Inheritors of the Earth

by Chris D. Thomas

  Furthermore, it seems completely unreasonable to suggest that today’s half-million North American bison (with a genetic soupçon of auroch) can possibly be having anything like as much impact as the 30 to 60 million that used to roam North America as recently as the 1700s. An additional irony is that it has just been discovered that the European bison, the wisent, originated as a hybrid between wild auroch cattle and steppe bison (a close relative of the American bison) about 120,000 years ago.30 Intensive conservation efforts are lavished on the hybrid wisent. While conservationists will dismiss this hybridization as too long ago to worry about, measured against the long timeline of life on Earth, this ‘ancient’ hybridization happened at more or less the same time as the modern hybridization between the cattle and American bison. Yet our responses to the two events are very different.

  There seems to be a deep-seated feeling that every animal should be pure, whereas we know that, in reality, every individual of every species is likely to have at least some degree of past hybridization lurking within its genes. This attitude to genetic purity makes no biological sense, and it is not a viable way of managing the Earth. The exchange of genetic information between organisms that we usually think of as distinct–hybridization–is one of the ways in which new genetic forms come into existence and genetic fitness can potentially be increased. Hence, it is an important part of the history, present and future of life on Earth. The idea that humans can or should police hybridization is ludicrous.

  These new connections are unlike any previous period in the Earth’s history. The explosion that killed off the dinosaurs, and the other four major episodes of mass extinction in the last half-billion years, did not transport vast numbers of the survivors around the planet on a timescale of hundreds to thousands of years. There was no equivalent bringing together of species from different regions. The nearest equivalent is when continents have collided, generating periods of increased extinction and increased diversification. However, the biological joining of South and North America took place over several million years, rather than centuries, and the coming together of Pangea from previously separated continents took about 100 million years. Even when the world’s land did form a single continent, the connections were not as great as now. Pangea was the combined size of all today’s continents, so movement between distant locations would have been limited–just as many species have not (until recently) been able to move between the opposite ends of Eurasia, between the east and west coasts of North America, or between eastern and western Australia. We are even transporting species to remote oceanic islands, which would have remained isolated when Pangea existed. Given the geographic distances and rapidity of connections that are taking place in the Anthropocene, there is no precedent since multi-cellular life forms colonized the land.31 I find it difficult to imagine a period in the entire history of terrestrial life on Earth when the speed of origination of new evolutionary lineages could have been faster, as a result of the combined forces of populations arriving in new locations and starting to diverge there, the previous residents becoming adapted to the new species that arrive, and new hybrids coming into existence as species meet up for the first time in new habitats and new geographic locations.

  This brings us back to the rate at which new species are forming. More new plant species have come into hybrid existence in Britain in the last three hundred years than are listed as having died out in the whole of Europe, and the one casualty is a species of violet that is closely related to other species of European violet.32 I’m sorry to see it go, of course. The number of new plants that have formed as novel hybrid species in North America, such as the American salsifys, is also greater than the number of species of plant that are recognized as having become extinct. The beautiful creamy, camellia-like flowers of the Franklin tree, whose pendulous leaves turn a fiery red in the autumn, disappeared from the banks of the Altamaha River in the state of Georgia in the early 1800s. This appears to be the only higher plant listed by the International Union for the Conservation of Nature (IUCN) as having become extinct in the wild on the United States mainland. This is a real shame, but you can still buy its seed, obtain cuttings and order potted plants. It is not actually extinct. It has abandoned the Altamaha River in favour of its new habitat–suburban gardens and parks. The IUCN list is probably not complete33 but, on the face of it, the current rate at which new flowering plant species are forming in the landmass of North America is at least on a par with the extinction rate, as in Europe.

  Given that we lack a proper inventory of all the new species that have come into existence (just as the inventories of living and extinct species are incomplete), we should be cautious and simply conclude that plant originations and extinctions may be comparable in these two parts of the world. I do not wish to downplay the losses, particularly in regions where major new land clearances are taking place. The world has probably lost more plant species in the last three hundred years than we have gained, and more vertebrate animal species have disappeared than new ones have formed. Yet new hybrid animals as well as plants are coming into existence and populating the Earth at a faster rate than ever before.

  The human era is undoubtedly a time of unusually rapid extinction. We should regret the losses–but we should also applaud the gains. We are living through a period of the rapid formation of new populations, races and species. In the end, the Anthropocene biological revolution will almost certainly represent the sixth mass genesis of new biological diversity. It could be the fastest acceleration of evolutionary diversification in the last half-billion years. Some might discount these new species as weeds and pests, but that is a reflection of the human mind, not a fundamental attribute of these new forms of life. All forms of life simply come into existence on account of their individual histories and take advantage of the resources that are available to them. If some of these thrive at our expense, that is our problem, not theirs.

