In this moving film Horizon follows the Loughran family in their fight to save the life of their daughter Sheila who suffers from cystic fibrosis. They lost their youngest daughter Ann to the disease in 1974 at the age of 15, and now as the health of their third daughter Sheila deteriorates, they must face the prospect of losing a second child. The current shortage of donor organs means that Sheila's only hope of survival is a rare and controversial operation that requires her two surviving siblings to undergo an arduous and potentially fatal operation.

An X-ray of Shelia's lungs Cystic fibrosis (CF) is the most common genetic disease in this country and it is incurable. The lungs of people with cystic fibrosis become covered with a sticky mucus making them extremely susceptible to bacterial infection. Over time these infections badly scar the lungs, until eventually they stop functioning. The defective CF gene is harmless when only a single copy of the gene is inherited. However, both the Loughran parents carry the gene, giving any child they may have a 25% chance of being born with cystic fibrosis. In fact two of their four children were born with the condition.

Horizon joins the family at a time when Sheila's health has deteriorated to such an extent that she requires oxygen 24 hours a day and has only months to live. Although on the waiting list for a donor lung, with 50% of patients dying while waiting to receive a transplant, Sheila's chances are not good.

The family has become aware of a controversial new operation, pioneered in the UK by Professor Sir Magdi Yacoub at Harefield Hospital. The technique, known as Living Donor Lung Transplantation, would involve removing Sheila's diseased lungs and, in an extraordinary three-way operation, replacing them with a lobe from one of the lungs of each her two siblings.

There have been six of these groundbreaking operations carried out in this country. However, only three patients have lived longer than a month. There is a clear moral dilemma - with such a low success rate, is it ethical to put the lives of two healthy people at risk? Even if the operation is initially successful it may only give Sheila five more years to live, by which time her new lungs are likely to fail again.

Damian Loughran Sheila's brother and sister, Damian and Josephine, feel compelled to do anything they can to save their dying sister. They undergo stringent tests before being certain that they are compatible donors and fit for surgery. They will have to face the risk of haemorrhaging and infection, both of which could potentially be fatal. After the operation both donors will be left with a 20-25% permanent loss of lung function. Despite these dangers, Damian and Josephine remain determined to proceed.

As all three of their children are wheeled in for the 12-hour operation, Mary and Harry Loughran's emotion is apparent. A day later, Sheila is breathing with her new lungs, but it is not long before complications arise. She is unable to absorb food and develops an abscess on her lung. Sheila is kept under sedation and so is unaware of these complications. Sadly, three weeks after the operation, Sheila loses her fight for life.

On a barren desert in South America lies one of the greatest archaeological puzzles in the world. Etched in the surface of the desert pampa sand are hundreds of straight lines, geometric shapes and pictures of animals and birds - and their patterns are only clearly visible from the air. They were built by a people called the Nasca - but why and how they created these wonders of the world has defied explanation.

On the pampa, south of the Nasca Lines, archaeologists have now uncovered the lost city of the line-builders, Cahuachi. It was built nearly two thousand years ago and was mysteriously abandoned 500 years later. New discoveries at Cahuachi are at last beginning to give us insight into the Nasca people and to unravel the mystery of the Nasca Lines.

Distorted heads The Lines were first spotted when commercial airlines began flying across the Peruvian desert in the 1920's. Passengers reported seeing 'primitive landing strips' on the ground below. No one knew who had built them or indeed why. Since their discovery, the Nasca Lines have inspired fantastic explanations.

SpiderPerhaps most famously, the Austrian writer Erich von Danikken claimed that they were evidence that the earth had been visited by extra-terrestrials. The lines, he said, were runways for their spacecraft. Scientific study began in the 1940s with the arrival of a German mathematician and astronomer called Maria Reiche. She lived at Nazca until her death in 1998 and was known as the Lady of the Lines. Reiche believed that the lines were a sophisticated astronomical calendar. However, in 1965, astronomer Gerald Hawkins came to Nazca and used computers to check Reiche's theory. Hawkins could find no correlation between the lines and the stars.

Giuseppe Orefici Italian archaeologist Giuseppe Orefici has been excavating the immense Cahuachi site for the last 17 years. Every year he brings a team of specialists to South America for three, intensive months of excavation. Horizon joined Orefici and his team in the hot, windy months of 1998 and this is a fascinating record of their extraordinary finds.

Woven clothCahuachi is emerging as a treasure trove of the Nasca culture. As Orefici and his team excavate, discoveries of paintings on preserved pottery, and the ancient technique of weaving that the Nasca people developed, have given an insight into how the lines may have been made, and what they might have been used for, more than 1500 years ago.

