Let's finally consider two arguments that accept the reality of the extinction crisis but dismiss its significance. Firstly, is extinction not a natural process anyway? If so, why make a big deal about the wave of extinction happening now?

The answer to this first argument is that the current extinction rate caused by humans is far higher than the natural rate. If the estimate that half the world's total of thirty million species will become extinct in the next century is correct, then species are now becoming extinct at a rate of about 150,000 per year, or seventeen per hour. The world's 9,000 bird species are becoming extinct at a rate of at least two per year, but bird species under natural conditions were disappearing at a rate of less than one per century, so the present rate is at least 200 times the normal rate. Dismissing the extinction crisis on the grounds that extinction is natural would be just like dismissing genocide on the grounds that death is the natural fate of all humans.

The second argument is a simple one: so what? We care about our children, not about beetles and snail darters; who cares if ten million beetle species become extinct? The answer to this argument is equally simple. Like all species, we depend on other species for our existence, in many ways. Some of the most obvious ways are that other species produce the oxygen we breathe, absorb the carbon dioxide we exhale, decompose our sewage, provide our food, maintain the fertility of our soil, and provide our wood and paper.

Then could we not preserve only those particular species that we need, and let other species become extinct? Of course not, because the species we need also depend on other species. Just as Panama's antbirds could not have anticipated their need for jaguars, the ecological chain of dominoes is much too complex for us to have figured out which dominoes we can dispense with. For instance, could anyone please answer these three questions. Which ten tree species produce most of the world's paper pulp? For each of those ten tree species, which are the ten bird species that eat most of its insect pests, the ten insect species that pollinate most of its flowers, and the ten animal species that spread most of its seeds? Which other species do these ten birds, insects, and animals depend on? You would have to be able to answer those three impossible questions if you were the president of a timber company trying to figure out which species you could afford to allow to become extinct.

If you are trying to evaluate some proposed development project that would bring in a million dollars but might exterminate a few species, it is still tempting to prefer the certain profit over the uncertain risk. Then consider the following analogy. Suppose someone offers you a million dollars in return for the privilege of painlessly cutting out two ounces of your valuable flesh. You figure that two ounces is only one-thousandth of your body weight, so you will still have nine hundred and ninety-nine thousandths of your body left, which is plenty. That is fine if the two ounces come from your spare body fat and if they will be removed by a skilled surgeon. But what if the surgeon just hacks two ounces from any conveniently accessible part of your body, or does not know which parts are essential? You might then find that the two ounces came from your urethra. If you plan to sell off most of your body, as we now plan to sell off most of our planet's natural habitats, you are certain eventually to lose your urethra.

To conclude, let's place matters in perspective by comparing the two clouds which, as I mentioned at the outset, are hanging over our future. A nuclear holocaust is certain to prove disastrous, but it is not happening now, and it may or may not happen in the future. An environmental holocaust is equally certain to prove disastrous, but it differs in that it is already well underway. It started tens of thousands of years ago, is now causing more damage than ever before, is in fact accelerating, and will climax within about a century if unchecked. The only uncertainties are whether the resulting disaster would strike our children or our grandchildren, and whether we choose to adopt now the many obvious countermeasures.

EPILOGUE

Let's now draw together the themes of this book, by tracing our rise over the last three million years, as well as our incipient reversal of all our progress more recently.

The first indications that our ancestors were in any respect unusual among animals were our extremely crude stone tools that began to appear in Africa by around two-and-a-half million years ago. The quantities of tools suggest that they were beginning to play a regular, significant role in our livelihood. Among our closest relatives, in contrast, the pygmy chimpanzee and gorilla do not use tools, while the common chimpanzee occasionally makes some rudimentary ones but hardly depends on them for its existence.

Nevertheless, those crude tools of ours did not trigger any quantum jump in our success as a species. For another million-and-a-half years, we remained confined to Africa. Around a million years ago we did manage to spread to warm areas of Europe and Asia, thereby becoming the most widespread of the three chimpanzee speries but still much less widespread than lions. Our tools progressed only at an infinitely slow rate, from extremely crude to very crude. By a hundred thousand years ago, at least the human populations of Europe and western Asia, the Neanderthals, were regularly using fire, but in other respects we continued to rate as just another species of big mammal. We had developed not a trace of art, agriculture, or high technology. It is unknown whether we had developed language, drug addiction, or our strange modern sexual habits and life-cycle, but Neanderthals rarely lived beyond the age of forty and hence may not yet have evolved female menopause.

Clear evidence of a Great Leap Forward in our behaviour appears suddenly in Europe around 40,000 years ago, coincident with the arrival of anatomically modern Homo sapiens from Africa via the Near East. At that point, we began displaying art, technology based on specialized tools, cultural differences from place to place, and cultural innovation with time. This leap in behaviour had undoubtedly been developing outside Europe, but the development must have been rapid, since the anatomically modern Homo sapiens populations living in southern Africa 100,000 years ago were still just glorified chimpanzees, judging by the debris in their cave sites. Whatever caused the leap, it must have involved only a tiny fraction of our genes, because we still differ from chimps in only 1.6 % of our genes, and most of that difference had already developed long before our leap in behaviour. The best guess I can make is that the leap was triggered by the perfection of our modern capacity for language. Although we usually think of the Cro-Magnons as the first bearers of our noblest traits, they also bore the two traits that lie at the root of our current problems: our propensities to murder each other en masse and to destroy our environment. Even before Cro-Magnon times, fossil human skulls punctured by sharp objects and cracked to extract the brains bear witness to murder and cannibalism. The suddenness with which Neanderthals disappeared after Cro-Magnons arrived provides a hint that genocide had now become efficient. Our efficiency at destroying our own resource base is suggested by the extinction of almost all large Australian animals following our colonization of Australia 50,000 years ago, and of some large Eurasian and African mammals as our hunting technology improved. If the seeds of self-destruction have been so closely linked with the rise of advanced civilizations in other solar systems as well, it becomes easy to understand why we have not been visited by any flying saucers.