The God Species: How Humans Really Can Save the Planet...

But our story follows a different group of mammals who struck out in a new direction. They headed off not into the land or out to sea but up the trees. Perhaps to escape predators on the forest floor, or to take advantage of succulent arboreal fruits, the lives of these ‘prosimians’, who appear in the fossil record about 55 million years ago, demanded a whole new set of skills. The paws of their ratlike ancestors evolved into gripping hands, more suited to a life spent grasping branches. Their requirement for smell declined. But their need for vision increased enormously, and not just any vision: their eyesight had to reveal excellent colour, and, most important, had to be front-of-head and stereoscopic to give depth perception.

The pressure was on for bigger brains. Mental calculations performed whilst speeding through the treetops had to be fast and accurate. Memory was once again useful, aiding decisions as to what types of trees could support what weight, how to grasp certain branches, or when to visit different fruiting bits of the forest. These were still small animals, but as they evolved better agility in the forest, their bodies grew larger. By 35 million years ago, true monkeys had appeared. By 22 million years ago, gibbons had split away from the evolutionary line. Orang-utans followed, at about 16 million years ago, and chimpanzees 6 million years ago. That left the hominids, and we are their only surviving descendants – all other hominid species, of which there have been a dozen at least, were destined to perish.

BIRTH OF THE FIRE-APE

Our lineage may be ancient, but modern Homo sapiens has been a very short-lived phenomenon, perhaps illustrating the biological anomaly that we are. Although bipedal hominids were stalking the African plains as long as 3 million years ago, true Homo sapiens – the evolutionary descendant of Australopithecus, Homo habilis and later Homo erectus – appeared less than 500,000 years ago, and perhaps as recently as 200,000 years ago.

Mitochondrial DNA passed through the maternal line suggests in fact that we are all descended from a single individual – the so-called Mitochondrial Eve – who lived in Africa 200,000 years ago. Further evidence comes from the remarkable homogeneity of human DNA: despite superficial differences in hair straightness, noses and skin colour, we are far more closely related than might be expected. (A single breeding group of chimpanzees will show more genetic variation than do all humans.7) This is strong evidence that modern humans did all descend from the same original group, and our dominance may have begun with a characteristic act of genocide, as the last Homo neanderthalensis survivors were ethnically cleansed from Europe and Asia by the new migrants. Since then, no other animal, whether on two legs or four, has challenged the dominance of Homo sapiens.

The most striking biological characteristic of the human ancestral line over the last few million years is the extraordinary progress of its brain development. Chimpanzee brains measure about 360 cubic centimetres in volume. Early Australopithecus had expanded its brain to about 500 cm3, whilst Homo erectus measured up with a brain size of about 800 to 900 cm3. Half a million years ago, the brain was expanding at an extraordinary rate of 150 cm3 every hundred thousand years.8 Modern humans typically have a brain size of 1,350 cm3, nearly four times the size of those of our nearest relatives, the chimpanzees.

One human innovation is often neglected in accounts of our evolution – and it may be one of the most important of all, because it allowed us to fuel our process of encephalisation (increased braininess). The brain is a very energy-hungry organ, consuming a quarter of all our energy use, as compared with 10 per cent in other primates and 5 per cent in most mammals.9 So how were the extra food requirements satisfied? Part of the answer is almost certainly the increasing amounts of animal protein in the human diet – hominid species quickly supplanted leopards as the dominant hunters on the African plains. But just as important was the advent of cooking, which enables food to be transformed into much softer and more calorific forms before being eaten. For over a million years humans have been eating cooked food, giving us a dietary advantage no animal has ever enjoyed before.

Cooking, of course, needs fire. Indeed there is a strong biological case for seeing humans as a co-evolved fire species. Fire made us physically what we are, by allowing us to grow vastly bigger brains through eating cooked food. The human gut is much smaller, and uses far less energy, than the digestive system of comparable animals. We also have weak jaws, small mouths and underdeveloped teeth compared with other primates. That first acquisition of fire acted as a powerful evolutionary driver, enabling humans to become the first truly sentient beings in history.

