THE MOST reliable guess that scientists have ventured about the origin of the universe is that it was the result of a cosmic explosion that took place about 25 billion years ago. Before the explosion, all matter in the universe is believed to have existed as a highly condensed cosmic egg. The so-called "big bang", say scientists, sent the matter from the cosmic egg hurtling into the universe to form a countless number of stars.

Several stars form a galaxy. And galaxies themselves are clustered into groups. Our own cluster, consisting of about 25 galaxies, is called the local group and one of its galaxies is known as the Milky Way, which consists of over a hundred billion stars. The sun is one of the stars in the Milky Way and it has nine planets revolving around it, the third of which in distance from the sun is the earth. As far as is known, the earth is the only planet to possess that remarkable entity called life.

The earth was born about 4.6 billion years ago. A primitive form of life is thought to have originated on earth through complex chemical reactions about 3 6 billion years ago. These living entities, be dividing and changing, set off a chain of events that is referred to as biological evolution. For nearly 3 billion of the 3.6 billion years, life existed as microscopic blobs of protoplasm in the ocean. But about 600 ne years ago, these living organisms became larger and more diverse and, in time, developed hard skeletal structures.

Major developments in this drama were the evolution about 400 an years ago of plants and animals, which could live on land instead of water. Insects and reptiles arrived about 300 m years ago, birds and mammals about 200 m years ago and flowering plants about 50 m years later.
Evolution of Homo sapiens This gradual and relatively smooth evolution to progressively more complex forms of life received a major jolt about 2 ra years ago with the origin of a rather special lineage of primates referred to as the genus Homo. A single species of this line evolved about 40,000 years ago into Homo sapiens, displaying all the qualities of present-day human beings. Homo sapiens" qualities of intelligence and ability to manipulate the environment enabled the species to gain unprecedented mastery over other forms of life.

Indeed, Homo sapiens manipulated their physical environment to the extent that for the first time a species of living organism cut loose from the constraints of biological evolution and produced 5 billion individuals.

Unfortunately, humankind"s euphoria over its mas of the universe, its ability to increase its own life Pyectancy and its ability to genetically engineer other forms of life led it to neglect the state of the planet on which it lived.

Fortunately, the same mental qualities that enabled human beings to explore space and land on the moon, also enable them to reflect on their past, their present and their future. Perhaps, it is this quality that will prove humankind"s ultimate saviour.

over the past 25 years or so, there has been a rather sudden realisation that human beings have damaged their planet beyond recognition and perhaps beyond repair. They have destroyed the earth"s life-support systems, which evolved over billions of years, and burnt fossit fuels and decimated forests on such a large scale that temperatures on earth have increased perceptibly.

The chilling realisation that the earth cannot support humankind"s bid to grow food, provide shelter and produce consumer goods for a population whose numbers and demands are increasing is beginning to dawn on a reasonable number of people. Yet many are still unaware that every day they are destroying, perhaps by the dozens, follow living creatures, which have evolved like them.

This magnificent range of life is known by the term biodiversity, which has only roeently become fashionable and part of the vocabulary of politicians and administrators. But few are aware that even scientists know little about this biodiversity that human beings now want to save. Biodiversity - the billions of life forms that exist on earth - ranges in size from microscopic be viruses to blue whales that are more than 30 metres long. Conserving biodiversity humankind"s greatest challenge. THE MOST reliable guess that scientists have ventured about the origin of the universe is that it was the result of a cosmic explosion that took place about 25 billion years ago. Before the explosion, all matter in the universe is believed to have existed as a highly condensed cosmic egg. The so-called "big bang", say scientists, sent the matter from the cosmic egg hurtling into the universe to form a countless number of stars.

Several stars form a galaxy. And galaxies themselves are clustered into groups. Our own cluster, consisting of about 25 galaxies, is called the local group and one of its galaxies is known as the Milky Way, which consists of over a hundred billion stars. The sun is one of the stars in the Milky Way and it has nine planets revolving around it, the third of which in distance from the sun is the earth. As far as is known, the earth is the only planet to possess that remarkable entity called life.

The earth was born about 4.6 billion years ago. A primitive form of life is thought to have originated on earth through complex chemical reactions about 3 6 billion years ago. These living entities, be dividing and changing, set off a chain of events that is referred to as biological evolution. For nearly 3 billion of the 3.6 billion years, life existed as microscopic blobs of protoplasm in the ocean. But about 600 ne years ago, these living organisms became larger and more diverse and, in time, developed hard skeletal structures.

Major developments in this drama were the evolution about 400 an years ago of plants and animals, which could live on land instead of water. Insects and reptiles arrived about 300 m years ago, birds and mammals about 200 m years ago and flowering plants about 50 m years later.
Evolution of Homo sapiens
This gradual and relatively smooth evolution to progressively more complex forms of life received a major jolt about 2 ra years ago with the origin of a rather special lineage of primates referred to as the genus Homo. A single species of this line evolved about 40,000 years ago into Homo sapiens, displaying all the qualities of present-day human beings. Homo sapiens" qualities of intelligence and ability to manipulate the environment enabled the species to gain unprecedented mastery over other forms of life.

