Fish living in dark caves still feel the rhythm of life

By Leila Battison Science reporter

Millions of years of evolution in the dark have led to this Somalian cavefish losing its eyes, scales, and pigmentation.

A blind, cave-dwelling fish in Somalia knows what time it is, but its "day" is twice as long as ours.

Most animals have an internal body clock, or circadian rhythm, that lasts around 24 hours and is modified by the light-dark cycle of a day.
But an international team, whose research is published in the open access journal PloS Biology, shows that certain blind cave fish have a circadian rhythm that lasts almost two days.
The cavefish, Phreatichthys andruzzii, has evolved for nearly two million years in the isolated darkness of caves beneath the Somalian desert.
Professor Nick Foulkes, of the Karlsruhe Institute of Technology in Germany, said that this particular species was chosen "because it was such an extreme example, having been isolated from a day-night cycle for so long".
In the course of its evolution it has lost its eyes, colouration and scales, having no need for them in the pitch-black of an underground cave system.
But it appears that the absence of day and night has caused a much more profound change in the fish's life rhythm.
Light sensitivity The internal body clock of most mammals is slightly longer than 24 hours, although it is unique for each person and is modified by light.

Continue reading the main story

“Start Quote

If we look again at them in a few million years, they may have no trace of a circadian rhythm”

Nick Foulkes Karlsruhe Institute of Technology

This is most obvious to us when we travel across time zones, as jet lag is caused by the delay in our circadian rhythm synchronising with the new daylight times.

On a smaller scale, the body clock can be measured by the switching on and off of certain "clock genes" at different times during the day. This happens automatically daily, but is synchronised with the day-night cycle through exposure to light.
Light is detected primarily by the eyes, but most cells in the body have some reaction to light levels. In non-mammalian animals, such as fish, these "peripheral" detectors play a more important role.
This means that, even though the cavefish have lost their eyes over the course of evolution, their bodies should still be able to react to changes in light.
When comparing the reactions of the circadian rhythm of the cavefish to those of a "normal" zebrafish, however, the blind fish showed none of the responses to external light changes that the zebrafish did.
After two million years in the dark, the cavefish have no need to react to the light, and their body clocks have permanently changed to reflect this.
Alternative triggers But these blind fish do still have a body clock, which can be reset by triggers other than light.
Feeding the fish at regular times showed that both the zebrafish and the cavefish responded by resetting their circadian rhythms.
Furthermore, when the cavefish were left to reset their clock according to their natural rhythm, the researchers found that their "day" is 47 hours long.
Professor Foulkes said that this was "possibly linked with food availability, or we could have caught them in the process of losing their clocks. If we look again at them in a few million years, they may have no trace of a circadian rhythm".
The team plans to investigate whether this gradual loss of body clock is a common feature among all species of fish living in perpetual darkness.

25 May 2011 Last updated at 18:12 GMT

Cosmic distance record 'broken'

By Jonathan Amos Science correspondent, BBC News

The blast may have occurred a mere 520 million years after the Big Bang

A cataclysmic explosion of a huge star near the edge of the observable Universe may be the most distant single object yet spied by a telescope.

Scientists believe the blast, which was detected by Nasa's Swift space observatory, occurred a mere 520 million years after the Big Bang.
This means its light has taken a staggering 13.14 billion years to reach Earth.
Details of the discovery will appear shortly in the Astrophysical Journal.
The event, which was picked up by Swift in April 2009, is referred to by astronomers using the designation GRB 090429B.
The "GRB" stands for "gamma-ray burst" - a sudden pulse of very high-energy light that the telescope is tuned to find on the sky.
These bursts are usually associated with extremely violent processes, such as the end-of-life collapse of giant stars.
"It would have been a huge star, perhaps 30 times the mass of our Sun," said lead researcher Dr Antonino Cucchiara from the University of California, Berkeley.
"We do not have enough information to claim this was one of the so-called 'Population III" stars, which are the very first generation of stars in the Universe. But certainly we are in the earliest phases of star formation," he told BBC News.
Swift, as its name implies, has to act quickly to catch gamma-ray flashes because they will register for only a few minutes.
Record breaker Fortunately, an afterglow at longer wavelengths will persist sometimes for days, which allows follow-up observations by other telescopes that can then determine distance.
It was this afterglow analysis that established another burst in the week previous to GRB 090429B to be at a separation from Earth of 13.04 billion light-years, making it temporarily the "most distant object in the Universe".

The event was picked up in April 2009 by Nasa's Swift telescope

This other event (GRB 090423) was reported fairly soon after its occurrence, but it has taken astronomers two years to come back with a confident assessment that an even greater expanse lies between Earth and GRB 090429B.
There are other competing candidates for the title of "most distant object". Hubble, for example, was given much more powerful instruments during its final astronaut servicing mission in 2009, and teams working on new images from the famous space telescope have seen galaxies that look not far short of GRB 090429B - and potentially even further out.
It should be stated, of course, that in these sorts of observations, there is always a degree of uncertainty.
Hubble's targets were galaxies - collections of stars; and GRB 090429B is the signature of a single event, a single star. So, in that sense, it might be considered apart.
Scientists are very keen to probe these great distances because they will learn how the early Universe evolved, and that will help them explain why the cosmos looks the way it does now.
They are particularly keen to trace the very first populations of stars. These hot, blue giants would have grown out of the cold neutral gas that pervaded the young cosmos.
Brilliant but brief These behemoths would have burnt brilliant but brief lives, producing the very first heavy elements.
Their intense ultra-violet light would also have "fried" the neutral gas around them - ripping electrons off atoms - to produce the diffuse intergalactic plasma we still detect between nearby stars today.

A GAMMA-RAY BURST RECIPE

• Models assume GRBs arise when giant stars burn out and collapse
• During collapse, super-fast jets of matter burst out from the stars
• Collisions occur with gas already shed by the dying behemoths
• The interaction generates the energetic signals detected by Swift
• Remnants of the huge stars end their days as black holes

So, apart from its status as a potential record-breaker, GRB 090429B is of intense interest because it is embedded directly in this time period - the "epoch of re-ionisation", as astronomers call it.

Whether GRB 090429B was one of the very first stars to shine in the Universe is doubtful, as Dr Cucchiara states. There may be several generations before it.
But Swift will keep looking, and it is ideally suited for the purpose, explains co-researcher Dr Paul O'Brien from the University of Leicester, UK.
"By finding the most distant objects we get an estimate, of course, of when the first objects formed," he told BBC News. "But then if you can find a location on the sky - in this case of a single star - you can go and look for the galaxy this object is presumably in, and you can start to study the very first galaxies.
"Because gamma-rays can get right through dust, this gives you a good, unbiased way of finding those first galaxies. One could just find very bright galaxies, whereas Swift means we can find the smaller galaxies, too. It was all of these objects that grew up to form the Universe we see around us today. If you think in terms of a human lifespan, it's about understanding what the Universe was like as a toddler."
The Swift mission was launched in 2004. It is a US space agency-managed venture but has a big UK and Italian contribution.
Britain's major input has been to provide an X-ray camera and core elements of the satellite's Ultraviolet/Optical Telescope.

