape that re-wilding proponents say is perfectly adapted to species presently living elsewhere. Stolzenburg’s piece is typical of what I’ve seen from the re-wilding proponents, and while it is true that no one is planning on dumping elephants in Arizona just to “see what happens” the ultimate goals of the re-wilding movement cannot be ignored. This isn’t about scientific study on a fenced-in ranch to gain insight; it’s about “resurrection ecology” as a penance for the ecological sins of humans 13,000 years ago.

The re-wilding concept certainly has appeal, though, especially to those who feel that conservation has been too weak and needs a radical new direction. In a Nature article (Donlan 2005) outlining the Pleistocene re-wilding plan (which does mention fenced-in areas to contain the introduced creatures), some of the major proponents behind the idea make an emotional appeal to those concerned with conservation;

We ask of those who find the objections [to Pleistocene re-wilding] compelling, are you content with the negative slant of current conservation philosophy? Will you settle for an American wilderness emptier than it was just 100 centuries ago? Will you risk the extinction of the world’s megafauna should economic, political and climate change prove catastrophic for those populations remaining in Asia and Africa?

Donlan and others might appeal to us to fill up the North American ark with a slew of large species, but there are definitely organisms that are missing. What of the smaller mammals and plants that are also important to ecology? Bringing in equivalents of certain Pleistocene creatures will not create a new “Pleistocene America,” especially since we know that ecologies are complex, integrated relationships between many creatures “great and small.” Rubenstein et al. (2006) notes;

[P]lant communities are dynamic and constantly in flux, genotypically and phenotypically, and there has been over 13,000 years for grassland and shrub-steppe communities to evolve and plant assemblages to change in the absence of the full suite of Pleistocene mega-herbivores.

Indeed, there is an underlying assumption amongst proponents of re-wilding that 13,000 years is not long enough for substantial ecological and evolutionary change to occur, but there is no reason to take such a notion for granted. Plant communities may change even faster than animal communities, and given the fluctuations climate change in beginning to induce we may yet see more rapid change. I haven’t heard of any attempts to restore the plant, insect, or small mammal Pleistocene communities in concert with the introduction of large mammals, nor do I think such a plan would be wise. Just as the large “proxies” for extinct large animals elsewhere have continued to evolve, so have the ecologies of North America, thus making the continent even more divergent from the Pleistocene than supposed.

Simply put, Pleistocene re-wilding would not restore or resurrect a lost ecology; the plan is to patch one together using existing proxies to (at best) approximate lost ecologies. The Pleistocene creatures, from the dire wolf to the Columbian mammoth, are forever lost. An African elephant is not a mammoth, a black rhinoceros is not a giant ground sloth, and a modern day cheetah is not its extinct relative (cougars, in fact, are probably more closely related). As stated in Rubenstein, et al. 2006;

Indeed, rather than restoring our ”contemporary” wild ecosystems to the ”historic” wild ecosystems of the Pleistocene and their original levels of ecosystem functioning, which are unknown, Pleistocene re-wilding could instead result in ”re-wilded” novel, or emerging, ecosystems with unique species compositions and new or altered levels of ecosystem functioning… Biogeographic assemblages and evolutionary lineages would be co-mingled in novel ways; new parasites and diseases could be introduced … and food chains would be disrupted. Moreover, without really knowing how Pleistocene ecosystems functioned, there will be no way to determine whether Pleistocene re-wilding restored ancient ecosystems or disrupted contemporary ones.

[ "..." denotes references removed from original text for ease of reading.]