Fire, however, is a very special tool. Not for nothing is it identified in many human cultures as the preserve of the gods. Bonfires lit at the Celtic festival of Beltane symbolise the return of the sun to warm the Earth after the freezing nights of winter. In Navajo tradition, Coyote – who was a friend of humans – tricked two monsters on ‘fire mountain’ into letting him light a bundle of sticks tied to his tail, which he then took back to people. Perhaps the best-known fire tale of all is that of Prometheus, the Titan of the ancient Greeks (and son of Gaia, goddess of the Earth), who stole fire from the supreme god Zeus and brought it back to people. For this transgression he was punished by being chained to a rock and having his liver eaten out each day by an eagle.

And rightly so, for fire dramatically changed our relationship with the natural world. Acquiring the power of gods separated humans permanently and irretrievably from all other species. As well as cooked food, it afforded protection against predators and warmth on cold nights, allowing early humans to spread north out of Africa during the depths of the last ice age. Fire may have facilitated the spread of genes for hairlessness, as the need for body insulation diminished. However, once our hair was lost and our guts had shrunk, we were tied to the hearth – we could no longer exist without it.

No human can hope to survive in the wild today without fire, and this dependence marks a major qualitative shift in human relations with the biosphere. Other animals need only food. We are the only animal that has learned to harness an external energy source in a systematic way, through our reliance on fuel. It is this food–fuel relationship that most defines the fire-ape, Homo pyrophilus. Moreover, this innovation was perhaps the most important one in unbalancing our relationship with nature, for being armed with fire put the rest of the world at our mercy.

However, our dependence on fuel could also be a weakness. Once the forests were chopped down and the landscape denuded, humans might no longer be able to flourish. The story of the modern era, however, is the story of our transcendence over even this limitation. For modern humans were to discover a new source of fuel that would allow us to expand both our numbers and our dominance dramatically. This new fuel, in the form of underground deposits of fossilised biological carbon, was to be the energy springboard that catapulted our species – and the planet – into an entirely new geological era, the Anthropocene. Using the tool of the gods, we were to become as gods. But unlike Zeus, we still live in ignorance about our true power. And time is running out, for the flames of our human inferno have begun to consume the whole world.

Chapter Two

The Biodiversity Boundary

Our fire-sticks and engines have turned humans into extremely successful predators. We have poisoned, outcompeted or simply eaten so many other species that the Earth is currently in the throes of its most severe mass extinction event for 65 million years, and it is this crisis of biodiversity loss that arguably forms humanity’s most urgent and critical environmental challenge. Many of our other impacts on the Earth system are more or less reversible, but extinction is for ever, and a flourishing diversity of life is essential for the biosphere to function successfully during the Anthropocene and beyond. By removing species, we damage ecosystems, collapse food webs and ultimately undermine the planetary life-support system on which our species depends just as much as any other.

The planetary boundaries expert group proposes a biodiversity loss boundary of a maximum of ten species lost to life per million species per year. The current rate of loss is already one or two orders of magnitude greater than this: conservationists estimate that 100 to 1000 species per million are currently wiped out annually. Meeting this boundary target is possible, but to do so will require a massive increase in the global attention and funding given to the issue and to solving it. We must create many more nature reserves, both on land and at sea. We must properly fund conservation, to defeat poachers and protect wildlife from direct threats. Above all we must alter our accounting systems so that living systems – from rainforests to polar tundra – are given the value they deserve as literally priceless assets of natural capital. This means using the power of markets, with most payments for biodiversity protection going to the local people who are always the best custodians of their local environment.