MummyMost exciting is the discovery of human remains. Stunningly preserved in the dry soil of the Peruvian desert are the mummified bodies of the Nasca themselves. Orefici's colleagues Brian Harrison and Andrea Drusini carry out modern autopsies on these remarkable finds, and reveal the strange world and rituals of the Nasca people.

CahuachiOriginally believed to have been a military stronghold, Cahuachi is now reckoned to be a place of ritual and ceremony, and Orefici's stunning new evidence confirms this idea. Cahuachi is now revealed to have been abandoned after a series of natural disasters destroyed the city. But before they left it, the Nasca people covered the city in the arid pampa sand where, until recently, it has remained a barely visible mound in the desert.

There is something so special about diamonds, and they are so valuable, that people have always been prepared to go to the most extraordinary lengths to find them. But how would we feel about the uniqueness of diamonds if it was possible to make one in a laboratory, just like the real thing, down to the nearest atom? In the last few years there has been a scientific race to do exactly this: to manufacture the perfect gem diamond.

Today the dream is close to becoming reality. Science has finally found a way to replicate in a few days something that nature has taken millions of years to produce - diamonds. These man-made diamonds are so close to the real thing, that they have the same atomic structure as natural diamonds. Even the most sophisticated machines are finding it hard to tell the difference. More importantly, these diamonds can be made and sold at a profit.

Synthetic diamond press: This is the story of the race to produce man-made gem diamonds, from the first faltering steps 50 years ago, to today's 'New Alchemists' in Russia who are using the latest science and technology to produce perfect synthetic diamonds in an array of colours and sizes. And it is the story of how this leap in diamond-making technology has forced De Beers to develop ever-more sophisticated detection equipment, trying to spot the synthetics, while the physical distinction between real and man-made diamonds becomes more and more blurred.

Today there are alarm bells ringing at De Beers in Johannesburg. De Beers controls the world diamond trade. By buying up most of the world's uncut diamonds, the company can regulate supply to select dealers, increasing it in good years and reducing it in bad, to keep prices high. Every year 3 billion pounds worth of rough diamonds are distributed around the world for cutting and polishing.

The diamond market survives on public confidence. Already De Beers spends a fortune trying to detect synthetic gems, and teach wholesalers and graders what the molecular differences are. But imagine if these synthetics had exactly the same properties as real diamonds, each atom in place, every manufacturing flaw removed, leaving something indistinguishable from the real thing. They would be undetectable. What would a real diamond be then? To many, the difference would be purely psychological. And so what would happen to public confidence in the natural diamond market?

Man made diamonds: According to the new alchemists, this is all just about to happen.

Hidden deep beneath the Earth's surface lie one of the most destructive and yet least-understood natural phenomena in the world - supervolcanoes. Only a handful exist in the world but when one erupts it will be unlike any volcano we have ever witnessed. The explosion will be heard around the world. The sky will darken, black rain will fall, and the Earth will be plunged into the equivalent of a nuclear winter.

Normal volcanoes are formed by a column of magma - molten rock - rising from deep within the Earth, erupting on the surface, and hardening in layers down the sides. This forms the familiar cone shaped mountain we associate with volcanoes. Supervolcanoes, however, begin life when magma rises from the mantle to create a boiling reservoir in the Earth's crust. This chamber increases to an enormous size, building up colossal pressure until it finally erupts.

The last supervolcano to erupt was Toba 74,000 years ago in Sumatra. Ten thousand times bigger than Mt St Helens, it created a global catastrophe dramatically affecting life on Earth. Scientists know that another one is due - they just don't know when... or where.

Yellowstone National Park: It is little known that lying underneath one of America's areas of outstanding natural beauty - Yellowstone Park - is one of the largest supervolcanoes in the world. Scientists have revealed that it has been on a regular eruption cycle of 600,000 years. The last eruption was 640,000 years ago... so the next is overdue.

And the sleeping giant is breathing: volcanologists have been tracking the movement of magma under the park and have calculated that in parts of Yellowstone the ground has risen over seventy centimetres this century. Is this just the harmless movement of lava, flowing from one part of the reservoir to another? Or does it presage something much more sinister, a pressurised build-up of molten lava?

Scientists have very few answers, but they do know that the impact of a Yellowstone eruption is terrifying to comprehend. Huge areas of the USA would be destroyed, the US economy would probably collapse, and thousands might die.

And it would devastate the planet. Climatologists now know that Toba blasted so much ash and sulphur dioxide into the stratosphere that it blocked out the sun, causing the Earth's temperature to plummet. Some geneticists now believe that this had a catastrophic effect on human life, possibly reducing the population on Earth to just a few thousand people. Mankind was pushed to the edge of extinction... and it could happen again.