Observations made at longer wavelengths - as in this infrared image of GRB 090429B taken by the Gemini North Telescope - are used to work out the distance

Futurology: The tricky art of knowing what will happen next

By Finlo Rohrer BBC News Magazine

Cheap air travel was among the predictions (illustration from Geoffrey Hoyle's book)

A 1972 book which predicts what life would be like in 2010 has been reprinted after attracting a cult following, but how hard is it to tell the future?

Geoffrey Hoyle is often asked why he predicted everybody would be wearing jumpsuits by 2010. He envisioned a world where everybody worked a three-day week and had their electric cars delivered in tubes of liquid.
These colourful ideas from his 1972 children's book, 2010: Living in the Future, helped prompt a Facebook campaign to track him down. His work has now been reprinted with the year in the title amended to 2011.
"I've been criticised because I said people [would] wear jumpsuits," explains Hoyle, the son of noted astronomer and science fiction author Fred Hoyle. "We don't wear jumpsuits but to a certain extent the idea of the jumpsuit is the restriction of liberties."
Hoyle's book is a product of its time. The move towards a planned society with an emphasis on communal living colour it.

Fortunately, jumpsuit proliferation has not occurred as Hoyle predicted

"Most of it is based on the evolution of a political system," Hoyle notes.
The author also predicted widespread use of "vision phones" and doing your grocery shopping online.
He is one of a long line of science fiction authors to have tried their hand at futurology, the discipline of mapping out the future.
"If you go back over the years in terms of science fiction and fantasy you find many very brilliant simulations of futures that have occurred," says Richard Rhodes, author of Visions of Technology: A Century of Vital Debate about Machines, Systems, and the Human World.
Perhaps one of the most celebrated pieces of futurology by a science fiction author was Arthur C Clarke's prediction of a network of satellites in geostationary orbits [effectively remaining at the same spot in relation to a fixed point back on earth].
The idea of satellites in geostationary orbit had been floated before but Clarke was the first to see the possibilities for their use as relays for broadcasting and communications.
And HG Wells was years ahead of his time, predicting nuclear weapons in 1914, and later inspiring physicist Leo Szilard.

FAMOUS PREDICTIVE HITS

• Arthur C Clarke: Network of geostationary communications satellites
• HG Wells: Nuclear weapons, world wars, rise of air power
• George Orwell: Monitoring of population as standard

In more recent times, author David Brin, in the 1989 novel Earth and in his other works, predicted citizen reporters, personalised web interfaces, and the decline of privacy.

"The top method is simply to stay keenly attuned to trends in the laboratories and research centres around the world, taking note of even things that seem impractical or useless," says Brin.
"You then ask yourself: 'What if they found a way to do that thing ten thousand times as quickly/powerfully/well? What if someone weaponised it? Monopolised it? Or commercialised it, enabling millions of people to do this new thing, routinely? What would society look like, if everybody took this new thing for granted?'"
Conscious efforts at futurology go back a long way. In 1931, to celebrate its 80th anniversary, the New York Times went to several prominent men for their predictions of what life would be like in 2011.
There were "hits". William Mayo predicted a 70-plus-year lifespan. Other predictions about an ageing population and less importance for national boundaries were promising.

HG Wells predicted nuclear weapons 30 years before it became a reality

But there were bad misses - certainly for Michael Pupin, the physicist - who predicted the equitable distribution of wealth.
A similar exercise had been undertaken in 1893 - looking forward to 1993 - for the Columbian Exposition in Chicago. Florida as a major tourist destination and fast trains are among the hits, but there are many misses.
Politician John J Ingalls was one of the most prescient when he wrote about travelling from New York to London in less than a day.
Predictions, failed or successful, tell us as much about the time they were made as they do about the future.
Go back to the early years of the Cold War and predictions of catastrophic nuclear war were widespread.
"It is the dog that didn't bark," says Rhodes, also author of The Twilight of the Bomb. "In the nuclear community in the years after World War II, they were pretty clear if we didn't eliminate nuclear weapons, if they didn't get it under control, there would inevitably be a nuclear war.
"They didn't see the deep existential fear those weapons induced in leaders of the various countries."
And it's easy to get things wrong or to miss a potential development, because an insurmountable obstacle seems to stand in the way.

Internet grocery shopping isn't exactly like this

One common wrong prediction, made by utopian socialists in the 19th Century, and cropping up in 1893 and 1931 and many times since, is the idea that mechanisation just has to go a bit further to earn us all a life of leisure.
Hoyle's three day week for 2010 has failed to materialise. "People are going to have to work very hard. It's gone the other way. People are working seven days a week. I'm very pessimistic now," he says.
But Hoyle got it right when predicting the role of the vision phone. And the vision desk sounds rather familiar too. "The glass on top of the screen is made in a special way so that when you write on it the camera photographs what you write."
If you predicted today that within a few years time key electronic devices like phones, GPS and media players would be embedded in the human body, you would hardly be saying anything daring.
"It's fairly straightforward to extrapolate from existing technology - that tends to be what people do," says Rhodes. "But the really important changes are almost inevitably complete surprises."
The proliferation of the computer and the microchip comes into this category, says Tim Mack, president of the World Future Society.
"Computers were all looked at as big data crunchers," says Mack. "People missed that - the embedding of chips in just about everything."
Futurology is big business now. The defence industry picked it up a long time ago, but now it's used in everything from consumer technology to food firms.
And it will still prove delightful to read 2010's predictions in a century's time.

Swearing can help relieve pain, study claims

Swearing after hurting yourself can help numb the pain of an injury, new research suggests.

Research proves that swearing triggers not only an emotional response, but a physical one too Photo: ALAMY

10:05AM BST 18 Apr 2011

27 Comments

Scientists from Keele University found that letting forth a volley of foul language can have a powerful painkilling effect, especially for people who do not normally use expletives.

To test the theory, student volunteers placed their hands in a bucket of ice cold water while swearing repeatedly.

They then repeated the exercise but, instead of swearing, used a harmless phrase instead.

Researchers found that the students were able to keep their hands submerged in the icy water for longer when repeating the swear word - establishing a link between swearing and an increase in pain tolerance.

