Science: Going before their time

There may be more species alive now than at any time in the history of life on Earth, but they are dying off at an alarming rate. And there's one species in particular that's to blame - Homo sapiens.

We are on the cusp of a unique period in the history of life on Earth when species are becoming extinct at a rate something like 10,000 times greater than they would be under normal circumstances. "This represents the sixth great wave of extinction, fully compatible with the big five mass extinctions of the geological past, but different in that it results from the activities of a single other species rather than from external environmental changes," according to Sir Robert May, the government's chief scientific adviser.

The destructive species Professor May had in mind when he addressed the 50th anniversary meeting of The World Conservation Union last November in Fontainebleu was, of course, Homo sapiens. Man's activities, notably his ruthless destruction of natural habitats and ever-growing consumption of the Earth's limited resources, will put thousands of species at risk of extinction over the next century. The problem scientists face is trying to assess the likely scale of the problem.

Few scientists who have studied the destruction of the planet's biodiversity - a measure of the wealth of animals and plants alive today - are in any doubt that we are facing another mass extinction. The difficulty, however, is proving it. There is no dispute over the scale of habitat destruction over the past few centuries, but how do we know that this has resulted in the extinction of species?

The recorded extinctions since 1600 of all types of animals, from molluscs to mammals, amount to no more than about 1,000 species, which is a tiny fraction of the many millions of species of animals and plants alive today. Sceptics also point out that the forest cover of the eastern United States now amounts to just 1 or 2 per cent of its original extent, yet only three forest birds went extinct during that period.

Georgina Mace, an expert on species extinction at the Institute of Zoology in London, says that such an interpretation underplays the true nature of the problem. "Many species go extinct unnoticed; some have never been described and some have been described but are so poorly known that we would not notice their passing," she says. It is a well-known phenomenon in biology - the more a group of animals or plants is studied, the greater the threat of extinction is realised.

Another reason why the problem can be easily underestimated is that the rules governing what is extinct are quite strict. The animal or plant in question must not have been observed for more than 50 years. Many species may be extinct already but not yet fulfilled the criteria of a recognised extinction. As Dr Mace points out, it is always harder to prove something does not exist than to show it does exist.

A central difficulty in assessing the scale of current extinction rates is that biologists have only formally described and named a fraction of the planet's lifeforms. Professor May and John Lawton, director of the Centre for Population Biology at Imperial College London, say that about 1.5 million species of animals and plants have names, but the total number of species could range from five million to 15 million. Furry and feathery animals are well described, but the same cannot be said for insects, worms and other "lower" lifeforms.

Ed Mathew, a campaigner with the World Wide Fund (WWF) for Nature says ignorance is the biggest problem. "To monitor the situation we need good information about the world's species. This information does not exist. Species are being destroyed faster than they are being described," he says.

Scientists estimate that the present biodiversity on Earth is so rich that it means there are more species alive now than at any other single period in the history of life. And yet, the millions of species living today constitute less than about 4 per cent of the total number of species that have existed during the past 600 million years following the "explosion" of the diversity of life during the Cambrian period. Extinction is an inevitable result of natural selection, which actually brings about new species in the continuing process of evolution.

Scientists have attempted to estimate the speed of the "background" extinction rate which must be taking place all the time, without the influence of human activity. They looked at what has happened in the past by studying extinction rates estimated from the fossil record, extending back over many hundreds of millions of years. This suggests that a typical lifetime of a species - from when it originated as a distinct interbreeding entity, to its final demise and removal - is a few million years. Some species, such as insects which last on average about five to 10 million years, have a longer lifetime than others, notably mammals which typically survive as a single species for about two million years.

When May and Lawton looked at extinction rates today, based on known extinctions of a species within a single group, say birds or mammals, they found that typical species lifetime was significantly shorter - about 10,000 years. "This may sound a long time, but the estimate for birds and mammals is 100 to 1,000 times shorter than the lifetimes of species in the fossil record," says Dr Mace.

Another method of estimating extinction looks at the destruction of natural habitats. The WWF says in its Living Planet Report published last year that the world's forest cover has decreased by 13 per cent between 1960 and 1990, which is equivalent to losing an area half the size of Norway each year. Scientists such as Brian Groombridge of the World Conservation Monitoring Centre in Cambridge are attempting to work out how this habitat loss is impinging on biodiversity.