When and how did space and time begin? The birth of the Universe is one of the biggest mysteries in astronomy. It has perplexed the best scientific minds for centuries. Decades before space travel was possible, astronomers dreamed of putting a telescope into orbit to try and answer these fundamental questions. It wasn't until the 1970s, when space flight had become a reality, that NASA resolved to build just such a space telescope. They named it Hubble.

This was one of the most ambitious missions ever conceived. The technical challenges were enormous and it took 12 years to design and build. Travelling at seventeen thousand miles an hour, the Hubble Telescope would take pictures of the furthest reaches of space, transmitting them 400 miles back to Earth.

In April 1990 the Hubble Space Telescope was launched. But just weeks later, disaster struck - the $2 billion telescope had a fatal flaw in its main mirror. This was not just a disaster for NASA; it was a national scandal. Hubble had to be saved; scientists and engineers began to search desperately for a solution to the problem.

Plans for an adventurous repair mission began to take shape but it was two years before work could be carried out. It took astronauts five gruelling space-walks to carefully replace the instruments and patch up the telescope. But nobody knew if Hubble would be able to deliver on any of its original promises.

Finally, the miracle happened. An unexpected avalanche of data from Hubble confirmed that the telescope was fixed. At last it began to solve the most fundamental puzzles of the Universe.

Hubble has given us breathtaking images of the birth of stars; it has found black holes swallowing matter at the centre of galaxies; and last year the Hubble Telescope resolved the most fundamental question in astronomy - the age of the Universe. At last, half a century of scientific endeavour was rewarded.

Horizon marks the 10th anniversary of the launch of the Hubble Space Telescope by tracing the extraordinary tale of triumph, disaster and eventual success of this unique window into the Universe.

What happens when a completely healthy person wants their leg amputated?

Gregg is 55 and does not feel physically whole. This is despite the fact that he is physically healthy and able-bodied. Gregg believes he is incomplete with two legs and it has been his life-long struggle to get doctors to agree that removing one of his legs is the right thing for him. He isn't delusional. He knows what he is asking for and knows it is strange. But he cannot help his feelings. Gregg suffers from a rare but genuine psychological disorder - a form of body dysmorphia. And Gregg is not alone.

Although Body Dysmorphia is rare, a worldwide network of sufferers is growing and demanding treatment. It affects both men and women and each person has a precise sense of which limb or limbs they want removed.

Cases were cited a hundred years ago but still very little is known about the disorder. No one knows what causes it and very few psychiatrists have even encountered patients with the disorder. All that the patients seem to have in common is a strong memory of the first amputee they saw. They also report that the feelings started in childhood. However, the profession is now being forced to respond and devise methods of treatment. If not treated, it has been reported that suffers can go to extreme lengths to remove the unwanted limbs themselves. Some have even committed suicide.

The difficulty with the condition is that the conventional methods for treating psychological problems, drugs and therapy, do not seem to be effective. The only treatment that does seem to be effective is surgery - actually removing the limb. The idea of using surgery is highly controversial and has divided the medical community. Some physicians consider it much too drastic a measure, possibly conflicting with their Hippocratic oath, not to cause harm. Others believe that it is the only way to free the patient of their obsession, 'curing' them of their psychological problem.

At the present time, there is only one surgeon in Britain who has been prepared to perform such operations and who has publicly defended his decision. He has operated on two patients, both of who claim to be delighted with their new body-image and now free to get on with the rest of their lives.

There are many other patients who seek similar treatment. Horizon 'Complete Obsession' follows a year in the lives of people who are body dysmorphic and are determined to have their limbs surgically removed. It follows the process they go through to try and achieve their goal.

Some people see GM food as a ground-breaking scientific idea that could help to end world hunger and reduce global pollution. Others see it purely as 'Frankenstein foods' on 21st century menus, bringing health and environmental disasters. But what are the real scientific facts behind the newspaper headlines?

Scientists can manipulate the genetic code of life to produce plants with new characteristics never seen in nature. They can isolate any one gene from any organism like an animal or bacterium, and insert it into a completely unrelated species like a plant. The possibilities are almost endless - Scientists can insert a gene from a bacterium into a grape to make it resistant to viruses. Or they can engineer maize that resists drought or potatoes that resist pests, so farmers can use less pesticides on their crops.

For thousands of years we have been tampering with the genes of plants by traditional breeding. But there's a key difference here - with traditional plant breeding genes cross within the same species. But GM allows plant breeders to break the species barrier. And for critics this is fundamentally unnatural.

The fear is that the proteins produced by these foreign genes might be dangerous. Either because the protein itself is poisonous or because it might alter the chemistry of the plant so that the plant becomes toxic. Detailed tests are performed on the plants to discover if they are substantially biologically and chemically the same as before modification and if they have become toxic or allergenic.