They also found that the pain-numbing effect was four times more likely to work in the volunteers who did not normally use bad language.

The team believes the pain-lessening effect occurs because swearing triggers the ''fight or flight'' response.
The accelerated heart rates of the students repeating the swear word may indicate an increase in aggression, in a classic fight or flight response of ''downplaying feebleness in favour of a more pain-tolerant machismo''.
The research proves that swearing triggers not only an emotional response, but a physical one too, which may explain why the centuries-old practice of cursing developed and why it still persists today.
Dr Richard Stephens, who worked on the project, said: ''Swearing has been around for centuries and is an almost universal human linguistic phenomenon.
''It taps into emotional brain centres and appears to arise in the right brain, whereas most language production occurs in the left cerebral hemisphere of the brain.
''Our research shows one potential reason why swearing developed and why it persists.''

'Music of the stars' now louder

By Jason Palmer Science and technology reporter, BBC News, Washington, DC

Kepler studies of distant stars will help us understand our own local star, the Sun, much better

Continue reading the main story

Related Stories

• Distant star makes music
• First stellar 'heartbeat' heard
• Mission guide: Corot

The Kepler space telescope measures the sizes and ages of stars five times better than any other means - when it "listens" to the sounds they make.

Bill Chaplin, speaking at the AAAS conference in Washington, said that Kepler was an exquisite tool for what is called "astroseismology".
The technique measures minuscule variations in a star's brightness that occur as soundwaves bounce within it.
The Kepler team has now measured some 500 far-flung stars using the method.
Bill Chaplin of the University of Birmingham told the annual meeting of the American Association for the Advancement of Science that astroseismology was, in essence, listening to the "music of the stars".
But it is not sound that Kepler measures. Its primary job is spotting exoplanets, by measuring the tiny dip in the amount of light that it sees when a planet passes in front of a distant star.
Such precision light-level measurements also work for astroseismology, because as sound waves resonate within a star, they slightly change both the brightness and the colour of light that is emitted.

Continue reading the main story

“Start Quote

I could literally spend the rest of my research career working on these data”

End Quote Bill Chaplin University of Birmingham

Researchers can deduce the acoustic oscillations that gave rise to the ripples on the light that Kepler sees.

Like a musical instrument, the lower the pitch, the bigger the star. That means that the sounds are thousands of times lower than we can hear.
But there are also overtones - multiples of those low frequencies - just like instruments, and these give an indication of the depth at which the sound waves originate, and the amount of hydrogen or helium they are passing through.
Since stars fuse more and more hydrogen into helium as they grow older, these amounts give astroseismologists a five-fold increase in the precision of their age estimates for stars.
"With conventional astronomy, when we look at stars we're seeing the radiation emitted at their surfaces; we can't actually see what's happening inside."
"Using the resonances, we can literally build up a picture of what the inside of a star looks like - there's no other way of doing that. It's not easy to do, but we're now getting there, thanks to Kepler."
Kepler is not the first mission to lend itself to astroseimology; Canada's Most and Esa's Corot satellites, for example, are designed specifically to collect similar data.
But just the first few months of observations by Kepler has provided scientists with data on hundreds of stars, whereas Dr Chaplin said that only about 20 have been studied in detail before.
"Suddenly we have this huge database to mine," he said.
"I could literally spend the rest of my research career working on these data - we're just starting to mine them."

Page last updated at 05:10 GMT, Tuesday, 2 March 2010

Ice deposits found at Moon's pole

By Paul Rincon Science reporter, BBC News, The Woodlands, Texas

India's Chandrayaan-1 probe carried US equipment to the Moon

A radar experiment aboard India's Chandrayaan-1 lunar spacecraft has identified thick deposits of water-ice near the Moon's north pole.

The US space agency's (Nasa) Mini-Sar experiment found more than 40 small craters containing water-ice.

But other compounds - such as hydrocarbons - are mixed up in lunar ice, according to new results from another Moon mission called LCROSS.

The findings were presented at a major planetary science conference in Texas.

The craters with ice range from 2km to 15km (one to nine miles) in diameter; how much there is depends on its thickness in each crater. But Nasa says the ice must be at least a couple of metres thick to give the signature seen by Chandrayaan-1.

Dr Paul Spudis, from the Lunar and Planetary Institute in Houston, estimated there was at least 600 million metric tonnes of water-ice held within these impact craters.

The equivalent amount, expressed as rocket fuel, would be enough to launch one space shuttle per day for 2,200 years, he told journalists at the 41st Lunar and Planetary Science Conference.

What all these craters have in common are large areas of their interiors that never see sunlight.

Extreme cold

Temperatures in some of these permanently darkened craters can drop as low as 25 Kelvin (-248C; -415F) - colder than the surface of Pluto - allowing water-ice to remain stable.

"It is mostly pure water-ice," said Dr Spudis. "It could be under a few tens of centimetres of dry regolith (lunar soil)."

This protective layer of soil could prevent blocks of pure ice from vaporising even in some areas which are exposed to sunlight, he explained.

Ice thrown up by the LCROSS impact was in a crystalline form

In February, President Barack Obama cancelled the programme designed to return Americans to the Moon by 2020.

However, Dr Spudis said: "Now we can say with a fair degree of confidence that a sustainable human presence on the Moon is possible. It's possible using the resources we find there.

"The results from these missions, that we have seen in the last few months, are totally revolutionising our view of the Moon."

Chandrayaan-1 was India's contribution to the armada of unmanned spacecraft to have been launched to the Moon in recent years. Japan, Europe, China and the US have all sent missions packed with instruments to explore Earth's satellite in unprecedented detail.

In Nasa's LCROSS mission, a rocket and a probe were smashed into a large crater at the lunar south pole, kicking up water-ice and water vapour.

Spectral measurements of material thrown up by the LCROSS impact indicate some of the water-ice was in a crystalline form, rather than the "amorphous" form in which the water molecules are randomly arranged.

Water source

"There's not one flavour of water on the Moon; there's a range of everything from relatively pure ice all the way to adsorbed water," said the mission's chief scientist Anthony Colaprete, from Nasa's Ames Research Center.

"And here is an instance inside Cabeus crater where it appears we threw up a range of fine-grained particulates of near pure crystalline water-ice."

Overall, results from recent missions suggest there could be several sources for lunar ice.

One important way for water to form is through an interaction with the solar wind, the fast-moving stream of particles that constantly billows away from the Sun.

Space radiation triggers a chemical reaction in which oxygen atoms already in the soil acquire hydrogen nuclei to make water molecules and the simpler hydrogen-oxygen (OH) molecule. This "adsorbed" water may be present as fine films coating particles of lunar soil.

