The Diversity of Life 
by Edward O. Wilson.
Allen Lane, 424 pp., £22.50, February 1993, 0 7139 9094 5
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I have a friend, a fellow biologist, who lives in California. He once wrote (only half-jokingly) to the Sierra Club suggesting that to reach their conservationist goal they should change their rules. The first statute ought to oblige all members of the club never to go into the wilderness again, and to devote their time to persuading as many other people as possible to stay at home. By so doing they would preserve nature more effectively than could any conceivable Green initiative.

My own contribution to saving the world is to turn off television programmes about burning rainforests as soon as they begin. Twenty years of lamenting the coming ecological disaster has led many to do the same. There is a Leninist feeling that the easiest way out of the environmental crisis is to strangle the last panda with the guts of the last blue whale. Public patience with the fate of the planet is suffering from over-kill in much the same way as the passenger pigeon once darkened the skies of the American West, and now does a similar thing to the conservationist conscience.

Edward Wilson reminds the jaded viewer that there really is a crisis, and that – just as in 1917 – it is already almost too late to do anything about it. He gives a penetrating historical analysis of what went wrong and even has a New Economic Plan which might, just, pull us back from the brink.

A lot of ecological writing reads as if it were translated from French. Like the jungle itself, it is gloomy, impenetrable and portentous. Wilson’s book begins in the worst traditions of the Rainforest School. However, it soon gets very much better. In places, indeed, it moves along so briskly that it reads more like a biological text than a work of popularisation. Its theme is ecological diversity: why there are so many species of animal and plant, how they arise, and how and why they become extinct.

Biologists are given to self-congratulation – and have a lot to congratulate themselves about. After all, they already know all the interesting things about genetics, and soon may even understand something about evolution and animal behaviour. There is, however, a secret about modern biology: its fundamental obligation – to describe the living world – has been almost forgotten. Physics knows the exact weight of the electron and the number of stars in the Milky Way. The best guess that biologists can make is that there exist something between ten million and a hundred million living species, only about one and a half million of which have been discovered.

Most will never be found: they will be extinct before anyone gets round to discovering them; and in fact, almost no one is bothering to look, though those who do are seeing astonishing things. In one day in a small patch of Brazilian rainforest it is possible to encounter as many different species of butterfly as exist in the whole of Europe. Such forests cover only 6 per cent of the Earth’s surface, but contain at least half of all species of plant and animal. There is now a small industry which poisons the treetops to see what falls out. So many of the creatures which plummet to the ground have never been seen before that Wilson estimates there may be as many as thirty million new species of insect hiding up there. The rainforest canopy was a lost continent waiting to be discovered, just fifty feet above the heads of a generation of tropical ecologists.

Why are there so many kinds of plant and animal – and why are most of them found in the tropics? Darwin called the nature of species, and how one arises from another, the ‘mystery of mysteries’. Had he published his best-known book under its existing title today he would have been in trouble with the Trades Description Act because if there is one thing which The Origin of Species is not about, it is the origin of species. Darwin knew nothing about genetics. Now we know a great deal, and although the way in which species begin is still a mystery, it is one with the details filled in.

Wilson’s view on species is refreshingly conventional. Instead of appealing to mysterious forces which cause one kind of creature to change, at one bound, into another, he depends mainly on the Darwinian model. Animals and plants adapt to the problems with which they are faced. In time, they change genetically and, in different places, each population takes its separate way. If the process goes on long enough a new form of life – a new species – is born.

This model of speciation is simple, and is – probably – often right. However, for most of the time it depends (as does so much of evolutionary biology) on historical speculation which can never be disproved. Consider one of the most bizarre of all groups of species. There are (or were, twenty years ago) more than three hundred species of cichlid fish in Lake Victoria. Their life-styles are as different as those of the cow, the tiger and the rat. Each lives in a single lake. The conventional view is that Lake Victoria must once have dried up into many small lakes to allow each species to evolve. Apart from the fish themselves, there is no evidence that this ever happened.

Wilson has a catholic view of evolution: most of the theories of the origin of species (or of their extinction), however eccentric, get a kind word. An old biological joke (at least I think it is old) has it that the patron saint of ecology is St Patrick. If new species can arise from a predecessor without the need for a geographical barrier (sympatrically, to use the technical term and to explain the joke, feeble as it is), then it is much easier to understand why there can be hundreds of related species in the same lake or jungle. No longer does the biologist have to invent vanished mountain-ranges or disappearing lakes. The possibility of sympatric speciation has plagued the discussion of evolution since it began.

