Inheritors of the Earth

Prologue

Gains and losses

The Vale of York is a landscape of ecological despair. Billowing clouds emerge as condensation from the cooling towers of distant power stations and then rise above the plain. Fields of wheat, barley and oilseed rape disappear towards its flat horizons. Ploughs and combine-harvesters trundle where brown bears once snuffled through primeval forests and wild cattle wallowed in peaty swamps. It is one of the most intensively farmed parts of England, and England is one of the most densely populated countries in Europe.

Yet when I survey this landscape from my study window, I see a green world punctuated by scarlet specks of poppy flowers swaying in the breeze. Coppery pheasants are strutting in search of fallen seeds, dowdy field voles are scurrying back and forth below tussocks of grass, and camouflaged greenfly are jostling for position as they suck juices from the veins of young leaves. Their enemies are on the prowl too. Rufous foxes are sniffing out a pheasant meal, hovering kestrels are watchful for the slightest movement of a vole, and dangerous harlequin ladybird beetles are laying waste to the greenfly. Lines of helmet-sized molehills hint at the life below ground, where microbes and fungi decompose fallen leaves and velvety moles consume gritty worms. A water vole is burrowing through a mat of pigmyweed in the pond.

The apparently denuded vale is full of species, and many are world travellers. The harlequin ladybirds originated in Asia; the small-leaved pigmyweed in Tasmania; poppies came as contaminants of grain from continental Europe; and kestrels arrived under their own volition, able to catch their rodent prey once the forest was cleared. In contrast, the tunnelling moles have survived generations of tumult as the ancient forest was converted into farmland; now they burrow beneath road verges and grassy lawns. Although these players and the scenery of life's game–the species and habitats–have changed on account of the presence of humans, the basics of biology remain. Regardless of their origins, the plants growing in the fields, roadsides, ditches, hedgerows, gardens and scattered copses still capture energy from the sun and convert it into leaves, rendering the world green; animals consume plants and their seeds and in turn are killed and eaten by other animals. Decomposing plants, animals and faeces are recycled as nutrients, used by next year's growth. The rules of life continue, save Homo sapiens is now a key player.

It is the same elsewhere. Familiar creatures have taken the human-modified Earth by storm, be they talkative yellow-billed Indian myna birds that are now at home in Florida, Japan, Sumatra, Madagascar and Australia, agile mice that started life in Asia and then spread throughout the cities, towns and farmsteads of the world, or Australian wattle trees and previously endangered Californian pines that are growing wild in Africa. They are joined by thousands of other mammals, birds and plants, as well as by microbes, fungi, worms, snails, shrimps, insects, fish, toads and lizards. The trickle of successful species¹ taking advantage of human-created opportunities is becoming a torrent. Seemingly, there are as many winners as losers.

We should certainly mourn the losses. The biological and physical processes of the Earth already bear the indelible signature of humanity–this is why scientists are increasingly referring to the present day as the Anthropocene epoch. We have converted a third of the world's vegetation to produce our food, leaving a diminishing space for wild plants and animals. We have altered the great chemical cycles of the Earth beyond their historical bounds, acidified the oceans and changed the climate of the entire planet, threatening any species that cannot adjust. Our ancestors hunted most of the largest land animals to extinction, and we exterminated others by transporting voracious predators and virulent diseases to remote islands. Of those that survive, 13 per cent of bird species, 26 per cent of mammals, 31 per cent of cacti, 33 per cent of reef-forming corals and 42 per cent of amphibians are threatened in some way.² A mass extinction is in full swing, and prognoses for the future seem dire. For these reasons, we have gone so far as to describe ourselves as the scourge of the Earth, and as exceeding our planetary boundaries.

On the other hand, we are still surrounded by large numbers of species, many of which appear to be benefitting from our presence. If some species are declining but others are thriving in this human-altered world, is the prognosis really as bad as the doom-laden message of biological decline? It is important to recognize the ways our actions threaten the Earth, of course, and I will highlight many losses that have already taken place and continue to this day. However, in many respects, nature is coping surprisingly well in the human era. We should not ignore the gain side of the great biological equation of life.