Critics believe that no amount of testing can ensure that GM crops are completely safe. They believe that there is too much we don't understand about the complex genetic make-up of living organisms. And that even though there is little evidence so far, there may be a risk that genetic modification could cause effects so unexpected that they will be missed by all the tests biotech scientists carry out.

In contrast genetic engineers claim their work is safer and more predictable because they are moving just one or two specific genes, and they can more easily test the effects.

But those who campaign against GM have another fear: that the genes from the engineered plant will spread throughout the plant world, creating new strains of superweed and superbug we cannot control.

Horizon explores the key elements of scientific facts to try to answer the ultimate question: do the dangers of GM foods outweigh their benefits?

If extra-terrestrials do exist they must have a home. Horizon tells the story of the race to find out where in the Universe this might be. The answer, for scientists across the world, lies in the hunt for planets around distant stars.

Stars which are trillions of miles away from our own solar system.

But the history of the planet hunters is littered with failure. Centuries of searching had thrown up nothing. It was time for the new style planet hunters to step in. However, it is only in the last ten years that these scientists have had the technology to succeed. Even now looking for these distant planets is far from straightforward.

The planets themselves are so faint that they cannot be seen, even by the most powerful telescopes ever built. Instead the astronomers must devise ingenious ways to search for clues to their presence. They examine stars just like our own Sun, across the galaxy, for any give-away characteristics that might indicate that they too have planets circling around them.

A Swiss team finally struck gold in 1995 - convinced they'd detected a star that must have its own planet. Their discovery was the first of its kind but not the last. Other teams started to get lucky and suddenly it seemed like there were stars with planets everywhere. But the scientific community soon became restless. All they had done so far was detect the presence of alien planets - without seeing one, it was impossible to work out what the planet was like.

If these planets really did exist it was time the scientists caught a glimpse of one of them. Only then would they be able to learn about the planet - its surface and its atmosphere. And only then would they know whether it could sustain life as we know it.

Horizon follows the trials and tribulations of the planet hunters and shares in the triumph of the Scottish team who, just a few months ago, became the first to achieve the ultimate goal - to capture the image of an alien planet. It is orbiting another star, 55 light years away from Earth.

The question is - how similar is this planet to our own and could it be home to alien life? Horizon uncovers the answers.

A handful of children around the world cannot tolerate the sun. Any exposure leads rapidly to skin cancer. They must either play indoors during daylight or be protected from head to toe in UV-proof suits. These children suffer from a strange and rare genetically-inherited disease, xeroderma pigmentosum, or XP, which means that within seconds of the sun's rays touching their skin, they are in danger of developing skin cancer.

Sun Children with XP are missing the crucial gene that repairs damage to DNA and so exposure to any carcinogen - UV light, or even cigarette smoke - is lethal. Unless, they are thoroughly protected they will die from cancer at an early age. There is no cure.

But these tragic children may may lead the way to new and better cancer treatment. Through studying XP sufferers, scientists have reached a whole new understanding of the genetic basis of cancer. They can now predict why one in three people will succumb to cancer. Scientists have discovered how the body survives damage and repairs itself and as a result of this, developed a radical new approach to treating cancer.

Horizon explores the story of one family, where 5 out of 7 siblings suffer from XP, and how they provide the final proof that genes and DNA repair are linked to cancer. It follows an intricate 40-year scientific detective story from the discovery of DNA, through the chance findings of the cells of the XP families that led to the unexpected insight that DNA is capable of repairing itself and that the failure of this repair system underlies most cancers.

After years of research, this insight is finally beginning to revolutionise medicine. Now a new concept in cancer drug therapy is just beginning medical trials based on the knowledge gained from children suffering from XP.

Scattered across the world’s oceans are a handful of rare geological time-bombs. Once unleashed they create an extraordinary phenomenon, a gigantic tidal wave, far bigger than any normal tsunami, able to cross oceans and ravage countries on the other side of the world. Only recently have scientists realised the next episode is likely to begin at the Canary Islands, off North Africa, where a wall of water will one day be created which will race across the entire Atlantic ocean at the speed of a jet airliner to devastate the east coast of the United States. America will have been struck by a mega-tsunami.

Back in 1953 two geologists travelled to a remote bay in Alaska looking for oil. They gradually realised that in the past the bay had been struck by huge waves, and wondered what could have possibly caused them. Five years later, they got their answer. In 1958 there was a landslide, in which a towering cliff collapsed into the bay, creating a wave half a kilometre high, higher than any skyscraper on Earth. The true destructive potential of landslide-generated tsunami, which scientists named "Mega-tsunami", suddenly began to be appreciated. If a modest-sized landslide in Alaska could create a wave of this size, what havoc could a really huge landslide cause?