In a cold sink effect, water from elsewhere on the lunar surface may migrate to the slightly cooler poles, where it is retained in permanently shadowed craters.

Scientists have also reported the presence of hydrocarbons, such as ethylene, in the LCROSS impact plume. Dr Colaprete said any hydrocarbons were likely to have been delivered to the lunar surface by comets and asteroids - another vital source of lunar water.

However, he added, some of these chemical species could arise through "cold chemistry" on interstellar dust grains accumulated on the Moon.

In addition to water, researchers have seen a range of other "volatiles" (compounds with low boiling points) in the impact plume, including sulphur dioxide (SO2) and carbon dioxide (CO2).

The results from the Mini-Sar instrument are due to be published in the journal Geophysical Research Letters. The team is currently analysing results for craters at the Moon's south pole.

Monkeys 'display self-doubt' like humans

Page last updated at 01:17 GMT, Monday, 21 February 2011

Monkeys 'display self-doubt' like humans

By Victoria Gill Science and nature reporter, BBC News

Macaques 'self-doubt like humans'

Monkeys trained to play computer games have helped to show that it is not just humans that feel self-doubt and uncertainty, a study says.

US-based scientists found that macaques will "pass" rather than risk choosing the wrong answer in a brainteaser task.

Awareness of our own thinking was believed to be a uniquely human trait.

But the study, presented at the AAAS meeting in Washington DC, suggests that our more primitive primate relatives are capable of such self-awareness.

Professor John David Smith, from State University of New York at Buffalo and Michael Beran, from Georgia State University, carried out the study.

These results could help explain why self-awareness is such an important part of our cognitive makeup and from whence it came John David Smith Lead researcher

They trained the macaques, which are Old World monkeys, to use a joystick-based computer game.

The animals were trained to judge the density of a pixel box that appeared at the top of the screen as either sparse or dense. To give their answer, the monkeys simply moved a cursor towards a letter S or a letter D.

When the animals chose the correct letter, they were rewarded with an edible treat. There was no punishment for choosing the wrong answer, but the game briefly paused, taking away - for a few seconds - the opportunity for the animals to win another treat.

But the monkeys had a third option - choosing a question mark - which skipped the trial and moved on to the next one. This meant no treat, but it also meant no pause in the game.

The scientists saw that the macaques used this option in exactly the same way as human participants who reported that they found a trial too tricky to answer; they chose to "pass" and move on.

Dr Smith presented footage of the animals playing the game at a session that was organised by the European Science Foundation.

"Monkeys apparently appreciate when they are likely to make an error," he told BBC News. "They seem to know when they don't know."

In the same trial, capuchins, which belong to the group known as New World monkeys, failed to take this third option.

Dr Smith explained: "There is a big theoretical question at stake here: Did [this type of cognition] develop only once in one line of the primates - emerging only in the line of Old World primates leading to apes and humans?"

He said that the capacity to think in this way was "one of the most important facets of humans' reflective mind, central to every aspect of our comprehension and learning".

"These results... could help explain why self-awareness is such an important part of our cognitive makeup and from whence it came," he added.

Liars' brains 'are not the same'

Last Updated: Thursday, 29 September 2005, 23:40 GMT 00:40 UK

Liars' brains 'are not the same'

A deceitful person's brain is different, the study suggests

Habitual liars' brains differ from those of honest people, a study says.

A University of Southern California team studied 49 people and found those known to be pathological liars had up to 26% more white matter than others.

White matter transmits information and grey matter processes it. Having more white matter in the prefrontal cortex may aid lying, the researchers said,

But the British Journal of Psychiatry said there were likely to be more differences in the brains of liars.

Manipulative behaviour

Participants were volunteers drawn from five temporary employment agencies in Los Angeles.

Three separate groups were studied.

The issue is always how much of our behaviour is under voluntary control and how much is innate Dr Cosmo Hallstrom, Consultant Psychiatrist

The first consisted of 12 men and women with a history of being pathological liars; the second was 21 people who did not have a history of lying or anti-social behaviour.

The third group consisted of 16 people with anti-social personality disorder but no history of pathological lying. They were studied to see if they showed the same brain make-up as liars.

The researchers drew up a list of criteria for lying, cheating and deceiving, including habits such as conning people or behaving manipulatively, and telling lies in order to obtain sickness benefits.

They also assessed how much grey and white matter people had in the prefrontal cortex areas of their brains, using structural magnetic resonance imaging (MRI).

Liars were found to have between 22 and 26% more white matter than either those with no history of lying or those in the anti-social group.

Childhood

The findings could not be explained by differences in age, ethnicity, IQ, head injury or substance misuse.

This is the first study to show a brain difference in people who lie, cheat and manipulate others, the researchers said.

They said the study could help research into areas such as people who feign illness.

The findings are in line with previous studies which showed children with autism are less capable of lying than other children.

Brain neurodevelopmental studies of autism show people with the condition have more grey matter than white matter - the opposite pattern to the liars in this study.

The researchers say the link between white matter and a deceitful personality could be that white matter provides a person with the cognitive capacity to lie.

Writing in the British Journal of Psychiatry, the research team led by Dr Yaling Yang, say: "To our knowledge, this is the first study to show a brain abnormality in people who lie, cheat and manipulate others.

"The results further implicate the prefrontal cortex as an important - but not sole - component in the neural circuitry underlying lying, and provide an initial neurological correlate of a deceitful personality."

They add: "Further studies are required to examine changes in brain anatomy during the critical neurodevelopmental period in childhood, alongside changes in lying ability, to test further our preliminary hypothesis on the link between prefrontal white matter and lying."

Dr Cosmo Hallstrom, a consultant psychiatrist in London, said: "The issue is always how much of our behaviour is under voluntary control and how much is innate.

"The finding of brain abnormalities lends weight to the idea that a strong component of such difficulties may well be beyond voluntary control at least in part."

17 September 2010 Last updated at 09:52 GMT

It's good to think - but not too much, scientists say

By Katie Alcock Science reporter, BBC News

People who think more about their decisions have more brain cells in their frontal lobes

People who think more about whether they are right have more cells in an area of the brain known as the frontal lobes.

UK scientists, writing in Science, looked at how brain size varied depending on how much people thought about decisions.

But a nationwide survey recently found that some people think too much about life.

These people have poorer memories, and they may also be depressed.

Stephen Fleming, a member of the University College London (UCL) team that carried out the research, said: "Imagine you're on a game show such as 'Who Wants to Be a Millionaire' and you're uncertain of your answer. You can use that knowledge to ask the audience, ask for help."