If we are to save what remains of the glorious diversity of life on Earth, we will have to act fast. A quarter of the world’s mammals, a third of amphibians, about 13 per cent of birds, a quarter of warm-water corals, and a quarter of freshwater fishes are globally threatened with extinction. The rate of loss is accelerating, despite increasing concern about this brutal devastation of our planet’s natural history: whilst 36 mammals improved in terms of how threatened they were between the 2007 and 2008 Red Lists, 150 saw a deterioration, from vulnerable to endangered, from endangered to critically endangered, or critically endangered to extinct.1

In 2002 world governments agreed a target ‘to achieve by 2010 a significant reduction of the current rate of biodiversity loss at the global, regional and national level as a contribution to poverty alleviation and to the benefit of all life on Earth’. Laudable, of course. So was it met? Not even close. To put numbers on the current crisis, a recent report in Science looked at 31 different indicators – things like habitat quality, population trends, extinction risk and so on – and found that virtually all of them were either getting worse or showed no improvement in the last decade.2 Stalin said that the death of one person was a tragedy, the death of millions a statistic (and he was an expert). So it seems for species too. Each story is a unique tragedy, yet the aggregated numbers somehow fail to convey the magnitude of this loss.

Even where absolute extinction has been avoided, many species have become functionally extinct in the sense that their remaining numbers are so few – or so scattered – that they no longer play any effective part in the ecosystem. The Iberian lynx, for example, is not extinct – not yet – in the wild, but its total population (between 84 and 143 adults; split into two isolated populations in Spain) is so tiny that it can hardly still be considered the apex predator it once was. (The lynx may be completely extinct in neighbouring Portugal: its survival has been inferred only by the discovery of a single dropping, identified by molecular analysis in 2001.3) Globally the abundance of vertebrate species fell by nearly a third between 1970 and 2006, according to the 2010 Global Biodiversity Outlook.4 Forget about extinctions: there are now a third fewer wild animals in total on the planet than there were forty years ago. That really is a shocking figure.

Even emblematic species like the tiger have their backs to the wall. Globally, only about 3,500 wild tigers remain – an extraordinary statistic given the charisma and recognition factor of this species, whose form has been emblazoned on everything from cereal packets to petrol stations. Three subspecies, the Bali, Caspian and Javan tigers, are already extinct; the South China tiger has probably joined them, for no one has seen it in the wild for 25 years.5 According to a late-2010 study, the decline in tiger numbers ‘has continued unabated’ for the last two decades: only 1,000 breeding females now survive, over less than 7 per cent of their historical range. Several Indian so-called ‘tiger reserves’ no longer have any tigers in them at all. Yet saving the tiger could cost as little as $82 million per year, according to one estimate – this is all it would take to protect the remaining 42 sites around Asia where viable tiger populations remain.6 All that is needed is a mechanism to raise the funds and an implementation plan to safeguard the reserves.

Particularly badly hit by our success have been our nearest relatives, the great apes. All are threatened with extinction in the wild. In Asia the orang-utan – once common from South China to the Himalayas – is now reduced to a remnant of between 45,000 and 69,000 individuals, mostly in the sort of lowland forests in Borneo that seem to be particularly irresistible to oil-palm plantation owners. In Africa the famous ‘gorillas in the mist’ of Virunga National Park in the Congo are down to about 380 individuals, under siege by marauding rebels as well as by poachers and bushmeat hunters. To put humans in our proper context, try entering ‘great apes’ into a www.iucnredlist.org (a website run by the International Union for the Conservation of Nature, featuring its Red List of endangered species) search. When I tried, the results were as follows:

Gorilla beringei (Eastern Gorilla) – Status: Endangered, Pop. trend: decreasing.

Gorilla gorilla (Lowland Gorilla) – Status: Critically Endangered, Pop. trend: decreasing.

Homo sapiens (Human) – Status: Least Concern, Pop. trend: increasing.

Pan paniscus (Gracile Chimpanzee) – Status: Endangered, Pop. trend: decreasing.

Pan troglodytes (Common Chimpanzee) – Status: Endangered, Pop. trend: decreasing.

Pongo abelii (Sumatran Orang-utan) – Status: Critically Endangered, Pop. trend: decreasing

Pongo pygmaeus (Bornean Orang-utan) – Status: Endangered, Pop. trend: decreasing

As this list shows, we are just apes. But with our newfound global power comes a responsibility for proper global stewardship. This is a new task for humans to take on, certainly at a planetary level. But the time for this shift is long overdue, for a brief review of our history to date shows us in a very singular role: that of serial killers.

