Every now and then, news crops up of attempts to clone a mammoth or other now-extinct species. While there certainly are things we can learn from such processes, they almost seem to have more to do with penance or (in the case of mammoths, at least) the desire to see and study a magnificent animal now lost. Especially since Jurassic Park hit it big over a decade ago, people have been wondering if it is at all possible to bring back long-extinct animals for study (and just as likely, profit). Jeremy of The Voltage Gate, however, alerts us to a more ecologically-based attempt to restore a “lost world”; the introduction of modern-day analogues to extinct creatures like lions and mammoths to North America.
In an open-access commentary published to PLoS Biology last year, Henry Nicholls describes the hypothesis of some conservation ecologists that “re-wilding” (a word that, to me, has the some pseudo-linguistic flavor of “signage” and “we-ness”) North American with extant species analogous to those that went extinct during the Pleistocene would be a boon for the environment. From the article;
Rather than trying to simply ring-fence what wildlife remains, conservationists need to be restoring whole ecologies to something of their former glory, says Josh Donlan, an ecologist at Cornell University (Ithaca, New York, United States). Last year, he and a long list of high-profile conservation biologists penned a controversial commentary in Nature in which they laid out the case for rewilding North America—seeding the continent with suitable stand-ins for species that went extinct thousands of years ago.
Donlan’s world would see carefully chosen slivers of North America grazed by giant tortoises, horses, and camels; the stamping ground of elephants in place of five species of mammoth; and African lions in lieu of the extinct American lion that once stalked the continent.
The benefits, they argued, are obvious. It would restore ecological processes that have gone by the wayside, mend broken evolutionary relationships, create a back-up population of some of the planet’s most endangered species, and raise huge awareness for the conservation cause. “The obstacles are substantial and the risks are not trivial, but we can no longer accept a hands-off approach to wilderness preservation,” they wrote of their optimistic vision.
I agree that merely trying to create pockets of wilderness will not work; as I discussed during a discussion of current endangered species, we would do well to remember that although the heath hen seemed to rally its numbers in Martha’s Vineyard so long ago, a lack of diversity, disease, and other unfortunate circumstances caused the species to become extinct. Simply creating a pocket of land for a species to reside in, and in some ways may imperil a species more than if the same number of members of a population were more spread out. David Quammen puts it more eloquently in this excerpt from his book Song of the Dodo;
Let’s start by imagining a fine Persian carpet and a hunting knife. The carpet is twelve feet by eighteen, say. That gives us 216 square feet of continuous woven material. Is the knife razor sharp? If not, we hone it. We set about cutting the carpet into thirty-six equal pieces, total them up–and find that, lo, there’s still nearly 216 square feet of recognizably carpet like stuff. But what does it amount to? Have we got thirty-six nice Persian throw rugs? No. All we’re left with is three dozen ragged fragments, each one worthless and commencing to come apart.
If we are to take an active role in conservation, wildlife corridors need to be established and the idea that one large national park is enough to preserve a species must be dismissed. In fact, many “problem” species like black bears, coyotes, and white-tailed deer are doing so well because they do not require pristine habitat; they easily extended their ranges into urban and suburban areas, and as such will likely be with us for a long time to come.
So what of attempts to create “Pleistocene Parks” in different areas of the world? While restoring habitats destroyed or altered by recent human activity (i.e. the building of a dam) is reasonable and admirable, I feel that if Donlan and others expect to release elephants and lions in North America they are certainly misguided. Rather than attempting to create essential corridors to protect species already present and in need of assistance (the elusive jaguar, which is seen every now and again in the American southwest, being the one that most immediately springs to mind), those in support of Donlan’s plan would essentially be trying to exercise penance for the “sins” of early American inhabitants during the Late Pleistocene Extinctions.
Indeed, the PLoS article seems to throw in with the “Overkill Hypothesis”, a view that has been hotly debated for decades. Originally espoused by Paul S. Martin, this view currently holds that human predation on herbivores (i.e. mammoths) not only caused the extinction of the prey animals but also predators that relied on the herbivores for food. Sometimes evidence for mammoths being stampeded off cliffs is used to support this view, but it does have some substantial problems. In addition to “prey” species, giant sloths, glyptodonts, and others that were not likely often on the menu did go extinct, while species that were almost certainly hunted (like bison) did not go extinct. Indeed, humans would have to have been pretty hungry (or wasteful or homicidal) to kill off enough large herbivores to cause their extinction, but again this leaves the question of why large, dangerous species like mammoths went extinct and easier prey like bison did not.