A rule of thumb - and it is rough because different habitats carry different densities of animals and plants - is that a 90 per cent decrease in the area of natural vegetation will result in the loss of between 30 and 55 per cent of species. This means, for example, that if tropical forests are being lost at a rate of between 0.8 per cent and 2 per cent a year, the corresponding loss of species would amount to an annual loss of between 0.2 and 0.5 per cent of the total. "If there are five million species, then 10,000 to 25,000 species are committed to extinction each year as a result of habitat loss," says Dr Mace.

These figures tie in quite well with those based on the known loss of individual species within well studied groups. They also match the rapid loss seen during the five mass extinctions of evolutionary history. Dr Mace reaffirms the view of colleagues such as May, Lawton and Groombridge: "We do seem to be on the brink of a largescale extinction spasm, but a major difference is that now almost all extinctions are due directly or indirectly to the impact of human activities. People now so dominate the Earth that there are very few species completely unaffected by our existence."

John Lawton puts is more starkly: "Whatever view one takes, the impending sixth mass extinction will be unique in the history of the planet."

Suggested Topics
Arts and Entertainment
Saw point: Bradley Cooper and Jennifer Lawrence in ‘Serena’
film
Arts and Entertainment
Taylor Swift performs at the 2014 iHeart Radio Music Festival
musicReview: 1989's songs attempt to encapsulate dramatic emotional change in a few striking lines
Arts and Entertainment
Paul Anderson plays Arthur Shelby in Peaky Blinders series two
tvReview: Arthur Shelby Jr seems to be losing his mind as his younger brother lets him run riot in London
Arts and Entertainment
Miranda Hart has called time on her award-winning BBC sitcom, Miranda
tv
Arts and Entertainment
Sir Nicholas Serota has been a feature in the Power 100 top ten since its 2002 launch
art
PROMOTED VIDEO
Arts and Entertainment
Boy George performing with Culture Club at Heaven

musicReview: Culture Club performs live for first time in 12 years

Arts and Entertainment
Laura Wood, winner of the Montegrappa Scholastic Prize for New Children’s Writing
books

Children's bookseller wins The Independent's new author search

Have you tried new the Independent Digital Edition apps?
Arts and Entertainment
Pulling the strings: Spira Mirabilis

music
Arts and Entertainment
Neville's Island at Duke of York's theatre
musicReview: The production has been cleverly cast with a quartet of comic performers best known for the work on television
Arts and Entertainment
Banksy's 'The Girl with the Pierced Eardrum' in Bristol

art
Arts and Entertainment
Lynda Bellingham stars in her last Oxo advert with on-screen husband Michael Redfern

tv
Arts and Entertainment
Hunger Games actress Jena Malone has been rumoured to be playing a female Robin in Batman v Superman

film
Arts and Entertainment
Tim Minchin portrait
For a no-holds-barred performer who is scathing about woolly thinking and oppressive religiosity, Tim Minchin is surprisingly gentle
Arts and Entertainment
Clara takes the lead in 'Flatline' while the Doctor remains in the Tardis
tvReview: The 'Impossible Girl' earns some companion stripes... but she’s still annoying in 'Dr Who, Flatline'
Arts and Entertainment
Joy Division photographed around Waterloo Road, Stockport, near Strawberry Studios. The band are Bernard Sumner (guitar and keyboards), Stephen Morris (drums and percussion), Ian Curtis (vocals and occasional guitar), Peter Hook (bass guitar and backing vocals).
books
Arts and Entertainment
Sean Harris in 'The Goob' film photocall, at the Venice International Film Festival 2014
filmThe Bafta-winner talks Hollywood, being branded a psycho, and how Streisand is his true inspiration
Arts and Entertainment
X Factor contestant Fleur East
tvReview: Some lacklustre performances - but the usual frontrunners continue to excel
Arts and Entertainment
Richard Tuttle's installation in the Turbine Hall at the Tate Modern
artAs two major London galleries put textiles in the spotlight, the poor relation of the creative world is getting recognition it deserves
Arts and Entertainment
Hunger Games actress Jena Malone has been rumoured to be playing a female Robin in Batman v Superman
film
Arts and Entertainment
On top of the world: Actress Cate Blanchett and author Richard Flanagan
artsRichard Flanagan's Man Booker win has put paid to the myth that antipodean artists lack culture
Arts and Entertainment
The Everyman, revamped by Haworth Tompkins
architectureIt beats strong shortlist that included the Shard, the Library of Birmingham, and the London Aquatics Centre
Arts and Entertainment
Justice is served: Robert Downey Jr, Vincent D’Onofrio, Jeremy Strong and Robert Duvall in ‘The Judge’

Film

Arts and Entertainment
Clive Owen (centre) in 'The Knick'

TV

Arts and Entertainment
J.K. Simmons , left, and Miles Teller in a scene from

Film

Latest stories from i100
Have you tried new the Independent Digital Edition apps?

