Samuel Turvey, BBC Green Room 23 Feb 10;
Once species disappear from the face of the Earth, they are quickly forgotten, says Samuel Turvey. In this week's Green Room, he warns that extinctions must be treated as a warning that human activities, such as overhunting and agriculture, are making the planet a poorer place to live.
It has been widely reported that the Earth's species are facing a sixth mass extinction and that human activity is to blame.
What is less well known is that humans have also been responsible for causing species extinctions throughout history and recent pre-history.
In the British Isles, we have lost most of our native large animals as a direct result of overhunting and the way humans changed habitats.
How many people living in the UK would consider lynx, wolves, or pelicans to be part of their native fauna, though? We have no direct cultural memory of any of these species ever being part of the British environment.
Sooner or later, communities will inevitably forget about the former existence of species that used to occur in their environment.
Local perceptions of past ecological conditions are expected to change over time, as older community members die and younger members become adults, because accurate information is unlikely to be passed down from generation to generation.
Over time, more and more degraded environmental conditions may therefore be seen as "normal". This social phenomenon is called "shifting baseline syndrome".
The existence of shifting baseline syndrome has been widely discussed and debated. However, few studies have investigated the rate at which communities can forget about environmental changes in the recent past.
Missed opportunities
This is particularly important for conservation because often environmental knowledge from local communities is the only information available to assess the status of rare species, or to reconstruct recent extinctions and environmental change.
For example, interviews with Aboriginal people in the central deserts of Australia have revealed that native mammals such as the pig-footed bandicoot, previously thought to have died out in the early part of the 20th Century, actually survived until at least the 1950s.
But just as human-caused species extinctions continue to occur, the true level of our impact on the environment also continues to be forgotten.
The most significant recent extinction was the disappearance of the Yangtze River dolphin, or baiji; the first large mammal to be wiped out in more than 50 years.
Once revered as a reincarnated princess, this species experienced a severe population decline throughout the late 20th Century, mainly as a result of unsustainable levels of accidental dolphin deaths in fishing gear.
Despite repeated pleas for international conservation intervention, by the late 1990s only about 13 animals were thought to survive.
I participated in the range-wide baiji survey in 2006 that failed to find any evidence of surviving dolphins in the Yangtze. In 2007, we declared the species to be probably extinct.
The loss of the baiji is only part of the massive-scale environmental degradation of the Yangtze.
Until recently, the river was also home to the Yangtze paddlefish, the largest freshwater fish in the world - mature adults could reach lengths of seven metres.
The paddlefish used to be caught commercially in the Yangtze, but overfishing and dam construction caused the population to collapse, and only three individuals have been caught in the past decade. The species may now already be extinct.
These factors also led to the disappearance of Reeves' shad, the basis of another Chinese commercial fishery until the 1980s.
In 2008, I returned to the Yangtze region as part of a wide-range interview survey of fishing communities.
We were interested in trying to find out if local fishermen, who spend much of their time on the river, might know of the existence of any surviving baiji. Sadly, we found little evidence to suggest that there were any baiji left in the river.
As we conducted our interviews though we did make a surprising discovery.
Older people told us all about the historical declines of baiji, paddlefish and shad, how often these species were seen and caught in the past, and even what they tasted like.
However, younger fishermen from the same communities had not only never seen baiji or paddlefish, but had never even heard of them.
These distinctive species - a dolphin and a giant fish - had only died out a few years earlier, and had been culturally and commercially important in the recent past, but already local knowledge about them was disappearing very rapidly.
We estimated that more than 70% of fishermen below the age of 40, or who first started fishing after 1995, were completely unaware of what a paddlefish was.
Our findings suggest that as soon as even "megafaunal" species stop being encountered on a fairly regular basis, they immediately start to become forgotten. They are truly "out of sight, out of mind".
It is the final insult for the baiji - not only was the species allowed to die out, forgotten by the conservation community until it was too late, but it is now being forgotten, even in China.
Conservation in the Yangtze remains an urgent priority. Although the baiji, shad and paddlefish are now all probably gone, other species such as the Yangtze finless porpoise are also in imminent danger of extinction.
But will we manage to act in time to save the porpoise? Or will this species, and many others, also become completely forgotten?
Dr Samuel Turvey is a research fellow for the Zoological Society of London (ZSL)
The Green Room is a series of opinion articles on environmental topics running weekly on the BBC News website