Scientists now realise that the greatest danger comes from large volcanic islands, which are particularly prone to these massive landslides. Geologists began to look for evidence of past landslides on the sea bed, and what they saw astonished them. The sea floor around Hawaii, for instance, was covered with the remains of millions of years’ worth of ancient landslides, colossal in size.

But huge landslides and the mega-tsunami that they cause are extremely rare - the last one happened 4,000 years ago on the island of Réunion. The growing concern is that the ideal conditions for just such a landslide - and consequent mega-tsunami - now exist on the island of La Palma in the Canaries. In 1949 the southern volcano on the island erupted. During the eruption an enormous crack appeared across one side of the volcano, as the western half slipped a few metres towards the Atlantic before stopping in its tracks. Although the volcano presents no danger while it is quiescent, scientists believe the western flank will give way completely during some future eruption on the summit of the volcano. In other words, any time in the next few thousand years a huge section of southern La Palma, weighing 500 thousand million tonnes, will fall into the Atlantic ocean.

What will happen when the volcano on La Palma collapses? Scientists predict that it will generate a wave that will be almost inconceivably destructive, far bigger than anything ever witnessed in modern times. It will surge across the entire Atlantic in a matter of hours, engulfing the whole US east coast, sweeping away everything in its path up to 20km inland. Boston would be hit first, followed by New York, then all the way down the coast to Miami and the Caribbean.

Conjoined twins are among the rarest of human beings. There are probably fewer than a dozen adult pairs living in the world today. Only a few hundred pairs of conjoined twins are born in the whole world each year - they appear about once in every 100,000 births - but more than half of them are stillborn, and one in three live for only a few days.

Of those who survive, a very small number will be selected for separation surgery. But as there are few hospitals with the skills and experience to perform this kind of surgery, separation is still a very unusual event. The harrowing decisions which surgeons have to make when faced with conjoined twins have been highlighted by the recent case in Manchester, England. Separating conjoined twins is not only technically challenging; it can involves life and death decisions about whether one twin should be sacrificed in the hope of saving the other. But "sacrifice surgery" has a poor record of success, and the Manchester case is the latest round in an international debate about the value of separation operations.

The confidence of the surgeons, who believe that separation is essential, is challenged by medical historian, Dr Alice Dreger of Michigan State University. She argues that twins themselves might take a different view - if they were ever given a chance to express it.

Horizon interviews two pairs of adult conjoined twins - Lori and Reba Schappell in Pennsylvania and Masha and Dasha Krivoshlyapova in Moscow. Lori and Reba are joined at the head; Masha and Dasha are joined in their lower body. They say that they prefer their conjoined lives, despite the problems and challenges, rather than face the risks of separation surgery.

Lori and Reba live independent lives in their own apartment in Pennsylvania; Lori enjoys working with computers and Reba is developing a career as a country singer. Masha and Dasha had a difficult childhood; they were subjected to medical experimentation when they were very young and hidden away from the public. Since the end of the communist era they have been able to tell their story. Their autobiography is being written by a British journalist, Juliet Butler.

Horizon also follows surgeons at the Red Cross Children's Hospital in Cape Town, Africa as they plan to separate eight month old twins, Stella and Esther Alphonce. The baby girls are joined at the hip, and the surgeons have little doubt that they can and should be separated, even though the operation carries risks of disability for the twins. Historically conjoined twins who were not, or could not be separated have lived successful lives, even if this involved putting themselves on public display. The original Siamese twins, Chang and Eng Bunker, were joined by a narrow strip of flesh and could easily be separated today.

Like Millie and Christine McCoy, who also lived in the USA in the middle of the last century, they earned fame and fortune touring the world. But life for conjoined twins has never been easy, Millie and Christine were kidnapped and sold several times in their childhood. The British conjoined twin sisters, Violet and Daisy Hilton, provoked a scandal in the USA when one of them tried to get married. They did eventually marry, but they were never separated. The tragedy for conjoined twins who spend their lives together is that they inevitably die together too. When one twin dies, the heart of the other twin keeps pumping until he or she is drained of blood.

Is this another reason why twins should be separated when they are young? There are no simple answers, because every pair of twins is unique.

On August 2nd 1947, a British civilian version of the wartime Lancaster bomber took off from Buenos Aires airport on a scheduled flight to Santiago. There were 5 crew and 6 passengers on board the plane - named "Stardust". But Stardust never made it to Santiago. Instead it vanished when it was apparently just a few minutes from touchdown. One final strange Morse code radio message - "STENDEC" - was sent, but after that nothing more was heard from the plane. Despite a massive search of the Andes mountains no trace of the plane was ever found. For 53 years the families of those who disappeared have not known what happened to their loved ones. But earlier this year the plane suddenly reappeared on a glacier high up in the Andes, more than 50 km’s from the area where the plane was last reported.