Overkill is not the only hypothesis to take some prominence, however. Effects of climatic changes and the potential for a hypderdisease are often cited as playing a part (if not being the major factor) in extinctions. These ideas are not without problems of their own, however; the climate does not appear to have changed dramatically enough to cause the extinction of so many placental mammals, and it’s hard to conjure up a disease that is so non-specific that it would cause the extinction of a wide diversity of large mammals, yet leave humans and some others standing. There has been some evidence for disease among some large animals, however; signs of tuberculosis (a disease that does affect bone) were found in 59 of 113 mastodons (52%), a shorter relative of the more famous mammoths. This is not the “smoking gun” to the case but it does give us an important clue about what was happening during this critical time, and I would guess that in the end it will be a combination of factors that caused the Pleistocene extinctions, not climate, disease, or predation on their own. Even so, being that disease and hunting both seem to be important factors we can’t with good conscience say that humans had nothing to do with the extinctions, especially since it seems to be correlated with our arrival in North America. The answer remains elusive, but it would not be inappropriate to ask the question “Should we try to recreate what we had a hand in destroying?”
Personally I don’t think the introduction of large foreign species (which would be deemed invasive if they gained a foothold on their own) is a particularly good idea. All across America, wildlife is making a comeback, and I can only imagine the phone calls animal control would get if elephants were walking down Main St. or lions were nosing through the trash. How would these animals be kept from migrating or trying to cross freeways? If we fence them in we have done nothing more than make a huge zoo, the fences hampering the migration of endemic species. On top of that, you would merely have islands of introduced predators and prey, exactly the opposite of what we should try and establish. What Donlan seems not have considered is that we do in fact have predators and herbivores already living in North America, wolves, mountain lions, bears, deer, bison, moose, and others already calling our section of the globe home. Why should we try and introduce animals adapted to deserts, swamps, and savanna to the American plains when we already have creatures in need of our assistance?
The introduced animals would not merely “play nice” with existing organisms and have no impact on endemic species; is it possible that if we introduced lions, we would lose the already imperiled Grey Wolf? Would elephants find enough food and how would they affect buffalo populations? What about disease? Could American species be affected by diseases carried over from Africa, India, and elsewhere? It seems all too easy to forget that when you take a species from one area and move it elsewhere, disease usually follows with disastrous consequences.
I wish I could be kinder to proponents of the “Pleistocene Park” view, but ultimately I think the endeavor is foolish and will do far more harm than good. It is far too late to attempt to make reparations for an extinction triggered thousands of years ago, and the focus should be on preservation of habitat and habitat corridors rather then trying to recreate what existed at the end of the last Ice Age. If conservation ecologists wish to restore habitat destroyed by industrial development, by all means they are welcome to do so and I think it’s an honorable endeavor, but we can not turn back the clock to the Pleistocene.
Update: Well wouldn’t you know it; the new issue of the journal Nature features an article about a potential cause for the Pleistocene extinction not mentioned in my initial post; the impact of a comet or asteroid. I know some of you must be thinking “Oh no, here we go again with the impacts and ‘Nemesis’ business,” but according to the article there seems to be a fair amount of evidence (much like what clued scientists off to the K/T impact) for such a collision, and on May 24th scientists will be getting together to discuss the findings. The following evidence is presented in the article;
The new evidence comes in the form of geochemical analysis of sedimentary layers at 25 archaeological sites across North America… Certain features of the layers, say the team, suggest that they contain debris formed by an extraterrestrial impact. These include spherules of glass and carbon, and amounts of the element iridium said to be too high to have originated on Earth. In addition, the rocks contain black layers of carbonized material, which the team says are the remains of wildfires that swept across the continent after the impact.
Indeed, this seems fairly good evidence to suspect that an impact occurred, but the real question is how far-reaching were its effects? Much like what was done with the study of the K/T boundary, geologic sites from the same time period in various locations in North America would have to be sampled for the presence of iridium, glass/carbon spherules, or bands of carbon laid down in the wake of wide-ranging forest fires. If it could be established when and where this catastrophe occurred (which could prove difficult if it was a comet or an asteroid that exploded before actually hitting the earth’s crust) it could very well give us a crucial piece of evidence as to why the Late Pleistocene extinction occurred. If such evidence were found, we would then be able to recognize that changes in climate, disease, predation, and an extraterrestrial impact together put so much pressure on North American species that a wide diversity became extinct, reflecting what I call the “Really Bad Day hypothesis.” It may sound somewhat childish, but it appears that on both large (i.e. extinction of non-avian dinosaurs) and small (i.e. the heath hen) scales, a streak of “bad luck” can be absolutely devastating to organisms, and it is foolish to look for only one answer to the disappearance of so many species in so short a time. Instead we should look for similar patterns; changes in temperature married with changes in migration (and hence migration of disease) as well as possibly unaccounted for catastrophic factors like asteroid impact. As other paleontologists before me have noted, uniformitarianism was a great step forward in scientific thought when it first was espoused and became accepted, but it can also act as an intellectual straightjacket; it’s hard to consider the impact of a massive asteroid or dramatic climate change as drivers for extinction when we have not encountered either in recorded history. Hopefully new information will be forthcoming and scientists will be open to the possibility of a Late Pleistocene impact (even if it ends up being less dramatic than hoped); I would hate to see another chapter in paleontology where geologists and paleontologists (and now, archaeologists and anthropologists) end up being cranky at each other rather than collaborating.