Inheritors of the Earth

by Chris D. Thomas

  One thinker in this area is Josh Donlan, from an organization known as Advanced Conservation Strategies, who has come up with a vision for North America and, by extension, the world. He wants to create big, wild spaces containing big, wild animals. That is conventional enough. The unconventional part is to identify ecologically similar relatives of the bitumen-preserved animals from California’s La Brea tar pits and release them in North America. Mastodons, large-headed llamas and American lions may have shuffled off this mortal coil, but we could always replace them by Old World elephants, South American llamas and African lions.15 Cheetahs could be introduced to pursue native pronghorn antelope in the absence of the original fast-running relatives of pumas that used to populate the plains. Donlan and his collaborators have suggested that having this international cast of animals roaming the wilds would improve the prospects for North American plants, which evolved in the presence of large grazing animals. The flora might be expected to survive better if large animals are returned, with the aspiration that all the native insects that feed on the plants would then prosper, too, and the lizards and birds that feed on insects would thrive in turn.

  This is an intriguing idea, but it is perhaps unfortunate that the originators of the idea called the proposal ‘Pleistocene rewilding’. The Pleistocene is the geological epoch that covered the last two and a half million years of sporadic ice ages (until 11,700 years ago), so this implies a return to the past. Rewilding (as opposed to wilding) directly conjures up the expectation that we are returning to a more pristine past, to an older baseline, rather than starting off in a new direction. Whatever happens, and however many different species are released, it will not create a facsimile of the past because North America’s vegetation has already developed for ten thousand years in the presence of humans and the absence of the extinct animals–and the replacement animals are not exactly the same species as those that became extinct. Vast ground sloths and sabre-toothed Smilodon cats have no modern equivalents that are available to release.

  Europe is much the same. Twenty-first-century Europe lacks rhinoceros, hippos and elephants because our ancestors killed them all. We could release their nearest living relatives: Mediterranean shrublands could become the refuge of African black rhinoceros; while great one-horned rhinos from India and Nepal and African hippos could find security alongside white horses and black bulls in the wetlands of France’s Camargue. Again, great fun, but not what it once was. The past has gone, and who is to say that the future impacts of an international medley of imported creatures in Europe and North America, or anywhere else in the world, would be fundamentally that different from using feral sheep, cows, donkeys and horses? However, it is well worth exploring. The greatest contribution of these ideas is to expand our ambitions beyond conventional conservation, which sometimes feels akin to fiddling while Rome burns. We can think about engineering new ecosystems and biological communities into existence, inspired but not constrained by the past.

  Debate about such proposals tends to dwell on three areas of concern. Is it natural? The answer to this question is yes, as I discussed already. Is it practical? There are inevitably great challenges, and the legislative barrier to releasing lions (which will eventually kill some people as well as livestock, even if it is only a few) in North America might be insurmountable. However, it is practical in some locations, at least on private ranches with adequate fencing, although this rather goes against the grain for the originators of the idea, who are dreaming of a magnificent, wilder landscape. Is it better or worse for American biodiversity? This last question is clearly unanswerable. None of the possible future states of the world will be fundamentally better or worse than the world’s pre-human condition. They will just be different.

  So we need to define ‘better’ as a human preference. Unfortunately, there is no consensus of what ‘better’ should be. If you accept my argument that we should minimize the number of species that become extinct because some may turn out to be important in future, then ‘better’ in the case of releasing rhinoceros species in Europe would not be that European ecosystems are somehow yearning to have rhinos bumbling around in them but that the grazing and browsing they provide might possibly save some Mediterranean plants and insects from extinction. This may be so, but there is no evidence one way or the other–although it could be ascertained by experiment. The more tangible benefit is that rhinos are endangered elsewhere. We could stop them from going extinct, just as Javan elephants have survived because they were transported to Borneo. But if this is the logic, why stop there? If black rhinos are worthy of being saved, why not mammoths?

  ‘De-extinction’, or resurrection biology, is a term that is increasingly used by scientists and conservationists to describe exactly this, the latest fad in affirmative action–more brave thinking. If currently rare animals and plants might in future become more abundant and widespread, why should this privilege not be extended to species that have recently become extinct? So far, it has been attempted in earnest only for the extinct Pyrenean ibex, a subspecies of Spanish ibex, albeit without success. Genetic material from Celia, the last living female, was injected into a domestic goat’s egg, stimulated to start growing, and then implanted back into a surrogate goat mother. Despite many attempts, however, all the embryos died before birth, except for one kid that had a deformed lung and perished a few minutes after it was born. Even if a Celia II could be created (in principle, it should be possible), there are still no males, so we are a long way from re-creating a viable population. Maybe it would be simpler to let Celia rest in peace and release other kinds of ibex instead–different Spanish ibex subspecies are still available. Taking inspiration from the Bornean elephants and Donlan’s ideas, and marrying this up with a strategy to save as many different species on Noah’s Earth as possible, a more adventurous strategy would be to release the closely related and highly endangered walia ibex, which is down to a remnant population of about five hundred individuals in the mountains of Ethiopia. That would be a greater contribution to global conservation.