St Patrick has another part to play in ecology. Wilson himself came up with the theory of ‘insular biogeography’, an idea which is increasingly important in understanding patterns of diversity in the living world. It explains, among other things, why there are no snakes in Ireland. Instead of calling on a divine eviction of Irish serpents, biology has a more mundane explanation. Ireland is an island, and it is small. The Irish Sea is just too wide for the adder to get across, although there are plenty of places on the other side where it might thrive. There are also plenty of tiny islands very close to the English coast which are snake-free. St Michael’s Mount, a mile from the cliffs of Cornwall, has none. They may have been there in the past, but the island was not big enough to sustain snakes for long.

This balance between immigration and extinction explains why islands have odd faunas. Many species never make it – they have not had time, or the island is too remote. Those who do are at constant risk of going bust. Insular biogeography also helps to understand why tropical forests are so diverse. The rainforest is big, it is old and it is complicated. All these qualities are now at risk, and all will be impossible to replicate once the forest has gone. Small nature reserves are useless. They will be islands of forest in a sea of grass and – just like St Michael’s Mount – will lose many of the species which made forests what they were.

The new-found land of the tropics is, Wilson fears, about to disappear for ever. There are other unknown Edens as well. A handful of soil from a Norwegian forest contains five thousand species of bacteria, most new to science. At the other end of the size range, 11 new species of whale have been discovered in the 20th century. The bacteria are probably safe, but simple carelessness means that we may have lost whales we have never seen.

Most species, of course, already are extinct. Perhaps 99 per cent of all the different kinds of creature which have appeared since the beginning of life have departed, many just after they began. Fifty years ago, though, there were probably more sorts of animal and plant around than there ever had been before.

Now and again an arbitrary catastrophe snuffed some of them out. Krakatoa was a hiccup; just a century later, more than half the species vaporised by the explosion are back on what remains of the volcano. Sixty million years ago there was a much bigger bang, perhaps caused by a meteorite. The dinosaurs went (although most other groups survived). It was the fifth in a series of extinctions over half a billion years. Now we are in the sixth – a different and slower kind of bang, but one which may echo through the future for even longer than did earlier disasters.

We all know that the forests are going – but how fast! The answer is (probably) even more rapidly than the average TV viewer thinks: a football-field’s worth every second, which is equivalent to the destruction of three species an hour. There are other disasters too. Nearly all the cichlids have gone from Lake Victoria: eaten by the Nile perch, which was introduced as a food fish in the Sixties.

Many of the departed might have been useful. A wild relative of maize was discovered in Mexico in the Seventies. Unlike the cultivated form, it contains genes which makes it a perennial – the plants survive for several years, instead of having to be planted anew each spring. If these genes were introduced into crops, farming might save billions of dollars. The Jalisco maize was reduced to 25 acres of hillside when it was found; and was only a week away from being burnt out.

The forests hold other surprises. After all, just three plants – wheat, maize and rice – provide more than half the world’s food, although there are thirty thousand species which are edible. There is a wild tomato which could be irrigated by sea-water and, in the Amazon flood-plain, turtles could produce four hundred times as much protein per acre as do cattle.

Although the chances of Ronald McDonald promoting turtle soup rather than Big Macs seem remote, there is plenty which might be done to save what remains. First, there must be a catalogue of what is left. The British used to be brilliant taxonomists. Now our treasure house of diversity – the Natural History Museum – is forced to devote much of its effort to scientific video games and to mission statements, The systematic study of life is, in Britain, as endangered as are the species themselves. Much of ecology, too, has turned itself into a pallid version of molecular biology.

Wilson has other prescriptions for the future. Habitats – rather than species – must be preserved, and the monetary value of the forest fully realised by those who exploit it. What is more, we must recognise the value, if need be in brutal economic terms, of humanity’s desire to experience nature. His book is a passionate defence of life’s variety written, at its best, in the dispassionate terms of a master of scientific ecology. Who knows? After having read it, I might even watch the next Survival programme to the end.

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Vol. 15 No. 11 · 10 June 1993

In his review of E.O. Wilson’s book The Diversity of Life, Steve Jones (LRB, 22 April) comments on the strangely large number of cichlid fish species in Lake Victoria. He appears to dismiss what he calls the conventional explanation that they arose in a multiplicity of small lakes left when the major body dried up. Perhaps it would be wise here to recall the now well-founded proposition that some 5 to 6 million years ago the Mediterranean basin was a salt desert some 3000m below sea level. The data was established by the Deep Sea Drilling Programme. Have comparable investigations been attempted in Lake Victoria? The discovery of the drying out of the Mediterranean allowed biologists to understand why the land plants and freshwater faunas of its islands seemed to have dispersed from a common origin within it.

Robin Nicholson

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