THE PLEISTOCENE OVERKILL

Many thousands of years ago a dramatic ecological calamity began to sweep through the fauna that inhabited the Earth’s disparate continents. Australia lost most of its large animals first, about 46,000 years ago. North and South America saw a similar extinction wave 13,000 years ago. New Zealand, meanwhile, kept hold of its big-bodied animals until a mere 700 years ago. What happened at each of these points in time? Did the climate perhaps change, leaving large animals stranded? Unlikely: there is no correlation between global climate change and the various extinction pulses. Did a meteor strike or a volcano blow? Again, there is no way to pin all of these different calamities, taking place at very different times, on a single geological event. Indeed, the true nature of this extinction calamity is much more familiar. It came on two legs, for a start. What links these points in time is simple: they mark the moment when humans arrived.

Modern humans have at least dealt out death fairly: we began our existence by killing each other. In what looks like a prehistoric bout of all-too-modern ethnic cleansing, Homo sapiens probably drove its closest hominid relatives, Homo neanderthalensis and Homo erectus, to oblivion. A minority of archaeologists cling to the notion that some interbreeding must have taken place, but genetic studies show this is unlikely.7 Modern human DNA instead confirms that all of us are descended from the same small initial Homo sapiens population that migrated out of Africa 50,000 years ago.8 The last Neanderthals hung on in remote mountainous parts of France until 38,000 years ago, and in southern Spain until about 30,000 years ago. The very last families died a few thousand years later in Gorham’s Cave in what is now Gibraltar, when their final refuge on the extreme southern edge of the continent was overrun.9 Officially, the direct cause of their ultimate demise is a mystery, but I think we can guess who the culprit was.

There is certainly enough evidence to mark out a crime scene. One Neanderthal skeleton discovered in Iraq bears a peculiar puncture wound on one of its ribs – a mortal injury that is most consistent with a spear thrown by an anatomically modern Homo sapiens.10 In early 2009, the anthropologist Fernando Rozzi reported the discovery of a Neanderthal child’s jawbone, found together with anatomically modern human remains at the cave of Les Rois in southwestern France.11 The bone bore characteristic cut marks, similar to those found on butchered reindeer skulls, suggesting that the tongue had been cut out and eaten. Some loose teeth scattered around also had holes drilled in them, perhaps as parts of a morbid ceremonial necklace. Rozzi drew an unequivocal conclusion: ‘Neanderthals met a violent end at our hands, and in some cases we ate them,’ he said.12

There is even stronger evidence surrounding who killed most of the world’s largest animals, for their butchered bones are found stacked up everywhere humans invaded. As palaeontologist Richard Cowen writes in The History of Life, ‘From Russia to France, [archaeo-logical] sites contain the remains of thousands of horses and hundreds of woolly mammoths.’13 But the slaughter was far worse in the New World, where native species had no previous experience of this naked and harmless-looking but surprisingly rapacious two-legged predator. The North American death toll included six species of ground sloths, two species of mammoths, all mastodons, a giant bison, seven species of deer, moose and antelope, three species of tapirs, the North American lion, the dire wolf, the giant anteater, the giant turtle, the giant condor, all ten species of North American horses (then absent until reintroduced by invading sixteenth-century Europeans), two species of sabre-toothed cats, eight species of cattle and goats, the North American cheetah, four species of camels and two species of large bears.

But the biggest wipe-out of all took place in Australia, which saw a near-total extinction of large wild animals. The continent lost some extraordinary creatures: a gigantic horned turtle as big as a car, enormous flightless birds standing more than 2 metres tall and weighing half a tonne, a snake 6 metres long, and a giant predatory lizard that grew up to 7 metres in length and must have been the most fearsome reptilian predator since the dinosaurs. About twenty species of large marsupial disappeared, including a cow-sized wombat and a kangaroo 3 metres high. Quite how and when they died remains controversial: many archaeologists have tried to absolve Homo sapiens of the crime, pointing to the lack of kill sites and the low density of human population. But the extinction is roughly coincident with human arrival in the continent, and the pattern – affecting the largest species disproportionately – is exactly the same as everywhere else.