  The next ‘big prize’ in resurrection biology is the woolly mammoth. Several research groups are attempting to bring mammoths back by cloning their permafrost-preserved genes, or by splicing mammoth-like genes (which govern the appearance and particular physiological attributes of mammoths) into Indian elephants to create chimeric elemoths or mamphants. I very much look forward to seeing them; but we should not kid ourselves that mamphants are woolly mammoths. They are hybrids, made in a laboratory–although I do not personally have a problem with this. If we can protect these animals from our traps and guns, and eliminate the trade in ivory (or grow ivory in vats), there is no reason why mamphants could not ‘look forward’ to a long future of evolutionary success. Knitting the genes of different species together might also work if we wish to breathe life into animals that resemble (but are not the same as) any of the other 177 human-killed large mammals that have died out in the last fifty thousand years but whose ancient DNA is considerably more damaged (not having been frozen) than that of the mammoth. Bison bounced back with a few cow genes on board. Why not animals that are quite like large-headed llamas, if their genes can be dug up from somewhere and spliced into Asian camels?

  If this were to happen, and it surely will for at least a few of the extinct species, these spliced-together creatures will represent novel hybrids–biological gains–that may or may not turn out to be successful. They will be similar in this respect to other hybrids that have come into existence in the Anthropocene, such as honeysuckle flies, Italian sparrows and Oxford ragwort, which are successful, or Yorkwort, which is teetering on the brink of extinction a few decades after it originated. To all intents and purposes, we will be creating new hybrid species. This would be an interesting precedent. Although we have repeatedly hybridized domestic animals and, particularly, crop plants for use in agriculture, it would be something of a new step if we are deliberately to create new hybrids and then release them into the wild.


  This leads to the next question. Why should we do this only when one of the parent species happens to be extinct? If an elemoth is to be created from one living (Indian elephant) and one extinct (mammoth) ancestor, why not create novel entities from two or more living species (or two or more extinct species)? If the goal is to have a relative of llamas and camels roaming the Great Basin, and for those animals to be unique to North America (as large-headed llamas were), I see no particular reason why inserting a few large-headed llama genes into camels or guanacos is a better option than creating a population of camas, which are hybrids between camels and South American llamas–the domesticated relatives of wild guanacos. Camas would contain the surviving gene pool of the camel relatives that first originated in North America.

  The purpose of this discussion is not to advocate or dismiss any one or another of these specific ideas but to recognize that, if we regard all human actions as natural, and thus legitimate options, we can use technologies and contemplate strategies to maintain and increase biological diversity in a variety of ways that ecologists and conservationists would regard as unconventional–and which would historically have been regarded as unacceptable. Aiming to increase biological diversity is just as legitimate as attempting to reduce the rate at which (existing) diversity declines. In the case of mammals in North America, we could adopt some combination of strategies: release ecologically similar species from different continents, release endangered species from elsewhere in the world, import threatened species from Central America as the climate warms, re-create nearly ‘pure’ forms of a few extinct species, genetically splice ancient DNA and living species together, generate new hybrids by conventional breeding (as in my ‘cama’ suggestion, and the now vilified beefalo hybrids between cattle and bison), use domesticated animals to graze and browse, or just leave wild deer and feral pigs to get on with it, and allow grizzlies and wolves to recolonize from the north, as they already are.

  The conservation rationale for each of these approaches is usually stated to be some combination of making the world more natural (which is fallacious) and restoring it to a state that resembles one that existed in the past (which is equally fallacious). None of these options will cause the biological world to revert to its original trajectory. However, we should not exclude any option simply because it is novel. It is up to us to decide whether we wish to intervene and, if so, how. Any such decisions, including the decision not to act at all, will simply set the world going in a slightly different but equally natural direction.

  Back in Monterey, it is again possible to take in the bizarre sight of America’s most famous butterfly surviving the winter by clinging to the pendulous twigs and leaves of an Australian gum tree. Beside it grows a rare native Californian tree that is now a mainstay of the southern hemisphere’s forestry industry. The Monterey pine is saved, even if its eventual survival may depend on populations that have gone wild in South Africa. No, this is not how nature used to be before humans came along. But we did, and this is the new natural world. Species survive where they can, thrive where they can, and are used by humans where we are able to use them.

  California now supports well over a thousand species of introduced plants and, although the ice age giants that lie preserved in the tar pits at La Brea are gone, the last few hundred years has seen the addition of European rabbits, two species of squirrel, house mouse, two rats, Barbary sheep, fallow deer, wild boar, pheasant, turkey, starling, house sparrow, brown-headed cowbird and numerous insects and slugs, as well as all our domestic animals. Like the star-thistles that are already on their way to becoming new species that live only in California, all these introduced plants and animals will begin to diverge from their ancestors which still live in other parts of the world, and eventually increase rather than decrease the variety of life on Earth. It is not necessarily a tragedy for the biological diversity of California, or for our planet as a whole. We should still try to save species that live only in California, but waging war on interlopers is unlikely to be important except in situations where they specifically endanger other species. Even then, it is worth the fight only if a permanent solution is available.

