Why are we asking this now?
Yesterday, a species of freshwater dolphin found only in the Yangtze river in China was declared extinct. Called the baiji, meaning white flag in Chinese, the Yangtze river dolphin had a pale skin and distinctive long snout and had been found in the river for more than 20 million years.

How can we be sure the Yangtze river dolphin is extinct?
We can't - but the evidence is very strong. The last confirmed sighting was in 2002 when it was photographed. An intensive six-week search of the river last December by two boats manned by scientists failed to find any. The river is its only natural habitat, all of which could be explored. Led by Dr Samuel Turvey, conservation biologist of the Zoological Society of London, the report of the expedition appeared in the journal of the Royal Society, Biology Letters, yesterday.

Why is there not one in a zoo?
There was. Qi Qi lived in an aquarium in Wuhan, a port on the Yangtze, but died of old age at 22 in 2002. The baiji were never successfully bred in captivity. Last December's expedition was to rescue any of the dolphins found and remove them to an oxbow lake for an intensive breeding programme. But the scientists were too late.

There are lots of species of dolphins - why does the loss of this one matter?
Ecosystems are potentially like houses of cards. The Yangtze has lost its top predator. That shows clearly that the ecosystem is in a state of collapse. It has implications not only for the welfare of other river creatures but also for human welfare and survival. One tenth of the world's population live in the Yangtze basin and it is human activity - shipping and fishing - that appears to have destroyed the baiji.

Isn't extinction part of evolution?
Yes. A glance at the fossil record shows how countless species have disappeared over millennia to make room for rival species. But the extinctions that are happening now are far ahead of what has happened before and they are occurring for no meaningful evolutionary reason. We are experiencing a mass extinction event driven by human activity.

What is different about what is happening now?
Extinction has taken place over evolutionary time - a timespan of thousands to millions of years. Now the process has been speeded up and is taking place over ecological time - a timespan of hundreds to thousands of years - driven by accelerating change in the environment. Like rivets falling off the wing of a plane, we don't know which is the crucial one that is going to bring the plane down.

Haven't we had mass extinctions before?
Yes. The best known is the one that wiped out the dinosaurs. But the Yangtze river dolphin is the first to be driven by human activity. No one would consider destroying the Mona Lisa or Machu Picchu. They are part of our global heritage. Yet that is just what we are allowing to happen in the natural world.

Besides the species itself, do we lose anything else?
Yes. We lose any potential it offers to help us. To take one example, the Madagascar periwinkle is being investigated by scientists developing anti-cancer drugs as a possible treatment for leukaemia. But it is a plant in perilous decline. If it disappears, so will leukaemia sufferers' hopes.

Do 'extinct' species ever reappear?
Yes. The most famous example was the coelacanth, a primitive fish pre-dating the dinosaurs, which was thought to have been wiped out 65 million years ago - well before those massive creatures met their demise. That was until a trawler hauled one up in its nets off the port of East London in South Africa on 23 December 1938. The existence of a thriving coelacanth population was later established.

What British species are threatened with extinction?
Too many to mention them all, but a few examples are: the snowy owl, an arctic species that used to nest here but stopped doing so in 1975; the greater horseshoe bat, the rarest of our 17 bat species, driven out by changes in farming and the reduction in insects; ptarmigan, the only British birds to turn completely white in winter (not helpful in a world of disappearing snow); and the wood white, a delicate butterfly that thrives in "edge" habitats such as open rides through woodland.

As extinctions go, how important is the loss of the baiji?
Very. It is the first large animal to go extinct for 50 years since the disappearance of the Caribbean monk seal, which lived in remote areas of the Caribbean and was last seen in 1952. They had been hunted since the time of Columbus for food and oil. Like many other species, they were destroyed by us.

Is that all?
No. The baiji separated from all other species so many millions of years ago, and had become so distinct, that it qualified as a mammal family in its own right. It is only the fourth entire mammal family to disappear since the time of Columbus, when Europeans began their colonisation of the world. Dr Turvey described it as the "disappearance of a complete branch of the tree of life".

What were the other major extinctions of the past 500 years?
The three previous mammal families gone from the face of the Earth are the giant lemurs of Madagascar, eliminated in the 17th century, the island shrews of the West Indies, probably wiped out by rats that accompanied Colombus, and the Tasmanian tiger, the last known specimen of which died in captivity in 1936. (The most famous creature to have become extinct in the past 500 years, the dodo, was a bird.)

Are there any other reasons to mourn the loss of the baiji?
The reason people like Dr Turvey do the work that they do is because they believe threatened species - mostly threatened by us - have as much right to be on this Earth as we do. We have no right to destroy them in the drastic way that we are doing so, he says. "If our only legacy is a dead planet, what does that say about us as a species?"

Does the loss of a species such as the Yangtze river dolphin matter?

Yes...
* It shows that the ecosystem of the Yangtze river is in a state of collapse
* It reveals the destructive effect that human activity is having on the natural world
* It serves as a wake-up call for us to take immediate action to prevent the loss of other species

No...
* Countless species have disappeared over millennia as a result of competition from rival species
* Mass extinctions have occurred before, and the last one wiped out the dinosaurs
* We can't be sure the river dolphin has gone - and it is possible that it will reappear

(By Jeremy Laurance, The Independet, 09/08/2007)