The sixth mass extinction to affect life on Earth.

All the creatures we share the Earth with are important in some way, however unprepossessing or insignificant they may appear. They and we are all part of the web of life.

From the dawn of time, extinction has usually progressed at what scientists call a natural or background rate. Today the tempo is far faster.

Many scientists believe this is the sixth great wave - the sixth mass extinction to affect life on Earth.

We were not here for any of the previous mass extinctions, but this time our sheer preponderance is driving the slide to oblivion.

We have more than doubled our numbers in half a century, and that is the most obvious reason why there is less room for any other species.

We are taking their living room to grow our food, their food to feed ourselves. We are exploiting them, trading in them, squeezing them to the margins of existence - and beyond.

Often the choice is hard: conserve a species or feed a community, tourists' dollars or turtles' nests.

In 2003 the World Conservation Union's Red List said more than 12,000 species (out of 40,000 assessed) faced some extinction risk, including:

• one bird in eight
• 13% of the world's flowering plants
• a quarter of all mammals.

That gives you a ballpark figure. Science has described 1.75 million species, some experts estimate that there may be 13 or 14 million in the world in total - but until they are catalogued, nobody knows.

Our pillage of the natural world has been likened to burning down the medieval libraries of Europe, before we had even bothered to catalogue their contents.

Many species keep us alive, purifying water, fixing nitrogen, recycling nutrients and waste, and pollinating crops.

Plants and bacteria carry out photosynthesis, which produces the oxygen we breathe. Trees absorb carbon dioxide, the main greenhouse gas given off by human activities.

Pandas and microbes

Some years ago, when the global annual gross product was about $18 trillion, US researchers calculated the value of the goods and services provided by the Earth to the world economy: $33 trillion.

Tropical cone snails contain toxins which show promise for treating some forms of cancer and heart irregularities. One toxin may be a thousand times more potent than morphine for pain relief.

But millions of cone snails are now killed annually for their shells, and their habitats are under pressure.

That is the argument for utility. But the creatures we can see, and those we can use directly, are just the start of the story.

Lord May, president of the Royal Society (the UK's national academy of sciences), has said: "Most conservation effort goes into birds and mammals - creatures like the panda, a dim, dead-end animal that was probably on the way out anyway.

"Yet arguably it's the little things that run the world, things like soil microbes. They're the least-known species of all."

Complex network

And we continue to tug at the loose threads of the web of life, thinking we can split it into its separate parts.

Brazil nuts are a lucrative harvest in the Amazon. But an experiment to produce them in plantations failed, because the trees bear a good crop in the forest, but are barren in isolation.

We are not removing individual species from the Amazon: we are destroying the entire forest.

US researchers estimate that by 2020 less than 5% of it will remain in pristine condition.

Within 15 years, about a fifth of central Africa's forests will have gone, by one estimate. And the forests of Indonesia are in headlong retreat.

Some species are bucking the trend towards extinction. In 1953 there were about 2.5bn people: today there are 6bn.

Ensuring other species keep their living space is not sentimental. It is the only way we shall survive.

Extinction, whatever Steven Spielberg says, really is for ever.

The web is unravelling...

Planet Under Pressure -- BBC News