  Whenever our urge is to fight a specific biological change, we should ask the following triplet of questions. Will our efforts have made much difference a few hundred years hence? If not, this means we are fighting a battle we will inevitably lose. Next, will our great-grandchildren’s great-grandchildren be that bothered if the state of the world has been altered, given that they will not know exactly how it is today? If the answer to this second question is no, this means we are fighting battles we do not need to win. If change is inevitable, which it is, we should then ask a third question: how can we maximize the benefits that our descendants derive from the natural world? In other words, how can we promote changes that might be favourable to the future human condition, as well as avoid the losses of species that might be important in unknown ways in future?

  If we can create new biological success stories by whatever means, let’s do it. We can protect animals and plants in places where it is feasible to do so, rather than where they came from. We can transport climate-threatened species to places they could not otherwise reach–why not, if this increases the chances that individual species will survive? We can import species into ecosystems where they did not previously occur, for example if drought-resistant trees could increase the resilience of a forest to future water shortages. We can introduce species to new geographic regions so as to increase the impoverished diversity of human-created habitats. We can foster novel ecosystems that contain mixtures of species never seen before. We can deliberately create ecologically diverse landscapes that are mosaics of different kinds of ecosystem, richer in species than most that exist today. We can also help direct the evolutionary process: establish new hybrids that will perform ecological functions we find useful, develop new forms of insects that will eat pestilential weeds, and use genetic modification technologies to insert disease-resistance genes into captive frogs so that they can repopulate South America. It is time for the conservation and environmental movement to shed its self-imposed restraints and fear of change and go on the offensive.

  Welcome to Anthropocene Park. Our home.

  Epilogue

  One million years AD

  Surprising as it might seem, it is entirely possible that the long-term consequence of the evolution of Homo sapiens will be to increase the number of species on the Earth’s land surface.1 Of course, it is impossible to anticipate what might happen in the future. Humans may become extinct as the result of an event so catastrophic–for example, an extended nuclear winter, or the biological collapse of the planet associated with artificial life–that all bets are off. And who can guess what will unfold if humans or our bio-mechanical upgrades survive the next million years and develop currently unimaginable technologies? However, if we extrapolate from the biological processes that we do know about and ignore the world of unknown unknowns, it is at least possible to contemplate the impact of humanity on life on Earth a million years hence.

  Consider the losses first. We have already extinguished most of the largest land mammals, and we have removed most of the flightless and disease-susceptible birds that used to live on isolated islands. Other island species that are unable to survive in the presence of continental species are also on the way out. In future, additional mammals, birds, reptiles, fish and plants may also be hunted, fished or picked to extinction. Some localized parts of the world will lose many of their unique species if they become so heavily populated or cultivated that humans remove almost all vestiges of the former vegetation. Many high-mountain species will disappear as the climate warms. Undoubtedly, there will also be losses that we cannot anticipate.

  How much will all this extinction come to? Heading the list so far are the birds, which have already lost around 9 per cent of the species that used to exist, most of which were former inhabitants of oceanic islands. Additional species will have been lost
without trace. This is not typical, as far as we know, but it is possible that Pacific land snails and some groups of insects will have suffered as much. However, when it comes to vertebrate extinctions so far, it seems that birds are top of the list (amphibians may catch up). At the current rate of extinction, we can expect another 12 per cent of the world’s bird species to disappear in the next thousand years of human existence.2 The overall average extinction rate (not just for birds) seems to be heading towards the loss of around 10 per cent of species in a thousand years, which falls far below the level of extinction (75 per cent plus) required to match one of the previous ‘Big Five’ mass extinctions in the geological past. However, the Anthropocene would qualify as the ‘Big Sixth’ if the current rate of extinction keeps up for the next ten thousand years, which is a very short time in the history of life.

  Declaring the Anthropocene to be the sixth mass extinction is somewhat premature. Nonetheless, a quarter of mammals, a third of cacti and reef-forming corals, and two out of every five amphibians are listed as being threatened in some way.3 They will not all die out, but some threats are likely to escalate in the near future, such as human-caused climate change and more intensive use of the land linked to the human population. So, based on recent rates of extinction and projected threats, we could guess that human-linked extinctions will end up in the ball park of 20–40 per cent in the next thousand years–for most kinds of animals and plants. That might be about it, however, for two reasons. First: species that are particularly sensitive to human disturbance and to human-assisted biological invasions are progressively disappearing, leaving the more robust and widespread animals and plants to survive. As we have seen, continental species are surviving relatively well, and most basic types of familiar animals, plants, fungi and microbes are coming through the Anthropocene epoch relatively unscathed. Second: if–and it is a big if–the human population remains relatively stable after the twenty-first century, or declines, and we develop increasingly efficient means of obtaining our food, then the currently increasing human demand for land may go into reverse. ‘Peak land use’ may be achieved in the next hundred or so years, with pressures progressively reducing thereafter. That should be our goal.