In the summer of 2000, one of the great frontier cities of the Roman Empire, the city of Zeugma, all but disappeared from the face of the Earth under the flood waters of a dam. In a bid to modernise, the Turkish government has embarked on one of the most ambitious engineering projects in the world, building a series of dams on the Euphrates over the past twenty years. Almost every dam threatens ancient remains that lie below in one of the most archaeologically rich regions of the world. The completion of the Birecik dam, featured in this film, has flooded the valley where Zeugma is buried. The city on the flat plain has entirely disappeared and the waters have now risen to cover 30% of the city on the hillside.

Horizon tells the story of the archaeologists' fifth and final visit, struggling to save what they could before the dam waters rose. It witnesses the uncovering of some of the most beautiful examples of Roman art ever found. The team’s discoveries at Zeugma caused an international outcry and further excavations were hurriedly put together.

Since 1995, French archaeologists Pierre Leriche and Catherine Abadie-Reynal have taken up the challenge to save what they can from the city before the dam is finished. The archaeologists have two main tasks - to uncover the history of this desperately under-excavated region of Turkey and to remove what treasures they could from the site before they were lost forever. On this, their final excavation, they had to work against the clock: they only had a permit to dig for six weeks

Zeugma was founded by one of Alexander the Great’s generals, Seleucia Nicator, and prospered under later Roman rule. It became one of the major cities of the Roman eastern frontier with a garrison of over 6,000 soldiers. The city’s bridge across the Euphrates made it one of the most critical trading cities in the region, on the silk routes to the East. The archaeologists know that the city contains vital clues to the history of the region. Previously looted exquisite mosaics have hinted at the treasures of its past that must be buried somewhere in the vast site.

The part of the old city on the Euphrates flood plain, Apamea, was the first to go. But the archaeologists didn’t stand a chance of excavating it in such a short amount of time. So using a technology originally developed for finding oil and mineral deposits, they instead generated a picture of the buried city just as it lies below ground. They discovered a preserved ancient Greek city, laid out in a perfect grid. Meanwhile, in the remains of a Roman villa across the river, the archaeologists had an extraordinary stroke of luck.

With only five days left on the excavation permit, Catherine Abadie-Reynal unearthed a masterpiece: a beautiful Roman mosaic floor. The discovery caused an international outcry and hit the headlines across the world. The archaeologists were granted more days to excavate, but they could not stem the tide of the dam project.

With time running out, they uncovered more stunning mosaics in the villa. They were dug out from the site and sent to a local museum at Gaziantep - just in time. By mid June 2000, the newly uncovered fourteen room villa disappeared underwater. By October, the level of the water finally settled to form a vast, still lake in the valley. All excavations at the site ceased.

There's recently been a move by the Turkish government to declare Zeugma a site of special archaeological interest. The remainder of the ancient city on the hillside could, in theory, still be explored.

The dam will not only erase much of Zeugma from history. It will also displace 30,000 people, mostly Kurds, from the villages they have lived in for generations. For many, the loss of Zeugma is a tragedy.

At the heart of the AIDS epidemic in Africa, there is a deadly mystery that has puzzled scientists for years. There are groups of people who are four times less likely to get HIV than other people, sometimes living just yards away, across a single valley - people with apparently similar behaviour and lifestyle. Scientists realised that if they could understand why these people are so much less vulnerable to the HIV virus, it might lead to an answer that could save millions of lives. And after 15 years of detective work it turns out there may be a remarkably simple answer: the high risk areas for HIV coincide with tribes who are uncircumcised. In Africa, it seems a man is much more likely to get HIV if he is uncircumcised.

In Kaoma, Western Zambia, a young boy is on his way to the sacred Mukondaa - the tribal circumcision ground. Around him the tribal elders are gathered, dressed in their ceremonial garb, and vivid masks. But the young boy himself is an outsider, not from this tribe, and none of his relatives or ancestors have ever been circumcised. In fact, his parents are only prepared to break the taboo of their own tribe because they believe that circumcision could save his life by protecting him from AIDS. At first sight this belief seems like the kind of superstition to which desperate people often turn in times of plague. But now there is scientific evidence that suggests these people could well be right.

There have now been twenty seven statistical studies that show a big difference in HIV infection between circumcised and uncircumcised men. For example, among the uncircumcised people of Kisumu in Western Kenya, a man is three times as likely to get AIDS than his circumcised neighbours. Among truck drivers in Mombasa the difference is four-fold.