The authors of Rubenstein et al. 2006 continue;

We all remember ”Jurassic Park”, Crichton’s (1990) fictional account of re-wilding an isolated island with extinct dinosaurs recreated from ancient DNA. Pleistocene re-wilding of North America is only a slightly less sensational proposal. It is a little like proposing that two wrongs somehow will make a right: both the modern-day proxy species are ”wrong” (i.e., different genetically from the species that occurred in North
America during the Pleistocene), and the ecosystems into which they are to be reintroduced are ”wrong” (i.e., different in composition from the Pleistocene ecosystems, as well as from those in which the modern-day proxy species evolved). Pleistocene re-wilding of North America will not restore evolutionary potential of North America’s extinct megafauna because the species in question are evolutionarily distinct, nor will it restore ecological potential of North America’s modern ecosystems because they have continued to evolve over the past 13,000 years. In addition, there is a third and potentially greater ”wrong” proposed: adding these exotic species to current ecological communities could potentially devastate populations of indigenous, native animals and plants.

This is assuming the re-wilding may take place and be successful, of course, and not all the proposed transplants will take. Prior to 1900 (around the time of the Civil War) dromedary camels were introduced to the American southwest for use as pack animals. The camels did not do well in their new home, and the feral individuals there perished. In Australia, though, the same species did take hold and has devastated some native floras, and so we should not expect introduced camels to always do what we would like in terms of conservation. Disease is another important question, both in terms of introduced animals spreading disease or succumbing to it, especially in the case of the cheetah. Cheetahs are already suffering from an inbred population susceptible to disease; if left to roam free, would an introduced population soon die out in the presence of unfamiliar diseases?

Indeed, while I certainly do not agree with the views of people who would like to see every wolf, cougar, coyote, hawk, and bear shot in order to crush wilderness under the heel of humanity, I see little behind introducing African species to North America simply because we think it’d be interesting to have them here. It certainly would be amazing to see a cheetah run down a pronghorn, but this would be a forced hunt, something that is artificial despite claims to naturalness. No matter what the reason for their extinction, trying to replace the North American megafauna of times past is a time to integrate species adapted to other environments into our own as if the Pleistocene extinctions did not occur. The idea that such introductions will help the evolution of endemic species is sometimes proffered but absurd; “help” evolution to do what? Ecologies have been changing since the Pleistocene and will continue to do so as anthropogenic climate change continues, so even if we let elephants mingle with bison there would be no guarantee that the reintroduction would take as “wild” places continue to dwindle and are presently in a state of climate-driven flux.

What North American wildlife most needs right now is a more rigorous and responsible conservation & management plan, especially for carnivores like cougars and jaguars that are actively trying to reclaim their former ranges without the intervention of humans (thus far). The return of wolves to Yellowstone was a good start, but it can’t be the end of restoration work sorely needed in North America. Creating corridors for wildlife to pass through and making sure migration routes are undisturbed are also top priorities, the cutting of habitats into isolated patches being a prelude to extinction, and I fear that attempts to create a Pleistocene America would take away from these efforts. Lets make sure that native animals are not only surviving but thriving before we even contemplate the notion of bringing in alien species to make ourselves feel better.

In Twilight of the Mammoths, there is a particular part of the book where Martin says cryptozoologists looking for living giant sloths are holding out hope for something they’ll never find. Oddly enough, Martin is making the same error in hoping for a return of Pleistocene America. It was lost long before he or I was born and cannot be reclaimed, and any effort to do so would merely be putting together an unnatural assemblage of animals in the hopes that nature would heal itself. We’ve long passed that point. As Stephen Meyer wrote in The End of the Wild;

Since the invention of the first stone tool, humanity has pounded the wild into a shape that fits its needs. Forests are transformed to fields. Swamps are drained. Arid landscapes are irrigated. Mountains are flattened and valleys filled. The bounty of nature in converted into commodities: timber, food, luxuries. Coexisting with nature has always meant taming it – consuming it. As the human population jumped into the billions the rise of human selection as the dominant evolutionary force was inevitable, and so was the end of the wild.

We are now at a point where we are actively choosing our ecological companions in the future, and trying to return to the Pleistocene while the world continues on based upon the contingencies of history would result in pulling ecologies in two different directions. The North American megafauna is gone, but large mammals still remain here and will continue to evolve as they always have. Perhaps some (or even many) will become extinct eventually, and as much as that saddens me nature will continue and new forms will evolve to fill open niches even if no one is around to see it. Conservation and preservation are of the utmost important for a number of reasons ranging from aesthetic to economic, but trying to breathe life into a long-gone past is not an appropriate way to try and turn the tide of ecological destruction.