Further damning evidence comes from Tasmania, which retained its giant kangaroos (and various other megafauna) for four thousand more years, until falling sea levels allowed humans to finally invade – whereupon the island’s giant kangaroos (amongst six other large-bodied species) promptly died out.14 Any remaining doubters need only look to New Zealand. When Polynesian people first arrived by boat a mere 700 years ago, they found a unique island ecosystem where – thanks to millions of years of geographical isolation – birds rather than mammals or reptiles had evolved to become the dominant land animals. Giant flightless moas stalked the forests, whilst enormous eagles, the largest ever known, with wingspans of the order of 3 metres, soared above the mountains. Within as little as a century all – along with half of the islands’ other terrestrial vertebrates – were dead.15 This time there can be no dispute as to the cause of death or the identity of the killers, for Maori dwelling sites are surrounded by piles of moa bones – some so extensive that they have since been quarried for fertiliser. No doubt believing that the abundance of their moas would last for ever (another pattern that keeps repeating itself), the Maoris wastefully ate only the upper legs and threw the rest away.16

Only one continent’s large animals survived relatively unscathed. That continent was Africa, whose megafaunal inhabitants had co-evolved with hominids over millions of years and had therefore acquired a great deal of useful experience about living with Homo sapiens. As a result, Africa gives us the best idea of what a pre-human landscape might have looked like, with big animals like elephants browsing the undergrowth and herds of wild horses and cattle stirring up dust clouds across the savannah. Indeed, African ecosystems have been used as a model for proponents of ‘rewilding’ parts of North America; if cheetahs, elephants and camels can be imported into places like Montana, perhaps they could assume the ecological niches vacated by their extinct relatives, some have suggested.17 This is a romantic but vain hope, not least because the ancient homeland of these large surviving animals is seriously endangered by today’s generations of human beings. Africa is safe no more.

Right across the world, these lost big animals left ‘ghost habitats’ behind – trees that still bear specialised fruits hoping some long-gone giant will distribute them, or thorny bushes protecting themselves against browsing by extinct large herbivores. In Brazil, more than 100 tree species still produce obsolete ‘megafauna fruit’, evolved for dispersal by extinct elephant-like creatures called gomphotheres. Not surprisingly, with no living animals to disperse their seeds, these trees are now themselves becoming endangered. In Madagascar many plants grow thin zig-zag branches to protect themselves from leaf-munching elephant birds, another giant flightless bird that became a casualty of Homo sapiens – and that laid eggs so large it is thought to have inspired the legend of the roc in Sinbad the Sailor. Modern-day Siberia’s wet peaty tundra may stem from the loss of the mammoths, whose earlier grazing nourished a much more productive dry steppe-type biome before their extinction at human hands a mere 2,000 years ago.18 In Africa elephants play a key role in opening up forests by pushing over trees – a function their relatives in the Americas would also have served before being wiped out by man. In all cases, the vanished megafauna maintained a more diverse ecosystem than the simplified one that replaced them after their sudden demise.

All told, the Quaternary Megafaunal Extinction between 50,000 and 3,000 years ago carried off about a half of the world’s large animals (including 178 species of large mammals). This was an extinction wave that bears comparison with the largest in the geological record – but it is still only a prelude to what was to come. The wipe-out that accompanied human migration across the continents was restricted only to the most large-bodied and easily targeted species. In comparison, today not only are the largest animals still at risk, but also small amphibians, songbirds, flowering plants, insects and much else besides. The Sixth Mass Extinction, or the Anthropocene Mass Extinction, is already well advanced – and the death toll will soon rival that at the end of the Cretaceous, when the dinosaurs (and half of the rest of life on Earth) disappeared. Today the small as well as the large wait in line for the cull.