It is vital that we take a broad view, considering all the evidence, if we are to draw conclusions that run somewhat counter to the 'paradigm of biological decline' that predominates among ecologists, environmentalists and conservationists. So, in this book, we will embark on a round-the-world tour of the planet's diverse continents and far-flung islands, visiting locations where my research has taken me over the past several decades. (I refer to changes in the oceans only in passing, in the interests of keeping this volume to a manageable length and because it is not my area of expertise.)³ Our journey will take in tick- and leech-filled tropical forests, bone-cold high mountains, oceanic archipelagos overrun by foreign species and landscapes devoted to the production of our food; each with its own separate human history. I also draw on insights from a wider scientific literature, based on research that has been carried out in a broader range of locations across the Earth. This is important because we live in a globalized world: our greenhouse-gas emissions warm the climate everywhere; we consume food and use timber that may have been grown on the opposite side of our planet; and species are being transported in our wake. We need a truly global perspective to understand the ramifications of our own actions.

We also need to set today's changes in their appropriate historical context, which involves time spans much longer than we are used to thinking about in our everyday lives. This is necessary because the story of life on Earth is one of never-ending change: be that the arrival and disappearance of species from a particular location (ecological change) or the longer-term formation of new species and extinction of others (evolutionary change). So we examine the responses of species and ecosystems to human impacts over periods that range from years to millennia. We will also reflect on the fates of animals and plants as they experienced ice ages on schedules of tens to hundreds of thousands of years. And we will examine the consequences when different types of animals and plants meet up for the first time, as happened several million years ago, when a land connection was made between North and South America, introducing sabre-toothed cats, four-tusked elephants, camels and tapirs from the north to a southern continent inhabited by marsupial lions, porcupines, giant ground sloths and enormous armadillos. The message is clear. Some species don't make it. Yet, it is equally clear that there are always survivors, and they persist and then thrive by moving across the surface of the Earth to places that are hospitable to them, and by evolving new capabilities. They are still doing so today.

In this journey through time and space, we make some surprising discoveries. Visits to coastal Brazil, to the tropical forests of Mexico and Cameroon and to the thoroughly transformed British Isles reveal that new species have colonized landscapes that contain a mixture of arable fields, pastures, hedgerows, plantations, orchards, logged forests, ditches and towns faster than the rate at which species that used to live in the original habitats have disappeared (as long as there are still sufficient remnants of the earlier vegetation to act as refuges for the more sensitive species). The result of these comings and goings has been that diversity has grown in nearly all regions of the world that cover areas as large as, say, Belgium or the state of Vermont. Moreover, our reliance on agriculture means that we no longer need to hunt for food as our ancestors did–hence, the numbers of bison and other large mammals are starting to rise again in North America and Europe, where the cultural transition from killing to saving animals has developed most strongly. Climate change is playing its part too. More species like it hot than cold, and so the overall consequence of a warmer climate is to raise biological diversity in many parts of the world.

This rise in the number of species in each region has been fuelled unwittingly by human action–as we have colonized all six continents, we have carried different species with us, from horses to hippos, pigeons to pythons, lobsters to lionfish. We are acting as a global glue, bringing together previously isolated biological worlds into one 'virtual continent', a New Pangea. In so doing, we are initiating a modern retelling of what has always been key to the story of life on Earth–the successful succeed. This is seen most keenly on remote islands, where introduced rats, cats, dogs, stoats and human apes have ousted tame, flightless and disease-prone birds and walking bats that have been isolated for millions of years. The continental carnivores and diseases have won, as we will discover in New Zealand and elsewhere. However, most new species that arrive do not displace any others, the consequence of which is that these islands now contain far more species than they used to. The same is true of our continents–the diversity of forest trees and shrubs is increasing in the Alps of southern Europe, for example, because many more immigrant species have established new populations than native species have disappeared. This is the norm–immigration usually increases the diversity of the recipient region.