  PART IV

  Anthropocene Park

  Prelude

  It is perhaps time to take stock of the changes that are taking place, before we move into the final section of this book, which concentrates on our attitudes to the biological world and our strategies to protect it.

  Parts I and II illustrated the dynamic nature of wildlife. Nature never sits still. While some species have declined or become extinct, others have thrived, and nearly all the species that most of us see around us every day are, at least to some extent, beneficiaries of a human-altered planet. Our encounters with large animals have left many species extinct, but our domestic animals and plants are now widespread, and the largest wild species that have survived are starting to recover in many regions of the world. While it is inevitable that fewer species now live in any given square metre of fields that are used for intensive food production, the world’s biota has been remarkably resilient. We altered the world’s habitats, and vast numbers of species have taken advantage of the new conditions. We changed the atmosphere, and hence climate, and species have spread into new regions as a consequence. And we have directly transported species to new parts of the world. The upshot is that all species are now living in human-altered environments and a high proportion of all the world’s species are also living–at least somewhere–in new locations. These represent biological gains for animals, plants, fungi, microbes, viruses and any other kind of organism you wish to mention. Furthermore, the overall consequence of the arrival of new species into each region, be that a particular country or island, has been to raise the biological diversity of that part of our planet.

  These dynamic changes are not fundamentally different from those in the past, other than that humans are directly or indirectly responsible for them. Dynamic changes to the locations where species live is how they survived the ice ages. It is how species are surviving now and, if we wish to maintain the world’s biological resources, which I will argue in Part IV is a sensible human strategy when we face an unknown future, we should not try to halt biological change. I would certa
inly advocate that we tackle the underlying causes of change: we should stabilize and then reduce the human population, minimize levels of harmful consumption, obtain our food in ways that reduce our footprint on the Earth, and minimize and when possible recycle the waste we produce. We should also reduce our greenhouse gas emissions. But we should not normally attempt to halt how the biological world responds to the consequences of humanity, except when those responses are directly and obviously injurious (we will, of course, want to control new human diseases, crop pests and pathogens that afflict our livestock). Biological change is how life on Earth survives. Treating each arrival of a species in a new habitat or geographic location as something to be resisted will, in most instances, result in failure, and it is ultimately counterproductive. Humans must adapt to and help direct change, rather than attempt to preserve the world in aspic.

  Over longer durations, the entire history of life is a narrative of change, involving both changes to the distributions of different types of organisms, and evolutionary changes to the sorts of creatures that live on Earth, as I discussed in Part III. Life is the product of evolution, and evolution is how life meets each new challenge. When the world is altered, as it has been by the rise of humans, it is met by evolutionary change. Some species do not make it, but others continue to live, and go on to perform roles in the next act of the world’s evolutionary play. This evolutionary changing of the guard involves certain types of species surviving while others (such as flightless island birds) disappear. It also involves evolution within every population of every species, evolution when species arrive in new locations, and hybridization when dissimilar but related forms meet. These processes of biological renewal have accelerated to unprecedented levels as humans have transformed habitats and transported species around the world. A massive evolutionary genesis has been taking place over the last ten thousand or more years, and the rate of evolutionary change continues to accelerate. Life on Earth survives because it changes.

  The inevitability of ecological and evolutionary change in the human epoch brings us back to our starting point. The fundamental process of life is simply the passage of information, chemically coded in our DNA, and this information is used to build the bodies of each successive generation. The consequence of the error-strewn transfer of information through time has been an immense diversification of life on Earth, in which there are both gains (new types come into existence) and losses (some types disappear). This dispassionate process means that the only value judgements we can make about these gains and losses are our own, as individual humans and as a society. As such, we need to contemplate carefully the relationship between humanity and nature. This is the subject of Chapter 10, in which I argue we should genuinely accept that we are ‘as one’ with nature. We are part of nature. Once we have sorted this out, it is possible to take a considerably more positive attitude to natural changes and to conservation–the topic of Chapter 11. We can think of the world as a biological park, Anthropocene Park, with ourselves both as custodians and inmates. For better or for ill, this is the world we inhabit.

  10

  The New Natural

  Oscar Wilde prided himself on being as unconventional as possible, but when he dismissed nature as ‘a place where birds fly around uncooked’ and explained that ‘if nature had been comfortable, mankind would never have invented architecture’, he was simply expressing the prevailing opinion of the nineteenth century. He enjoyed taunting urbanites who retreated to the countryside at the weekend; nonetheless, they shared his views about the separation of nature and humanity. The only difference was that Wilde wanted to escape from nature, while they wanted to escape to it. Looking past his witticisms, Wilde was, on this occasion, giving voice to a societal norm. The distinction between nature and humanity was a God-given separation for the majority of the population who believed in a deity, and it was still widely accepted by those who did not.