Horizon travels across Africa, tracing the work of scientists who have unearthed the statistical data behind this correlation. At the same time microbiologists have been battling to understand the complex and insidious virus, and their work indicates that the foreskin may be a key entry point for HIV. The logical conclusion for these scientists is that if you remove the foreskin, you begin to protect the man. No-one believes that circumcision can protect completely - the evidence so far only indicates that it reduces the risk of infection by HIV, and then only during heterosexual sex. Unquestionably, condoms are still the best protection. But in the many countries where the use of condoms is minimal, it seems that circumcision might help to reduce the spread of AIDS.

In the absence of a vaccine for AIDS, and the lack of condom use in the developing world, should governments think the unthinkable and encourage the circumcision of young boys in non-circumcising tribes as a public policy? Opposing this idea are the voices of tribal elders who are loath to change tribal traditions that have existed for generations, and a fierce Western anti-circumcision lobby which believes that circumcision is a form of mutilation and violates basic human rights.

Amazing new discoveries in South America are revolutionising what we thought we knew about the dinosaur world. It now seems that South America was home to both the largest meat-eater - so new it's still without a name - and the largest herbivore - the enormous long-necked Argentinasaurus. And what's more, these dinosaurs lived at the same time in the same place. So it's possible that like in a science fiction movie, in this prehistoric world these two giants of their kind fought each other in a spectacular clash of the Titans.

Horizon follows the scientists to Argentina as they unearth one of these giants - a brand new species of dinosaur; the biggest carnivore ever discovered. Not yet named, this new creature is even bigger than T. rex, the so-called 'king' of the carnivores. The new giant South American predator had a skull bigger than a man that was full of serrated, knife-like teeth and long powerful jaw muscles. They could dissect their prey with almost surgical precision.

But even this formidable killing machine couldn't alone have taken on the massive long-neck, Argentinasaurus, which was the height of a five-storey building. It must have hunted in a pack. The problem is, the mega-meat-eaters have always been assumed to have been solitary creatures. The evidence shows that they lived and hunted alone. If they weren't pack hunters, then they would never have attacked Argentinasaurus. So it looked like the idea of a mighty battle between these two giants was simply science fiction. But extraordinary new clues are proving otherwise.

Palaeontologist Phil Currie had long suspected that the giant carnivores might indeed have hunted in packs and he set out to find the proof. Only now after many years' work have Currie and his team unearthed the clues that are beginning to convince other palaeontologists that the huge carnivorous dinosaurs hunted in groups. With the help of his colleague Rodolfo Coria, Currie has discovered not one but two fossil bone-beds showing packs of massive carnivorous dinosaurs that have lain buried for millions of years. Each pack - one found in the badlands of Alberta, Canada and the other in Patagonia, Argentina - contains a whole range of individuals, from young through to fully mature adults indicating that they lived alongside in a herd. He's convinced that these dinosaurs were buried together because they were living together.

These new finds are good evidence that these creatures really did hunt as a team. And that means a ferocious pack of enormous carnivorous dinosaurs roaming the lands of South America may indeed have taken on a huge Argentinasaurus in a fight to the death. So it may not just be science fiction - the Clash of the Titans could have happened after all.

In June 2000, astronomers made an extraordinary discovery. One that promises to solve one of the biggest problems in cosmology - how and why galaxies are created. Incredibly, the answer involves the most weird, destructive and terrifying objects in the Universe - supermassive black holes. Scientists are beginning to believe that these forces of pure destruction actually help trigger the birth of galaxies and therefore are at the heart of the creation of stars, planets and all life. Supermassive black holes are so extraordinary that until recently, many people doubted that they existed at all. The idea of giant black holes the size of the Solar System seemed more like science fiction that reality - such monsters would be so powerful that they could destroy the very fabric of the Universe. But in the last five years a series of discoveries has changed our understanding of supermassive black holes and galaxies forever. Using the powerful Hubble Space Telescope, scientists have been scanning nearby galaxies, searching for these giant black holes. It's a difficult job - by their very nature black holes swallow light - so can never be seen. So what scientists have been looking for is the effect of their massive gravity, hurling stars around them at immense speed. What they've found is more extraordinary than anyone could ever have imagined; not just evidence that these vast destructive monsters exist… but so far they're in every single galaxy toward which they have turned their telescopes. These giant agents of destruction appear to be common throughout the Universe. Scientists now think supermassive black holes are a fundamental part of what a galaxy actually is. Lurking at the heart of every single galaxy is a giant black hole of apocalyptic proportions - and that includes our own galaxy, the Milky Way. Astronomer Andrea Ghez has been studying the heart of the Milky Way for the last five years. What she's discovered is irrefutable evidence for a giant black hole, 3 billion times the size of our own sun. A black hole that could destroy the entire Solar System. And as Horizon was filming in July 2000, Ghez got some terrifying images - of the giant monster sucking up gas and stars at the galaxy heart. So what is this giant monster doing at the heart of our galaxy? What effect will this giant black hole 25,000 light years away have on us and the rest of the galaxy around it? These are questions that have been puzzling astronomers for the last few years - and in June, two separate groups of scientists found evidence that points to a startling answer. Rather than being destructive parasites, it seems that supermassive black holes may be essential in the very creation of the galaxies they live in. Exactly how our galaxy was created has mystified astronomers and physicists for years. Although there have been many theories, there's little evidence to explain how the gas in the early Universe condensed to form the galaxy we see today. Now scientists realise they've been missing a vital ingredient - a supermassive black hole. The immense gravity of a giant black hole might trigger the gas to collapse in the first place. By churning up the gas around it, a giant black hole would trigger the birth of stars, planets and life itself. Despite being the most destructive thing in the Universe, scientists now think our supermassive black hole could be crucial in creating the galaxy as we know it. The supermassive black hole in our own galaxy may be the reason we exist, but recent work suggests it may also be our end. At present Earth is so far away from the black hole that it can't affect us, but physicist John Dubinski thinks all that could change. In January 2000 he graphically simulated the final fate of our galaxy. In 3 billion years we will collide with the next door galaxy, Andromeda. The resulting apocalypse will force the Earth and our Solar System out of orbit. Dubinski has calculated a worrying 50:50 chance that we'll be sent hurtling in towards the black hole at the centre of this maelstrom. This would be fatal for the Earth.

