The pox that scars Eden

Cheetahs, those "icons of the open African plains" (in the words of Niles Eldredge), now crouch at the water's edge in the Okavango delta. While everyone knows of the lost garden of Eden, few have heard of the Okavango in northern Botswana. There, lushly flowing waters from the rivers Okavango, Zambezi and Chobe with their seasonal floods moisten the submerging lands between the faults that frame this masterpiece of nature. Once an ancient lake, the delta is now a vast oasis where sweet fresh water flows mutely into the soil rather than into the sea.

The Okavango delta is, in Eldredge's words, "utterly unique". Choice real estate for humans, whether for Homo sapiens or for our ancestors (probably Homo erectus), the delta has been fruitfully inhabited for at least 300,000 years. Deep spongy water, drinking grounds for the free-ranging and unfettered riot of mammals and birds, mark the rainy season. Pel's owl plunges, feet first, as it grabs bottom-dwelling fish. The Chobe bush buck hides in the high water-soaked grass. Another antelope, the sitatunga, splays its marvellously adapted toes so it can travel on marsh muck. Reed bucks haunt the exuberant odiferous wetland. In the taller grasses near the open waters, the jacana bird trots on top of water-lily leaves. Papyrus in dense stands and mopane, a tough-leaved protein-rich tree, are the key to the plethora of antelopes. These two productive members at the base of the ecosystem, along with some 80 other species of common trees (and all the other photosynthesisers - bacteria, algae and plants), supply the infrastructure of this watery wonderland.

The cheetahs appeared quite recently, in families with cubs: and their presence is bad news. For they signal the onset of drought, as they take advantage of new opportunities in the expanding grasslands of the delta. To Eldredge, the cheetah in the Okavango is a kind of miner's canary - the bird that supplied the title of one of his earlier books that explored the past history and present status of extinctions. In the case of the Okavango delta, the air is not fraught with dangerous methane, as in a coal mine - rather it is drying out.

The cheetahs are thus early-warning signs of environmental change, indicating impending "climate-induced transformations of ecosystems themselves". Ecosystem change - the replacement of one climatic regime by another - begins unobtrusively, with the conversion of forest to farmer's field.

But Eldredge describes how, in the everyday business of living on Earth, change is inevitable, easily documented and unstoppable. So, if air and soil desiccation and many other changes of ecosystem proportions are natural, why, Eldredge asks himself, "decry human-induced transformation of the surface of Earth?" His answer is simple. "By transforming grasslands and forests into farmlands, cities, suburbs and shopping mall complexes, we humans are not simply displacing ecosystems elsewhere, but rather actively destroying them, shrinking the habitat necessary to support a vast range of species. Although ecological change is natural, change too rapid or absolute leads to extinction", especially desiccation, the ultimate grim reaper against which no mere mortals can indefinitely survive.

Who cares? Why should New Yorkers whose unending sweet Adirondack water seems virtually assured worry if cheetahs appear on an obscure delta in Africa? Who cares, besides cattle owners who covet the great delta for their fertile herds, or eco-tourist leaders who envisage lucrative speedboat rides, helicopter fly-overs and Landrover approaches to the "big hairies" (elephants, buffalo and myriads of antelope)?

Not only was this gorgeous landscape our ancestral virtual Eden, says Eldredge, but it, and other natural places, are directly and indirectly connected today, as in the past, to our health. We must learn not to ignore the connections. Ignorance of our living heritage is a slow poison more deadly than food poisoning and more insidious than Lyme disease or syphilis. The cure is not better sterile processing in the food canning procedure or knowing not to leave mayonnaise out in the sun at the picnic table or a few quick doses of antibiotic. The cure for steady environmental degradation such as that of the Okavango, if there is a cure, can only be our own knowledge and wisdom.

His final section is entitled "What can we do?". Stepping back a bit from his passionate defence of nature, Eldredge offers six points for action. They may not impede the growth of urbanisation and ecosystem loss but at least they are headed in the right direction, towards some new Eden that contains the Okavango delta. They include: acknowledging the problem and stopping what remains of our local ecosystems from being transformed into the diseased tissue of the worldwide urban megalopolis; stabilising the human population; rewriting economics texts and abandoning the widely touted notion of sustainability in favour of the idea that "it's enough"; and utilising our expertise in conservation. In short, Eldredge makes a strong case that, as a worldwide culture of educated people, we must "strike a balance".

My own suggestion for action is easier and more explicit. Try to visit the new biodiversity exhibit at New York's American Museum of Natural History (opens May 30), where Eldredge has been chief scientist for a number of years. This book forms the intellectual backdrop to that 11,000 square-foot exhibit. Life in the Balance is written for the general public, especially the museum-going public. The text is engaging and hugely informative, and is supplemented by useful appendices that list, for instance, extinct species and the alternative names of 40,000 species of organisms of direct importance to people today. By the end Eldredge has inadvertently illustrated and documented a dour dictum of Nietzsche, from the 18th century. "The earth is a beautiful place, but it has a pox called man."

Lynn Margulis is professor in the department of geosciences, University of Massachusetts, Amherst, United States.