  The separation myth persists to the present day,1 despite the fact that Darwin and Wallace published their theory of evolution while Wilde was still a child, over 150 years ago.2 For example, the English language requires me to refer to ‘who’ when referring to a human, but ‘which’ or ‘that’ when speaking about animals and plants, as though they were stones. Adventure programmes and wildlife documentaries frequently serve up a diet of an idealized and separated nature.3 Nature conservation is commonly represented as an activity whereby humans do ‘good things’ for nature, while others take a more utilitarian view, in which nature is something ‘out there’ that benefits humans. And scientists usually treat human impacts as external drivers of change rather than as integral parts of the system. The separation myth permeates scientific and journalistic writing to such an extent that our planet’s natural history is even said to have become its unnatural history.4 Yet we know, objectively, that the human species evolved naturally, so humans must be natural. We are part of nature. Accepting this, the perspective that ‘humans are making nature less natural’ is equivalent to saying that ‘nature is making nature less natural’. This does not make sense.

  Consider the past. The catastrophe that befell T. rex and the other huge dinosaurs was unusual in that it originated in space, whereas most other mass extinctions in the history of the Earth appear to have been caused by natural internal changes within the Earth system itself–some geological and some biological. Outpourings of lava, climate-altering changes to the position of the continents and depletion of oxygen in the oceans have caused mass extinctions whenever these cataclysmic geological events5 created conditions that were beyond the tolerances of the majority of species then alive. Other extinction events have arisen when entirely new types of living thing have evolved. The evolution over 2 billion years ago of photosynthetic Cyanobacteria that could trap energy from the sun ultimately generated so much free oxygen–a waste product of the new chemical reaction–that they made the atmosphere and oceans toxic to most of the Earth’s previous inhabitants. That biological event opened up new evolutionary opportunities for multicellular life forms that could develop an oxygen-based metabolism. Crickets, crabs, cuttlefish, cod, caiman, crows and cheetahs would not be possible but for that oxygen.

  Today, a rapid increase in the rate of extinction is again being driven by an unprecedented evolutionary event arising within the Earth system: the rise of an unusually brainy and linguistically capable primate. Some 7 million years ago, our predecessors were African primates.6 They were intelligent, sociable apes who lived predominantly on the ground but climbed trees for food and used a small number of basic tools. If we saw a living specimen of this animal, we would be unanimous that it was not human and that it was part of the natural world. But it continued to evolve. We can surmise that two or more populations of this ape separated, living in geographic regions within Africa where the climate, vegetation and availability of food differed. These populations would have diverged, such that the apes from each region would no longer possess exactly the same behaviours and physical attributes, in the same way that humans from different parts of the world can today be recognized. Given enough time, these separate populations eventually split into two or more related species, although they continued to hybridize every so often. But still we would agree that they were not human and that they were part of the natural biological system.

  Many new apes emerged along the way, of which just two branches survive today, one becoming ground-living humans, the other forest-adapted chimpanzees and bonobos (our shared ancestry with the other great apes goes back to an even earlier time), which evolved elongated fingers and an increased ability to swing through the trees.7 Our own line came out of the trees, ran on its back legs, lost body hair, lived in complex social groups, enlarged its brain, developed more sophisticated tools, controlled fire and acquired complex communication. These evolutionary and cultural developments in turn led to the runaway social innovations of the last few thousand years, including our ability to use intricate languages, domesticate animals and plants and b
uild cities, as well as our capacity to develop religions, dictatorships, monarchies, democracies, bureaucracies, trade networks and other systems of co-operation and control on increasingly large scales.

  When we contemplate the biology and impacts of humans on the Earth, there is no doubting that Homo sapiens is an extremely unusual animal. But at what point in the unbroken sequence of generations should we decide that humans ceased to be part of nature, and at what point did the effects of humans on the rest of the world become unnatural? There is no scientific or philosophical justification that could be used to separate this continuum of ape-then-human animals into two qualitatively separate categories. Evolution took place for long enough that we are recognizably human, and chimps are recognizably chimps. In many ways, we are still very similar, however–we shared the same great-great (add something like 250,000 more ‘great’s) grandparents. Chimps can also go grey and show receding hairlines as they age, they live in complex social groups, sometimes run on their back legs, have extremely large brains and use tools. They can communicate sufficiently to pass on cultural information, undertake group hunts and organize the equivalent of warfare between chimp communities.