In 1965 in the Canadian town of Winnipeg, Janet Reimer gave birth to twin boys - Bruce and Brian. Six months later a bungled circumcision left Bruce without a penis. Based on a radical new theory of gender development the decision was taken to raise Bruce as a girl. In 1967 Bruce became Brenda and for the next three decades this case would be at the heart of one of the most controversial theories in the history of science.

The man behind this work was world-renowned psychologist Dr John Money. In the 1950s Dr Money developed a theory that revolutionised our understanding of gender. Money believed that what he called our 'gender identity' - what makes us think, feel and behave as boys or girls - is not fully formed by the time of birth. While we may have some innate sense of being a boy or a girl, for up to two years after birth, our brains are, in effect, malleable and we can be taught to grow up as either a boy or girl by how we are raised - by the toys we are given, the guidance we receive from adults and the clothes we are given to wear. This became known as the 'theory of gender neutrality'.

Dr Money had reached this conclusion by working with a rare group of individuals born with ambiguous genitals - people known as intersexuals or hermaphrodites. Dr Money studied groups of intersex children, and concluded that these children could be brought up as either boys or girls regardless of their genetic or physical sex. The legacy of Dr Money's work was a revolution in the treatment of 'intersex'. From the 1950s to the present day many intersex children born with a tiny penis are reassigned as female even if they are actually genetically male.

But not everyone agreed with Dr Money's theories. Since the 1950s a small group of scientists including Dr Milton Diamond have questioned John Money's work. Diamond believed that our sex is already defined in our brains before we are born. He was convinced that the power of our genes and hormones was so strong that no amount of nurturing could override them.

But John Money's theory had already become firmly accepted around the world and the most dramatic confirmation of the theory came from one particular case - the case of Bruce Reimer.

Bruce was a normal boy, not an intersex child, and yet the decision was made to turn this boy who had lost his penis, into a girl. Under the guidance of Dr Money and his team at Johns Hopkins University this baby boy was surgically changed into a girl. After surgeons at Hopkins had castrated baby Bruce, he became baby Brenda. The family were instructed how to bring up Brenda as a normal little girl. According to Dr Money's theory she would grow up believing herself to be female and would go on to live a normal happy life as a woman. It seemed the ultimate test that nurture could override nature.

Thirty years after Bruce became Brenda, the impact of this extraordinary story continues. After almost 14 years living as a female, Brenda Reimer reverted to her true biological sex - the case of the boy who was turned into a girl had failed. Brenda took the name David and for the last twenty years he has lived anonymously in his hometown of Winnipeg. For almost all this time no one knew the outcome of John Money's celebrated case. But now that David has gone public, the case is being widely discussed once again and its impact on John Money's theory of gender development and the treatment of intersex children is being hotly debated.

Horizon puts Graham Hancock's controversial theories about the past to the test, dissecting his evidence for a lost civilisation.

Graham Hancock offers various pieces of evidence to support his theory. He claims that the mysterious lost civilisation left its mark in ancient monuments, which he calculates were built to mirror certain constellations of stars. His hugely popular ideas have attracted such a wide audience that they stand to replace the conventional view of the past, which is based on scientific evidence that the civilisations of the ancient world were developed independently, by different peoples, on different continents.