The world has experienced many periods of mass extinction caused by a variety of natural factors, but the greatest period of mass extinction the world has ever seen is occurring right now.

It is reckoned that the current rate of extinction is between a hundred and a thousand times faster than the average historical extinction rate for the planet.

The current period of extinction is known as the Holocene extinction event, sometimes referred to as the sixth extinction, as there have been five distinctive periods of mass extinction previously.

Scientists estimate that during the last century between 20,000 and two million species have become extinct. However, the observed rate of extinction has accelerated dramatically in the last 50 years, linked almost exclusively to the activities of human beings.

Some experts have estimated that up to half of presently existing species may become extinct by 2100.

What is Extinction?

The moment of extinction is generally considered to be the death of the last individual of that species, but in reality a species may be, to all intents and purposes, extinct long before that. The destruction of a habitat, the sudden shrinkage of a population or the absence of a breeding pair can all signal the functional extinction of a species.

Extinction is an entirely natural part of life. Charles Darwin noted that the fittest species survived, out-competing the rest and condemning them to extinction. Typically a species becomes extinct within 10 million years of its first appearance. It is estimated that 99.9% of all species that have ever lived are now extinct. What is unique about the current extinction rate is the speed of the loss and the unique role of one species in seeing off the rest.

The IUCN (International Union of Conservation of Nature) Red List of Threatened Species is the world's most comprehensive inventory of the global conservation status of plant and animal species. The IUCN Red List uses precise criteria to evaluate the extinction risk of thousands of species.

Species are classified in nine groups:

Extinct

Extinct in the Wild

Critically Endangered

Endangered

Vulnerable

Near Threatened

Least Concern

Data Deficient

Not Evaluated

When a species is defined as 'threatened', which includes most of the species featured in Last Chance to See, it falls into one of the three groups - Critically Endangered (e.g. Orangutans), Endangered, (e.g. Aye-aye) and Vulnerable to Extinction (e.g. Amazonian Manatee).

The Situation Today

Life on Earth is disappearing with species hurtling towards extinction at an unprecedented rate.

There are currently so many threatened species that if we made a film about each one of them, and broadcast one film every week, the series would run for well over 300 years without a break.

One in four mammals, one in eight birds and one in three amphibians now appear on the Red List.

Human activity causing loss of habitat through urbanisation, agriculture and deforestation combined with climate change is widely agreed to be the biggest threat to species survival.

There are now 41,415 species on the Red List and 16,306 are threatened with extinction, up from 16,118 last year.

Figures correct at time of publication (Autumn 2008)

Where there's life...

Last Chance to See is not just a search for animals on the edge of extinction, it is also a celebration of conservationists. Across the world thousands of individuals spend their time, often their lives, in some of the harshest places on earth, generally on very little pay, in an effort to help a species pull back from the brink.

In 1980 the New Zealand Black Robin was the rarest bird in the world with just five individuals remaining. Don Merton committed himself to doing whatever he could to save the species. Today there are over 250.

All over the world, individuals are making a difference and scoring significant victories.

People have caused the problem and only people can provide the solution through conservation work, through the choices they make and the pressure they put on politicians.

Animals on the Edge

Some of the best known species currently facing extinction (in 2008-09) are:

Tigers There are now thought to be fewer than 5,000 tigers in the wild, living in increasingly fragmented forests. Major threats facing tigers are poaching, habitat destruction, and the use of tiger body parts in traditional Chinese medicines.

There are now thought to be fewer than 5,000 tigers in the wild, living in increasingly fragmented forests. Major threats facing tigers are poaching, habitat destruction, and the use of tiger body parts in traditional Chinese medicines. Polar bears

Giant pandas There may only be 1,600 pandas left in the wild. China's human population explosion has led to the rapid destruction of bamboo forests to make way for roads and agricultural land. This has left isolated pockets of forest for pandas to live.

There may only be 1,600 pandas left in the wild. China's human population explosion has led to the rapid destruction of bamboo forests to make way for roads and agricultural land. This has left isolated pockets of forest for pandas to live. Orangutans In the last 100 years, 80% of orangutans have been wiped out, with fewer than 60,000 remaining. Deforestation - to supply both the timber and palm oil trade - is the major threat facing orangutans. Palm oil is used in a wide range of food and toiletries.

In the last 100 years, 80% of orangutans have been wiped out, with fewer than 60,000 remaining. Deforestation - to supply both the timber and palm oil trade - is the major threat facing orangutans. Palm oil is used in a wide range of food and toiletries. Leatherback turtles More than 90% of Pacific leatherbacks have disappeared in the last 20 years. Just 2,300 adult females are now left. Turtles are under threat from accidental capture by long line fishing. Turtle eggs are considered to be aphrodisiacs in some parts of the world and adult turtles are often killed for their meat.

More than 90% of Pacific leatherbacks have disappeared in the last 20 years. Just 2,300 adult females are now left. Turtles are under threat from accidental capture by long line fishing. Turtle eggs are considered to be aphrodisiacs in some parts of the world and adult turtles are often killed for their meat. Asian elephants Destruction of forests for farming and housing in the last 30 years has caused the loss of more than half of the world's elephants. Only 30,000 Asian elephants now survive in the wild.

The Weird and the Wonderful

Talk about extinction and these are the animals which are mentioned most. They are the great creatures that fill the rugged landscapes of our childhood imagination and the idea that they might vanish is almost too ghastly to contemplate. But Douglas Adams and Mark Carwardine knew, even in 1988, that the plight of these beasts was so well known that a new adventure to track them down was unlikely to get much attention. They wanted to go in search of animals that were, frankly, odd. Douglas and Mark set out to trawl the world in search of the weird and wonderful in the hope that their adventures might inspire others to take an interest in the plight of species around the world. Among the creatures they set out to find were:

The Komodo Dragon, a giant lizard with saliva so toxic that a single bite can kill a man.

The Aye-aye, a strange gremlin-like lemur widely believed, in the villages of Madagascar, to be a bringer of death.

The Kakapo, a large fat flightless parrot living in New Zealand.

The Northern White Rhino, a vast rhinoceros which is not white.

The Amazonian Manatee, a large fat mammal living under the murky waters of the Amazon.

Douglas Adams and Mark Carwardine embarked on a series of ambitious, occasionally chaotic and sometimes entirely unsuccessful adventures. The story of their journeys to the furthest ends of the world in search of the decidedly weird and the indisputably wonderful, both on radio and in their book, is as funny, engaging and thought provoking today as it was 20 years ago when it was written.