The London group asked 32 volunteers to make difficult decisions. They had to look at two very similar black and grey pictures and say which one had a lighter spot.

They then had to say just how sure they were of their answer, on a scale of one to six. Although it was hard to tell the difference, the pictures were adjusted to make sure that no-one found the task harder than anyone else.

People who were more sure of their answer had more brain cells in the front-most part of the brain - known as the anterior prefrontal cortex.

This part of the brain has been linked to many brain and mental disorders, including autism. Previous studies have looked at how this area functions while people make real time decisions, but not at differences between individuals.

Illness link

The study is the first to show that there are physical differences between people with regard to how big this area is. These size differences relate to how much they think about their own decisions.

The researchers hope that learning more about these types of differences between people may help those with mental illness.

Co-author Dr Rimona Weil, from UCL's Institute of Cognitive Neuroscience, said: "I think it has very important implications for patients with mental ill health who perhaps don't have as much insight into their own disease."

She added that they hope they may be able to improve patients' ability to recognise that they have an illness and to remember to take their medication.

However, thinking a lot about your own thoughts may not be all good.

Cognitive psychologist Dr Tracy Alloway from the University of Stirling, who was not involved in the latest study, said that some people have a tendency to brood too much and this leads to a risk of depression.

More than 1,000 people took part in a nationwide study linking one type of memory - called "working memory" - to mental health.

Working memory involves the ability to remember pieces of information for a short time, but also while you are remembering them, to do something with them.

For example, you might have to keep hold of information about where you saw shapes and colours - and also answer questions on what they looked like. Dr Alloway commented: "I like to describe it as your brain's Post-It note."

Those with poorer working memory, the 10-15% of people who could only remember about two things, were more likely to mull over things and brood too much.

Both groups presented their findings at the British Science Festival, held this year at the University of Aston in Birmingham.

Computers show how wind could have parted Red Sea

Computer simulations show how the movement of wind could have parted the waters of the Red Sea

New computer simulations have shown how the parting of the Red Sea, as described in the Bible, could have been a phenomenon caused by strong winds.

The account in the Book of Exodus describes how the waters of the sea parted, allowing the Israelites to flee their Egyptian pursuers.

Simulations by US scientists show how the movement of wind could have opened up a land bridge at one location.

This would have enabled people to walk across exposed mud flats to safety.

The results are published in the open-access journal Plos One.

The researchers show that a strong east wind, blowing overnight, could have pushed water back at a bend where an ancient river is believed to have merged with a coastal lagoon.

63mph winds from the east could have pushed the water back at an ancient river bend

With the water pushed back into both waterways, a land bridge would have opened at the bend, enabling people to walk across exposed mud flats to safety.

As soon as the wind died down, the waters would have rushed back in.

The study is based on a reconstruction of the likely locations and depths of Nile delta waterways, which have shifted considerably over time.

"The simulations match fairly closely with the account in Exodus," said the study's lead author Carl Drews, from the US National Center for Atmospheric Research (NCAR).

"The parting of the waters can be understood through fluid dynamics. The wind moves the water in a way that's in accordance with physical laws, creating a safe passage with water on two sides and then abruptly allowing the water to rush back in."

The study is part of a larger research project by Mr Drews into the impacts of winds on water depths, including the extent to which Pacific Ocean typhoons can drive storm surges.

By pin-pointing a possible site south of the Mediterranean Sea for the crossing, the study also could be of benefit to archaeologists seeking to research the account.

A way through

In the Book of Exodus, Moses and the fleeing Israelites became trapped between the Pharaoh's advancing chariots and a body of water that has been variously translated as the Red Sea or the Sea of Reeds.

The Biblical account says that, as the Pharaoh's army followed, the waters rushed in

In a divine miracle, the account says, a mighty east wind blew all night, splitting the waters and leaving a passage of dry land with walls of water on both sides.

The Israelites were able to flee to the other shore. But when the Egyptian Pharaoh's army attempted to pursue them in the morning, the waters rushed back and drowned the soldiers.

Other scientists have also sought to explain the account through natural processes.

Some have speculated that a tsunami could have caused waters to retreat and advance rapidly. But the scientists behind the latest research point out that such an event would not have caused the gradual overnight divide of the waters or have been associated with winds.

Other researchers have focused on a phenomenon known as "wind setdown," in which a particularly strong and persistent wind can lower water levels in one area while piling up water downwind.

28 September 2010 Last updated at 23:55 GMT

Not depressed, just sad, lonely or unhappy

Is sad so bad?

Cases of depression have grown around the world. But while awareness of the illness has helped lift the stigma it once attracted, have we lost touch with the importance of just feeling sad, asks Mary Kenny.

Continue reading the main story

In today's Magazine

• How long will miners' euphoria last?
• Do foreigners love Britain for being fair?
• What's an egg got to do with inventing?
• Are the pips squeaking yet?

Looking back on my own reasonably serene childhood in Ireland during the 1950s, I recall quiet murmurs about people who suffered from "nerves".

I remember hearing that a neighbour - a well-to-do woman whose larger house and smart appearance was rather envied in the community - had had a "nervous breakdown".

Although when I repeated this to my aunt and uncle, with whom I was living, I was hushed up with a peremptory word of censure. There was, clearly, something slightly shameful about a "nervous breakdown" and one didn't speak about it.

I can see now, though I did not see then, that these were hidden incidents of depression among family and neighbours. But the stigma over depression, or even mental illness of any kind, must have added to their anguish.

How times have changed. It is an accepted truth, in our time, that depression is an illness with a global reach.

Continue reading the main story

“Start Quote

We are losing old rituals which human beings have practised for eons”

End Quote Mary Kenny

It seems that depression in various guises - whether chronic, uni-polar, bi-polar, clinical, recurrent, major or minor - accounts for a greater burden of disease, world-wide, than war, cancer and AIDS all put together.

This new openness is a good thing. Yet in the process, are we losing something?

Take the word, "trauma," which is now frequently and commonly invoked in conversation today. A person who has suffered a bereavement is said to be "in trauma".

A person who has been subjected to shock is said to be "traumatised". The break-up of relationships - a sad human experience which brings us a sense of loss, and hurts our need for attachment - is, similarly, described as "a traumatic experience".

In his excellent autobiographical study of depression which he so adroitly called Malignant Sadness, Professor Lewis Wolpert employs the concept of "trauma" to describe, for example, bereavement.

Death - part of life

"Trauma" comes from the Greek word for a "wound", and in a medical sense, it is what happens to the body when a wound delivers a shock.

Continue reading the main story

Find out more

Mary Kenny's Medicalising Melancholy is on BBC Radio 4 on Wednesday 29 Sept at 2045 BST

• Or listen to it later on the iPlayer
• Headroom: Emotional health

But bereavement, of which I have much sorrowful experience is, alas, part of the natural course of life's sad events.