ES Rentals

    Independent Dating
    and  

    By clicking 'Search' you
    are agreeing to our
    Terms of Use.

    Wilko Johnson, now the bad news: musician splits with manager after police investigate assault claims

    Wilko Johnson, now the bad news

    Former Dr Feelgood splits with manager after police investigate assault claims
    Mark Udall: The Democrat Senator with a fight on his hands ahead of the US midterm elections

    Mark Udall: The Democrat Senator with a fight on his hands

    The Senator for Colorado is for gay rights, for abortion rights – and in the Republicans’ sights as they threaten to take control of the Senate next month
    New discoveries show more contact between far-flung prehistoric humans than had been thought

    New discoveries show more contact between far-flung prehistoric humans than had been thought

    Evidence found of contact between Easter Islanders and South America
    Cerys Matthews reveals how her uncle taped 150 interviews for a biography of Dylan Thomas

    Cerys Matthews on Dylan Thomas

    The singer reveals how her uncle taped 150 interviews for a biography of the famous Welsh poet
    DIY is not fun and we've finally realised this as a nation

    Homebase closures: 'DIY is not fun'

    Homebase has announced the closure of one in four of its stores. Nick Harding, who never did know his awl from his elbow, is glad to see the back of DIY
    The Battle of the Five Armies: Air New Zealand releases new Hobbit-inspired in-flight video

    Air New Zealand's wizard in-flight video

    The airline has released a new Hobbit-inspired clip dubbed "The most epic safety video ever made"
    Pumpkin spice is the flavour of the month - but can you stomach the sweetness?

    Pumpkin spice is the flavour of the month

    The combination of cinnamon, clove, nutmeg (and no actual pumpkin), now flavours everything from lattes to cream cheese in the US
    11 best sonic skincare brushes

    11 best sonic skincare brushes

    Forget the flannel - take skincare to the next level by using your favourite cleanser with a sonic facial brush
    Paul Scholes column: I'm not worried about Manchester United's defence - Chelsea test can be the making of Phil Jones and Marcos Rojo

    Paul Scholes column

    I'm not worried about Manchester United's defence - Chelsea test can be the making of Jones and Rojo
    Frank Warren: Boxing has its problems but in all my time I've never seen a crooked fight

    Frank Warren: Boxing has its problems but in all my time I've never seen a crooked fight

    While other sports are stalked by corruption, we are an easy target for the critics
    Jamie Roberts exclusive interview: 'I'm a man of my word – I'll stay in Paris'

    Jamie Roberts: 'I'm a man of my word – I'll stay in Paris'

    Wales centre says he’s not coming home but is looking to establish himself at Racing Métro
    How could three tourists have been battered within an inch of their lives by a burglar in a plush London hotel?

    A crime that reveals London's dark heart

    How could three tourists have been battered within an inch of their lives by a burglar in a plush London hotel?
    Meet 'Porridge' and 'Vampire': Chinese state TV is offering advice for citizens picking a Western moniker

    Lost in translation: Western monikers

    Chinese state TV is offering advice for citizens picking a Western moniker. Simon Usborne, who met a 'Porridge' and a 'Vampire' while in China, can see the problem
    Handy hacks that make life easier: New book reveals how to rid your inbox of spam, protect your passwords and amplify your iPhone

    Handy hacks that make life easier

    New book reveals how to rid your email inbox of spam, protect your passwords and amplify your iPhone with a loo-roll
    KidZania lets children try their hands at being a firefighter, doctor or factory worker for the day

    KidZania: It's a small world

    The new 'educational entertainment experience' in London's Shepherd's Bush will allow children to try out the jobs that are usually undertaken by adults, including firefighter, doctor or factory worker