Indeed, Homo sapiens manipulated their physical environment to the extent that for the first time a species of living organism cut loose from the constraints of biological evolution and produced 5 billion individuals.

Unfortunately, humankind"s euphoria over its mas of the universe, its ability to increase its own life Pyectancy and its ability to genetically engineer other forms of life led it to neglect the state of the planet on which it lived.

Fortunately, the same mental qualities that enabled human beings to explore space and land on the moon, also enable them to reflect on their past, their present and their future. Perhaps, it is this quality that will prove humankind"s ultimate saviour.

over the past 25 years or so, there has been a rather sudden realisation that human beings have damaged their planet beyond recognition and perhaps beyond repair. They have destroyed the earth"s life-support systems, which evolved over billions of years, and burnt fossit fuels and decimated forests on such a large scale that temperatures on earth have increased perceptibly.

The chilling realisation that the earth cannot support humankind"s bid to grow food, provide shelter and produce consumer goods for a population whose numbers and demands are increasing is beginning to dawn on a reasonable number of people. Yet many are still unaware that every day they are destroying, perhaps by the dozens, follow living creatures, which have evolved like them.

This magnificent range of life is known by the term biodiversity, which has only roeently become fashionable and part of the vocabulary of politicians and administrators. But few are aware that even scientists know little about this biodiversity that human beings now want to save.

Five kingdoms
What is biodiversity? It is commonly known that the earth abounds in a spectacular range of living organisms. They are customarily classified into five "kingdoms", of which the first is protistra (bacteria and blue-green algae); the second, monera (advanced algae); third, fungi; fourth, plants; and the fifth, animals.

1iving organisms are found almost everywhere from the depths of the sea to tropical rain forests and from the polar ice-caps to hot springs. They range in size from viruses that may be no bigger than one-millionth of a metre to the African elephant, which call weigh upto 6.5 tonnes, and a redwood tree more than 100 metres tall.

A particularly surprising aspect of biodiversity is its apparent "lopsidedness". Ail overwhelming proportion of the animal biomass in tropical forests is contributed by insects (fig 1), among them, social insects such as ants and termites. In a Brazilian tropical fonst, for example, it has been. estimated that the biomass of ants is approximately four times that of all vertebrates (i.e., amphibians, reptiles, birds and mammals) put together. Few realise that in tropical forest ecosystems, the role of higher animals such as Vertebrates is "insignificant", compared to ants and other insects.

How many life forms?
Just how many kinds of living organisms are there on earth? The reply would be that"s unfortunately asking for too much. Even though human beings know all about distant galaxies and can make a reasonable guess as to how many stars there are in the universe, revertless, when it comes to estimating how many species there are on earth, human beings are at a total loss.

Even if one ignores the fact that many species are becoming extinct each day, it is not easy to record, describe or even count the number of extant species. Life, forms are so diverse that manv vears of specialised training are required to be able io"recognise and describe them and even then, such training will provide knowledge of just one small group of living organisms. Scientists have been reatiCUIOUSly riaming and describing living organisms for about 200 years. Indian taxonomists have so far named and described about 83,000 species (fig 2 ), while the total for taxonomists worldwide is about 1.8 million species (fig 3 ). From these numbers estimates were made setting the total number of species of living organisms in the world at between 5 million and 10 million.

Last biotic frontier
Then came a major jolt, for scientists at the Smithsonian Institution in Washington, DC - and in particular, T L Erwin - pointed out the insects studied were mainly from the forest floor and the forest canopy was essentially unexplored.

The tropical forest canopy the last biotic frontier - has since been carefully explored method by using a novo role of higher involving blanketing selected trees with a fog of insecticides animals such as to kill all insects and other forms of life, To everyonc."s surprise hundreds of hitherto unknown species of insects were discovered on the canopies of just a few trees in Panama.

Such richness and newness of tropical forest canopy arthropod farina has been confirmed by other Scientists such as Nigel Stork of the British Museum of Natural History. who used a similar counting technique in Borneo. All this supports the theory that the number of insect species on earth is really much larger than had been supposed. One estimate now puts their number at 30 million for arthropods alone.

Conseming biodiversity
Clearly, preserving biodiversity is the biggest challenge facing humankind. But estimating biodiversity is perhaps the greater challenge for it would require millions of man-days of painsiaking work by highly trained biologists. Nlere difficult, it would require foresight and imagination on the part of science administrators and the realisation that all this is a worthwhile exercise.

What is required is an urgent review by scientists and policy-makers an the significance of the finding that insects constitute an overwhelming proportion of animal biomass and animal species and that the total number of species of life forms may be in excess of 30 million.

How should the world"s echicaLed, enlightened citizenry respond to these rather startling findings? Should priorities be readjusted? Should taxonomists continue to catalogue new species at the present slow rate or should the 30 million arthropod species be left to their fate? Can the costs and benefits be computed? Should efforts con- tinue to catalogue, describe and conserve these species? These questions are compelling and humankind will have to address itself urgently to finding answers to them.

Raghavendro Gadagkar is director of Centre for Ecological Sciences, Indian Institute of Science.