As Shakespeare observes, with Hamlet, his father lost a father, and that father lost a father before him, and so on, ad infinitum, through the hinterland of human history.

Grief is desperately upsetting: it hurts you for ages, and the loss of someone you love is emotionally painful, and can be enduringly so. But why not call it by its proper name: bereavement: grief: loss?

One reason may be that we are losing old rituals which human beings have practised for eons.

When I was a young woman in France in the 1960s, you would come across a shop with its blinds drawn, and a notice saying: "Ferme pour deuil": closed for mourning.

Virginia Woolf endured a condition of fatigue, loss of motivation and energy

It is still seen in France, and is also a usual response in Italy. Mourning symbols were widespread in all cultures - widows' weeds, black armbands - and the community was expected to respect those who mourn.

Outward signs of mourning have declined, if not been abolished in more secular societies now: but our sense of sadness and loss endure, and instead of this being called mourning, it is called "trauma".

It might be a start to revive or recapture some of the wider, non-medical vocabulary for the gamut of human experience.

Depression may also be melancholy: it may be discouragement, disappointment, abandonment, sadness, sorrow, mourning, rejection, regret, anxiety, grief, obsession, introspection, loss, separation, loneliness, isolation, alienation, guilt, loss of hope, temperamental woe and simple, pure, unhappiness.

It can be forms of low mood now out of date. The Edwardians were very keen on a condition known as "neurasthenia"; Virginia Woolf was diagnosed with it.

It was also known as "nervous debility", or, in its milder form, being hyper-sensitive and thin-skinned.

Yearning for the past

"Anomie" was another condition once favoured in the 19th Century by the sociologist Emile Durkheim, and from a sociologist, a sociological condition. Anomie was defined as an isolated mood caused by the breakdown of social norms, sense of purpose and rules of conduct.

Continue reading the main story

“Start Quote

There are romantic-sounding forms of melancholy: the German idea of weltschmerz - a yearning sense of 'world-sorrow'”

End Quote

There was also a spiritual form of depression called "accidie" much brooded on by some of the saints - this was "dryness of the soul". The writer Malcolm Muggeridge also complained of suffering from it at times.

There are even, I think, some romantic-sounding forms of melancholy: the German idea of weltschmerz - a yearning sense of "world-sorrow" and unfocused sadness for humanity: or the French nostalgie du passé, that bittersweet Proustian condition of longing for the past, with a rueful sense of regret for missed chances and lost opportunities.

I also rather like mal du pays - the exile's yearning for the country of childhood, and it comes to me in flashes, both in the spring and autumn, when I think of Irish country lanes, and the smell of fields of mown hay. Ah, bonjour tristesse!

No doubt we are better off for shedding much of the stigma surrounding mental illness - but with it, have we lost some of the variety, the dark poetry of the human condition?

Mary Kenny is an author, journalist and public speaker

14 October 2010 Last updated at 07:57 GMT

Background noise affects taste of foods, research shows

By Jason Palmer Science and technology reporter, BBC News

This might be the best place for the tastiest meal

The level of background noise affects both the intensity of flavour and the perceived crunchiness of foods, researchers have found.

Blindfolded diners assessed the sweetness, saltiness, and crunchiness, as well as overall flavour, of foods as they were played white noise.

While louder noise reduced the reported sweetness or saltiness, it increased the measure of crunch.

The research is reported in the journal Food Quality and Preference.

It may go some way to explaining why airline food is notoriously bland - a phenomenon that drives airline catering companies to heavily season their foods.

"There's a general opinion that aeroplane foods aren't fantastic," said Andy Woods, a researcher from Unilever's laboratories and the University of Manchester.

"I'm sure airlines do their best - and given that, we wondered if there are other reasons why the food would not be so good. One thought was perhaps the background noise has some impact," he told BBC News.

"Nasa gives their space explorers very strong-tasting foods, because for some reason thay can't taste food that strongly - again, perhaps it's the background noise.

"There was no previous research on this, so we went about seeing if the hunch was correct."

Tasteful

In a comparatively small study, 48 participants were fed sweet foods such as biscuits or salty ones such as crisps, while listening to silence or noise through headphones.

Meanwhile they rated the intensity of the flavours and of their liking.

In noisier settings, foods were rated less salty or sweet than they were in the absence of background noise, but were rated to be more crunchy.

"The evidence points to this effect being down to where your attention lies - if the background noise is loud it might draw your attention to that, away from the food," Dr Woods said.

Also in the group's findings there is the suggestion that the overall satisfaction with the food aligned with the degree to which diners liked what they were hearing - a finding the researchers are pursuing in further experiments.

NHS money 'wasted' on homeopathy

Page last updated at 14:41 GMT, Monday, 22 February 2010

The NHS should stop funding homeopathy, MPs say.

The House of Commons Science and Technology Committee said using public money on the highly-diluted remedies could not be justified.

The cross-party group said there was no evidence beyond a placebo effect, when a patient gets better because of their belief that the treatment works.

But manufacturers and supporters of homeopathy disputed the report, saying the MPs had ignored important evidence.

It is thought about £4m a year is spent on homeopathy by the NHS, helping to fund four homeopathic hospitals in London, Bristol, Liverpool and Glasgow and numerous prescriptions.

Homeopathy is a 200-year-old system of treatment that uses highly diluted substances - sometimes so none of the original product is left - that are given orally in the belief that it will stimulate the body's self-healing mechanism.

HOMEOPATHY Homeopathy involves giving people very dilute amounts of a substance that in larger amounts might produce symptoms similar to the condition being treated For example, one remedy which might be used in a person suffering from insomnia is coffea, a remedy made from coffee Homeopathy: Your views

Supporters believe the remedies help relieve a range of minor ailments from bruising and swelling to constipation and insomnia.

But the MPs said homeopathy was basically sugar pills that only worked because of faith.

In medicine it is recognised that some people will get better because they believe the treatment they take is going to work.

The MPs said the NHS should not fund treatments on this basis.

They argued the effectiveness was often unpredictable and involved a deception by the medical establishment.

They also warned it could lead to a delay in diagnosis if symptoms were cured but the underlying reason for them was not tackled.

The MPs also criticised the drugs regulator, the Medicines and Healthcare products Regulatory Agency, for allowing medical claims to be made.

The bar for licensing for homeopathic remedies is not set as high as for medical treatments, partly because they have been used since the NHS was set up in 1948 before the current system of regulation was brought in.

Committee chairman Phil Willis said this approval and the fact they were funded by the NHS in the first place lent the remedies "a badge of authority that is unjustified".

