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.
Just as human-caused species extinctions continue to occur, the true level of our impact on the environment also continues to be forgotten
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.
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.
As soon as even 'megafaunal' species stop being encountered on a fairly regular basis, they immediately start to become forgotten
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
Do you agree with Dr Turvey? Should more be done to protect endangered species and habitats? Are you concerned that each generation views the state of a degraded environment as the norm? Does more need to be done to ensure that we learn lessons from past mistakes?
As a South Asian I am giving Dr Turvey a lot of thanks for his excellent story. I am completely agreed with his concepts. I born in a village of Kushtia in Bangladesh in 1964. At the time of my childhood I have seen many "Shushuk"/ black Dolphin in our river Gorai. I have seen a lot of jungle cat in jungle adjacent our house, varieties type of Bird and fish. But, now days, I see nothing of them. They were disappeared due to the over population. People established there residential and commercial area. A little numbers are existed but which is under threat. So, we should be more careful to protect such endangered species and habitats.
Engr Salam, LGED Bhaban, Dhaka, Banladesh
Abundance and pace of human numbers and their activity is the primary cause of everything. Extinction of habitat and species is the result of abundance of human activities. We need to change the definition and perception of the words like 'Civilization' 'Growth' and 'Development'. Forest and Natural lakes have become more important than the highways. The Eagles, Kingfishers, Butterflies are equally important like human beings. Though natural system is speech less but we should not forget that it's a perfect, impeccable and precise system. It has got its own rules.
Sanjay Singh Thakur, Indore,India
Yes I do,but big business interests often see wildlife as an obstacle.The Tasmanian Wolf or Thylacine,thought extinct in the 1930's may still exist in small numbers,there have been many alleged sitings etc.since.Tasmania is now being ravaged by logging companies,would the loggers want living Thylacines to surface now?
steve johnson, whitwick, leics
Concerning the "shifting baseline syndrome", I would like to point out that, from a cultural point of view, it is interesting to note that the opposite also occurs - societies take with them the memories of animals when they arrive in a new territory, and preserve such memory for an amazing length of time: Although bears never made it into Ireland after the last ice age, the celtic tribes settling there preserved the word for this animal and kept it in their lores. Thus, whether or not an animal stays in the memory does not primarily depend on its visibility, but rather its integration into the society's culture. In this respect, fish might be doubly disadvantaged in making it into a society's consciousness, as they are mute and hard to see in the first place.
Frank Weise, Tuebingen, Germany
By any means these animals should be rescued. However, I remain sceptical of the UK's commitment to preserving and restoring the wild things in its own backyard. I think it perverse that the UK has so many "experts" to offer the world of conservation and deeply disappointing, too.
William Barkley, Southgate,USA
Oh, I certainly agree with Dr Turvey. The wild boar was also common in England once. In more recent times, how many have seen a speedwell bluebell? In New Zealand, the Moa and the Haast Eagle (amongst the largest birds to have ever lived) exist only in the memories of museum addicts. The West African Black Rhino was reported extinct by the BBC website recently, but didn't even make the "see also" links.
Jonathan Day, Portland, Oregon, USA
Dr Turvey is, sadly, quite right. If one needs another example of human forgetfulness, one only need turn to our own history. How many implements of past times go unrecognised today, unless they are labelled as what they are in some museum? How much is forgotten in small places, where it seems quite unimportant to record anything? How many people know anything about dress in, say, 1754 or 1817, or even 1922?
D. Fear, Heidelberg, Germany
I absolutely agree. Humans have always been predators - it's in our nature - but a responsible predator remains in balance with its prey species.
The ecological baseline which Dr Turvey refers to should be set right back to the last Ice Age: any environment lacking its original range of megafaunal species can be considered degraded, which includes every landmass except Africa and southern Asia. It is generally agreed that humans were at least partly reponsible for wiping out the large Pleistocene animals; the least we can do today is avoid exterminating the Earth's remaining wildlife. Many Americans would love to restore depopulated areas of the USA to its pre-colonial wilderness state, yet even that was a zoologically impoverished land.
On a positive note, it is encouraging to think that while our Stone Age ancestors, with their low numbers and primitive weapons, killed off over a dozen species of elephants, the teeming hi-tech humans of today have yet managed to preserve the 3 surviving elephant species.
Ultimately, if there is no way to maintain an animal in the wild, captive breeding populations must be sustained, and genetic samples must be frozen and stored - in the hope of reintroducing them at some far future time.
Nicholas Wordsworth, Leeming, UK
I was surprised to learn that pelicans had once lived in the UK, since that's where I grew up and its a very strange concept to me, the lynx too.
It's sad to see a species die out, but even sadder to see it forgotten. I followed the river dolphin from when it hit the endangered list, when i was a young girl, to the announcement that its probably extinct a few years ago. It saddens me immensely that species can be driven to extinction and then forgotten so easily by the race that caused it.
I hope attitudes change in the future, but some cynical part of me tells me that hope is futile.
Fingers crossed the world proves me wrong.
Chloe, NSW, Australia
Your report highlight the issue of preservation of nature basic characteristics..The forest land and natural lakes have been converted into highways. Even the common found Eagles which we used to see in sky during childhood have vanished. The kingfishers are now rare to be seen sitting on a lonely electric pole. Flowers are less surrounded by butterflies now. We are living in a world ,where now, the geographies on the earth are changing at rapid pace. We have designed equipments which are capable of making tunnels into sea in no time, similarly cutting a natural mountain and making a sky high concrete structures. Man has no space to live in some part of earth, they are destroying nature and speech less species. We must forget economy now and concentrate on existence and survival for all.
Surendra Singh, India