In the longer run, the generation of biological diversity is down to evolution. The biological riches we see around us today exist because more different types of microbes, plants and animals have evolved than have become extinct over the course of the Earth's history. The Earth formed 4.5 billion years ago, single cells came into existence over 3.5 billion years ago, creatures consisting of complex bodies took off in the last 600 million years, and the diversification of life on land has occupied the last 450 million years. On average, biological gains have tended to have the upper hand, and this increasing variety of life seems likely to continue for hundreds of millions of years to come. Yes, periods when the levels of extinction are high–as they are now–represent major setbacks, but in the end they have provided new opportunities for enterprising creatures that have been able to exploit the new conditions. Nature has come back from mass extinctions before and the variety of life has grown again. Could this happen once more? Living through an age of extinction provides us with a unique opportunity to explore whether there is an evolutionary yang to the yin of human impacts.

It seems that there is–a global-scale spate of rapid evolution is in full flow. We will meet butterflies in the USA and in the meadows of Britain and Europe, and Australian crickets now living in the Hawaiian Islands, which are all evolving new ways of surviving in the human-altered world. Just as some species are thriving in modern times, some genetically distinct individuals and genes are becoming increasingly successful. Even more remarkable, new animal and plant species are coming into existence, an evolutionary signature of the Anthropocene epoch. In fact, the formation of new hybrid plant species in Europe and North America would appear to be faster already than the rate at which previously existing plants are becoming extinct. Furthermore, animals and plants which we have transported around the world are acquiring characteristics that make them less and less like their ancestors. Eventually, they will become separate species. The Earth is poised for a massive acceleration in the formation of new species–come back in a million years and we might be looking at several million additional species whose existence can be attributed to the activities of humans.

This broad geographical, historical, ecological and evolutionary context reminds us that the biological world is in constant flux. Dynamic change means that we face an indefinite future of biological gains as well as losses–often with humans the underlying cause. What are we to make of this human-altered world? The default stance of conservation is to keep things as unchanged as possible or, alternatively, to return conditions to what they used to be, or somehow to make the Earth 'more natural' (which can usually be interpreted as meaning 'with reduced human impact'). Not only are these untenable aspirations while the world's human population continues to grow and each of us consumes more resources, but hold-the-line strategies implicitly dismiss as undesirable the continuing biological gains of the human epoch. Where is the logic in this? Attempting to prevent the establishment of 'alien' arrivals and to kill 'impure' new hybrids so as to maintain our ecosystems and species in some idealized state is not possible, nor is it obvious that the past state of the world is objectively preferable to the new state that is coming into existence.

We need a new rationale for the relationship between humanity and the natural world in which humans are regarded as part of nature, given that we, too, have evolved and everywhere on Earth has already been altered by us. We have to work with natural biological processes, not against them. There is no point in taking on a never-ending fight with the inevitability of eventual failure. The new philosophy opens the door to a more optimistic approach. It permits us to be appreciative of the biological beneficiaries of the human-altered environment, while remaining cognisant of the many human-caused losses. Keeping as many species as possible alive on our global Ark should still be a primary target for our conservation activities, however, because these species and those that evolve from them are the building blocks from which every future ecological system will be constructed. They will fuel future dynamism.

Rather than swim against the tide of ecological and evolutionary change, we should remember that the old was once new. The story of life is one of diversification and renewal–successful genes and species win the game. It is time for the ecological, conservation and environmental movement–of which I am a life-long member–to throw off the shackles of a pessimism-laden, loss-only view of the world. Why should we not aspire to a world where it is as legitimate to facilitate new gains as it is to avoid losses? But before we get to this, we need to consider the success stories that have already unfolded, and how it is that humans might eventually increase the biological diversity of the Earth.