But the report acknowledged there was a public appetite for homeopathy with surveys showing satisfaction rates of above 70%.

But the report was disowned by one of the committee's MPs. Labour's Ian Stewart said he was dissenting from the report because the MPs had refused to take into account that homeopathy worked for some people and he also said he was concerned by the "balance of witnesses".

'Disappointed'

Paul Bennett, superintendent pharmacist at Boots, on homeopathy

A spokeswoman for the Department of Health said the government would give a full response to the report in the coming months.

But she added: "In the meantime we would reiterate that we appreciate the strength of feeling both for and against the provision of homeopathy on the NHS.

"Our view is that the local NHS and clinicians, rather than Whitehall, are best placed to make decisions on what treatment is appropriate for their patients - this includes complementary or alternative treatments such as homeopathy."

Robert Wilson, of the British Association of Homeopathic Manufacturers, said he was "disappointed" by the findings.

He said the MPs had ignored evidence that homeopathy was effective.

"There is good evidence that homeopathy works, for example in animals and babies, neither of which experience placebo effects."

And Dr Michael Dixon, medical director for the Prince's Foundation for Integrated Health, set up by Prince Charles to promote complementary medicine, disputed the findings, saying homeopathy still had a role in the NHS.

"We should not abandon patients we cannot help with conventional scientific medicine.

"If homeopathy is getting results for those patients, then of course we should continue to use it."

The British Medical Association said it was concerned about NHS funds being used on homeopathy and called for an official review into its effectiveness.

Happy moments 'protect the heart'

Last Updated: Monday, 18 April, 2005, 15:20 GMT 16:20 UK

Happy moments 'protect the heart'

Happiness was more commonly linked to leisure, rather than work

Every moment of happiness counts when it comes to protecting your heart, researchers have said.

A team from University College London said happiness leads to lower levels of stress-inducing chemicals.

They found that even when happier people experienced stress, they had low levels of a chemical which increases the risk of heart disease.

The research is published in Proceedings of the National Academy of Sciences.

This shows that people who are happy and unstressed are likely to have less potentially dangerous stress chemicals in their bodies Professor Peter Weissberg, British Heart Foundation

It showed that those who were happy less often had higher levels of a bloodstream chemical called plasma fibrinogen, which shows if there is inflammation present.

It is an indicator of how great a risk a person has of developing heart disease in the future.

Daily happiness

Researchers tested 116 men and 100 women who were taking part in a major study of thousands of London-based civil servants recruited between 1985 and 1988 when 35-55 years old to investigate the risk factors for coronary heart disease.

They carried out tests on people at work, during leisure periods and in the laboratory.

People were also asked whether or not they were happy at 33 moments during the day.

The researchers then evaluated how often people were happy in the course of the day.

Leisure was, unsurprisingly, linked with more happy moments than work.

It was found that some people reported they never felt happy, while others reported feeling occasional happiness and those who felt happy most of the time.

The results were adjusted for gender, age, employment status, weight, smoking habits and psychological distress.

Levels of cortisol - a stress hormone - were 32% lower in people who reported more happy moments.

Cortisol has been related to abdominal obesity, Type 2 diabetes, high blood pressure and autoimmune disorders.

The researchers also discovered happy people have had lower levels of fibrinogen when they were stressed.

Emotional state

Professor Jane Wardle, who worked on the study, said: "All the research to date has been on unhappiness, rather than happiness.

"This research suggests we should aim to maximise the happiness of the population."

Professor Andrew Steptoe, who led the study, said: "It has been suspected for the last few years that happier people may be healthier both mentally and physically than less happy people.

"What this study shows is that there are plausible biological pathways linking happiness with health."

He added: "What we find particularly interesting is that the associations between happiness and biological responses were independent of psychological distress.

"We already know that depression and anxiety are related to increased physical health risk. This study raises the intriguing possibility that the effect of happiness may be somewhat separate."

Professor Peter Weissberg, Medical Director at the British Heart Foundation said: "The results of this study build upon this team's work, which we are delighted to have supported.

"Evidence that emotional state is important for good heart health is growing and this shows that people who are happy and unstressed are likely to have less potentially dangerous stress chemicals in their bodies."

Page last updated at 11:30 GMT, Tuesday, 2 March 2010

Did the discovery of cooking make us human?

By Clare Kingston BBC Horizon

Learning to cook created 'big brains'

Cooking is something we all take for granted but a new theory suggests that if we had not learned to cook food, not only would we still look like chimps but, like them, we would also be compelled to spend most of the day chewing.

Without cooking, an average person would have to eat around five kilos of raw food to get enough calories to survive.

The daily mountain of fruit and vegetables would mean a six-hour chewing marathon.

It is already accepted that the introduction of meat into our ancestors' diet caused their brains to grow and their intelligence to increase.

Meat - a more concentrated form of energy - not only meant bigger brains for our ancestors, but also an end to the need to devote nearly all their time to foraging to maintain energy levels.

As a consequence, more time was available for social structure to develop.

'Accident'

Harvard Professor Richard Wrangham believes there is more to it than simply discovering meat.

Australopithecus was ape-like but walked upright like humans

He thinks that it is not so much a change in the ingredients of our diet, but the way in which we prepare them that has caused the radical evolution of our species.

"I think cooking is arguably the biggest increase in the quality of the diet in the whole of the history of life," he says.

"Our ancestors most probably dropped food in fire accidently. They would have found it was delicious and that set us off on a whole new direction."

To understand how and when our bodies changed, we need to take a closer look at what our ancestors ate by studying the fossil records.

Our earliest ancestor was the ape-like Australopithecus.

Australopithecus had a large belly containing a big large-intestine, essential to digest the robust plant matter, and had large, flat teeth which it used for grinding and crushing tough vegetation.

None the less, it was Australopithecus that moved out of the trees and onto the African savannah, and started to eat the animals that grazed there.

And it was this change of habitat, lifestyle and diet that also prompted major changes in anatomy.

Bigger brain

The eating of meat ties in with an evolutionary shift 2.3 million years ago resulting in a more human-looking ancestor with sharper teeth and a 30% bigger brain, called Homo habilis.

The brain consumes 20% of a person's energy while sitting

The most momentous shift however, happened 1.8 million years ago when Homo erectus - our first "truly human" ancestor arrived on the scene.

Homo erectus had an even bigger brain, smaller jaws and teeth.

Erectus also had a similar body shape to us. Shorter arms and longer legs appeared, and gone was the large vegetable-processing gut, meaning that Erectus could not only walk upright, but could also run.

He was cleverer and faster, and - according to Professor Wrangham - he had learned how to cook.