Caro, T. (2007) “The Pleistocene re-wilding gambit.Trends in Ecology & Evolution.
Vol. 22 (6), June 2007, pp. 281-283

Donlan, J. (2005) “Re-wilding North America.Nature. Vol. 436, pp. 913-914

Rubenstein, D.R.; Rubenstein, D.I.; Sherman, P.W.; Gavin, T.A. (2006) “Pleistocene Park: Does re-wilding North America represent sound conservation for the 21st century?.” Biological Conservation. Vol.132, pp. 232-238

Stolzenburg, W. (2006) “Where the Wild Things Were.Conservation in Practice. Vol. 7 (1), pp. 28-33


  1. #1 derek
    February 18, 2008

    That article you cite quotes “It is not restoration to introduce animals that were never here,” said University of Washington anthropologist Donald K. Grayson, “Why introduce Old World camels and lions when there are North American species that could benefit from the same kind of effort?”

    What on Earth is an “Old World” camel? Camels are New World animals.

  2. #2 Greg Laden
    February 18, 2008

    I totally agree that we should develop clones of 12-20 Pleistocene megafuana, including elephants and predators, and release them in Canada and Nebraska and parts of Wyoming. But only because it would be kick-ass cool.

    I have read on and closely followed this debate (causes of extinction) since way back. I have a pre-publication copy of Martin’s book Quaternary Extinctions” and everything. Lately, my interest has been invigorated because a loved one is engaged in related field work and I am reliving some of the thrill vicariously.

    I am totally agnostic as to the reality of the situation. What happened happened, and we want to know, but there is no guiding philosophical principle. Or even principal. Whichever applies.

    Here, though, is a conundrum: So we want to resurrect the species we made extinct because our landscape is full of ghosts, right? But isn’t the landscape full of Pleistocene Ghosts?

    Well, every single one of the last five or six glacial cycles saw the extinction of an approximately similar sized “handful” of large mammals. But humans were only around for the last one or two.

    So, do re reconstitute (for rewilding purposes) only the ones that disappeared during the LGM? Wasn’t the period prior to the LGM also a ghost-inhabited landscape from the broader Pleistocene perspective?

    I agree with P.M. Cloned them all and set them free! Oh I’ve got to go now, need to finish working on my model railroad set in the basement….

  3. #3 Brian Schmidt
    February 18, 2008

    “Well, every single one of the last five or six glacial cycles saw the extinction of an approximately similar sized “handful” of large mammals.”

    I’m not aware of that – I thought the last extinctions were unique. Do you have a cite?

    The key problem as I understand for non-anthropogenic causes of Pleistocene extinctions is that only large mammals died out, and not small ones. No other theory has a good explanation for this.

  4. #4 tai haku
    February 19, 2008

    Nice to see a few new links and ideas for me to explore in relation to what is as Greg points out a kick-ass idea. I suspect wholly impractical rather like rebuilding a game of jenga into its end position from the fallen bricks using some other bricks that aren’t quite the same and then trying to play on.

    Also a) the rewilding institute sends out some of the densest hardest to read stuff on their blog, and b) Bactrian camels are old world Derek n’est-ce pas? I think they are talking about big camelids as opposed to guanacos and stuff.

  5. #5 Maureen Lycaon
    February 19, 2008

    Brian Schmidt — Chasmaporthetes (the so-called “hunting hyena”) only became extinct in NA during the second major glaciation. It survived the first one in a refugium in the region of Floria. My knowledge of earlier Pleistocene mammals is very rusty now, but checking out Pleistocene Mammals of North America should give you some more species.

    It is my understanding as well that few or no small mammals became extinct at the end of the Pleistocene in North America.