"Cooking made our guts smaller," he says. "Once we cooked our food, we didn't need big guts.

"They're costly in terms of energy. Individuals that were born with small guts were able to save energy, have more babies and survive better."

Professor Peter Wheeler from Liverpool John Moores University and his colleague, Leslie Aiello, think it was this change in our digestive system that specifically allowed our brains to get larger.

Energy transfer

Cooking food breaks down its cells, meaning that our stomachs need to do less work to liberate the nutrients our bodies need.

This, says Wheeler, "freed up energy which could then be used to power a larger brain. The increase in brain-size mirrors the reduction in the size of the gut."

Significantly Wheeler and Aiello found that the reduction in the size of our digestive system was exactly the same amount that our brains grew by - 20%.

Professor Stephen Secor at the University of Alabama found that not only does cooked food release more energy, but the body uses less energy in digesting it.

He uses pythons as a model for digestion as they stay still for up to six days while digesting a meal. This makes them the perfect model as the only energy they expend is on digestion.

His research shows that pythons use 24% less energy digesting cooked meat, compared with raw.

So being human might all be down to energy.

Cooking is essentially a form of pre-digestion, which has transferred energy use from our guts to our brains.

According to Professors Wheeler and Wrangham and their colleagues, it is no coincidence that humans - the cleverest species on earth - are also the only species that cooks.

Page last updated at 23:49 GMT, Thursday, 4 March 2010

Dinosaur extinction link to crater confirmed

By Paul Rincon Science reporter, BBC News, The Woodlands, Texas

The dinosaurs were one of many groups to go extinct

An international panel of experts has strongly endorsed evidence that a space impact was behind the mass extinction event that killed off the dinosaurs.

They reached the consensus after conducting the most wide-ranging analysis yet of the evidence.

Writing in Science journal, they rule out alternative theories such as large-scale volcanism.

The analysis has been discussed at the 41st Lunar and Planetary Science Conference (LPSC) in the US.

A panel of 41 international experts reviewed 20 years' worth of research to determine the cause of the Cretaceous-Tertiary (K-T) mass extinction, around 65 million years ago.

The extinction wiped out more than half of all species on the planet, including the dinosaurs, bird-like pterosaurs and large marine reptiles, clearing the way for mammals to become the dominant species on Earth.

FROM THE TODAY PROGRAMME More from Today programme

Their review of the evidence shows that the extinction was caused by a massive asteroid or comet smashing into Earth at Chicxulub on Mexico's Yucatan Peninsula.

When the 10km-15km space rock struck the Yucatan, the explosive energy released was equivalent to 100 trillion tonnes of TNT - over a billion times more explosive than the bombs dropped on Hiroshima and Nagasaki.

The huge crater that remains from the event is some 180km in diameter and surrounded by a circular fault about 240km in diameter.

"You can actually trace debris right up to the rim of the crater from across the world," Co-author Dr David Kring, from the Lunar and Planetary Institute in Houston, told BBC News.

"You can start in Europe, cross the Atlantic and it just thickens as you approach the Chicxulub impact crater."

Advertisement

BBC's David Shukman: Asteroid was '20 times faster than a bullet'

In the new study, scientists examined the work of palaeontologists, geochemists, climate modellers, geophysicists and sedimentologists who have been gathering evidence about the K-T extinction.

They conclude that the Chicxulub space impact is the only plausible explanation for the devastation evident in geological records.

The initial impact would have triggered large-scale fires, huge earthquakes, and continental landslides which generated tsunamis.

Dr Gareth Collins, one of the review's co-authors from Imperial College London, said the asteroid hit Earth "20 times faster than a speeding bullet".

He added: "The explosion of hot rock and gas would have looked like a huge ball of fire on the horizon, grilling any living creature in the immediate vicinity that couldn't find shelter."

Dr Joanna Morgan, another co-author from Imperial, commented: "The final nail in the coffin for the dinosaurs happened when blasted material was ejected at high velocity into the atmosphere. This shrouded the planet in darkness and caused a global winter, killing off many species that couldn't adapt to this hellish environment."

The ejected debris (white) can be seen in rocks from 65 million years ago

The review confirms that a unique layer of debris ejected from a crater is compositionally linked to the Mexican crater and is also coincident with rocks associated at the Cretaceous-Tertiary (K-T) boundary.

The team also says that an abundance of shocked quartz in rock layers across the world at the K-T boundary lends further weight to conclusions that a massive meteorite impact happened at the time of the mass extinction. This form of the mineral occurs when rocks have been hit very quickly by a massive force. It is only found at nuclear explosion sites and at asteroid impact sites.

"Combining all available data from different science disciplines led us to conclude that a large asteroid impact 65 million years ago in modern day Mexico was the major cause of the mass extinctions," said author Dr Peter Schulte, assistant professor at the University of Erlangen in Germany.

David Kring explained: "I have been invited to give colloquia at a number of universities across North America and I had always been surprised by the number of people who didn't think the connection was as firm as it was.

"I think it was very important for this distinguished panel of experts from around the world who have seen the evidence from their own geographic quarter to debate the issue and come to a final resolution. I think it is that international consensus that is so important in this case."

Today, the crater is buried under Mexico's Yucatan Peninsula, but weaknesses in the overlying rock have produced a ring of slumping that is visible from space

Scientists have previously argued about whether the extinction was caused by a space impact or by volcanic activity in the Deccan Traps in India, where there were a series of super-volcanic eruptions that lasted approximately 1.5 million years.

These eruptions spewed more than 1,000,000 cu km of basaltic lava across the Deccan Traps - enough to fill the Black Sea twice. These were thought to have caused a cooling of the atmosphere and acid rain on a global scale.

Despite evidence for relatively active volcanism in the Deccan Traps at the time, marine and land ecosystems showed only minor changes within the 500,000 years before the time of the K-T mass extinction.

Furthermore, computer models and observational data suggest the release of gases such as sulphur into the atmosphere after each volcanic eruption in the Deccan Traps would have had a short-lived effect on the planet.

The panel also discounted previous studies that suggested the Chicxulub impact occurred 300,000 years prior to the mass extinction event.

Scientists estimate that this type of impact occurs on average about once every 100 million years; about five have occurred during the evolution of complex life on Earth.

The importance of Chicxulub was cemented by the announcement in 1991 of the discovery of shocked quartz in a 1.6km-deep drill hole from the crater.

David Kring, Alan Hildebrand and William Boynton presented their results at that year's LPSC, then held at Nasa's Johnson Space Center in Houston.

Dr Kring explained that he was "elated" with the consensus about the link between Chicxulub and the K-T mass extinction.