Alcohol is by far the most widely used drug - and a dangerous one at that. So why are so many of us drinking over the recommended limits? Addiction expert John Marsden, who likes a drink, makes a professional and personal exploration of our relationship with alcohol. He undergoes physical and neurological examinations to determine its impact, and finds out why some people will find it much harder than others to resist alcohol.

With the help of a hammer-wielding scientist, Jennifer Aniston and a general anesthetic, Professor Marcus du Sautoy goes in search of answers to one of science's greatest mysteries: how do we know who we are? While the thoughts that make us feel as though we know ourselves are easy to experience, they are notoriously difficult to explain. So, in order to find out where they come from, Marcus subjects himself to a series of probing experiments. He learns at what age our self-awareness emerges and whether other species share this trait. Next, he has his mind scrambled by a cutting-edge experiment in anesthesia. Having survived that ordeal, Marcus is given an out-of-body experience in a bid to locate his true self. And in Hollywood, he learns how celebrities are helping scientists understand the microscopic activities of our brain. Finally, he takes part in a mind-reading experiment that both helps explain and radically alters his understanding of who he is.

The potential of stem cells for the future of medicine seems scarcely plausible. They offer the prospect of a new 'regenerative medicine' that may before long be able to regrow amputated limbs, create hearts in a lab or heal people paralyzed by spinal cord injuries. It's that huge. But because we're just at the point where some of that promise translates into clinical procedures, there are vultures around -unregulated doctors who play on patients' hopes via glossy websites. This Horizon documentary, called Fix Me, follows Sophie Morgan, paralyzed from the waist down in a car accident, as she sets out to discover if there's a treatment out there for her, or whether the claims are too good to be true. It's an enlightening journey, as are those of the two other subjects - an amputee, Anthony, and Dean, a man with a potentially fatal heart condition.

Black holes are one of the most destructive forces in the universe, capable of tearing a planet apart and swallowing an entire star. Yet scientists now believe they could hold the key to answering the ultimate question - what was there before the Big Bang? The trouble is that researching them is next to impossible. Black holes are by definition invisible and there's no scientific theory able to explain them. Despite these obvious obstacles, Horizon meets the astronomers attempting to image a black hole for the very first time and the theoretical physicists getting ever closer to unlocking their mysteries. It's a story that takes us into the heart of a black hole and to the very edge of what we think we know about the universe.

Talking is something that is unique to humans, yet it still remains a mystery. Horizon meets the scientists beginning to unlock the secrets of speech - including a father who is filming every second of his son's first three years in order to discover how we learn to talk, the autistic savant who can speak more than 20 languages, and the first scientist to identify a gene that makes speech possible. Horizon also hears from the godfather of linguistics, Noam Chomsky, the first to suggest that our ability to talk is innate. A unique experiment shows how a new alien language can emerge in just one afternoon, in a bid to understand where language comes from and why it is the way it is.

Alan Davies attempts to answer the proverbial question: how long is a piece of string? But what appears to be a simple task soon turns into a mind-bending voyage of discovery where nothing is as it seems. An encounter with leading mathematician Marcus du Sautoy reveals that Alan's short length of string may in fact be infinitely long. When Alan attempts to measure his string at the atomic scale, events take an even stranger turn. Not only do objects appear in many places at once, but reality itself seems to be an illusion. Ultimately, Alan finds that measuring his piece of string could - in theory at least - create a black hole, bringing about the end of the world.

In his lengthy career, Sir David has watched the human population more than double from 2.5 billion in 1950 to nearly seven billion. He reflects on the profound effects of this rapid growth, both on humans and the environment. While much of the projected growth in human population is likely to come from the developing world, it is the lifestyle enjoyed by many in the West that has the most impact on the planet. Some experts claim that in the UK consumers use as much as two and a half times their fair share of Earth's resources. Sir David examines whether it is the duty of individuals to commit not only to smaller families, but to change the way they live for the sake of humanity and planet Earth.

We have an extraordinary relationship with dogs - closer than with any other animal on the planet. But what makes the bond between us so special? Research into dogs is gaining momentum, and scientists are investigating them like never before. From the latest fossil evidence, to the sequencing of the canine genome, to cognitive experiments, dogs are fast turning into the new chimps as a window into understanding ourselves. Where does this relationship come from? In Siberia, a unique breeding experiment reveals the astonishing secret of how dogs evolved from wolves. Swedish scientists demonstrate how the human/dog bond is controlled by a powerful hormone also responsible for bonding mothers to their babies. Why are dogs so good at reading our emotions? Horizon meets Betsy, reputedly the world's most intelligent dog, and compares her incredible abilities to those of children. Man's best friend has recently gone one step further - helping us identify genes responsible for causing human diseases.

Just months ago, the world stood in fear of an emerging new disease that threatened tohug millions. A new flu variant H1N1 had arrived. In the UK alone, 65,000 passings were predicted. Yet to date, these dire warnings have not materialised. If this latest pandemic has taught anything, it is just how little is understood about the invisible world of viruses. But that has not stopped scientists trying. Horizon follows the leading researchers from across the world, who are attempting to unravel the many secrets of viruses to understand when and why theyhug.

Over a person's lifetime they are likely to be prescribed more than 14,000 pills. Antibiotics, cholesterol lowering tablets, anti-depressants, painhuggers, even tablets to extend youth and improve performance in bed. These drugs perform minor miracles day after day, but how much is really known about them? Drug discovery often owes as much to serendipity as to science, and that means much is learnt about how medicines work, or even what they do, when they're taken. By investigating some of the most popular pills people pop, Horizon asks, how much can they be trusted to do what they are supposed to?

For centuries scientists have been attempting to come up with an elixir of youth. Now remarkable discoveries are suggesting that aging is something flexible that can ultimately be manipulated. Horizon meets the scientists who are attempting to piece together why we age and more vitally for all of us, what we can do to prevent it. But which theory will prevail? Does the 95-year-old woman who smokes two packets of cigarettes a day hold the clue? Do blueberries really delay signs of aging or is it more a question of attitude? Does the real key to controlling how we age lie with a five-year-old boy with an extraordinary aging disease or with a self-experimenting Harvard professor? Could one of these breakthroughs really see our lives extend past 120 years?

By our third year, most of us will have learned to count. Once we know how, it seems as if there would be nothing to stop us counting forever. But, while infinity might seem like an perfectly innocent idea, keep counting and you enter a paradoxical world where nothing is as it seems. Mathematicians have discovered there are infinitely many infinities, each one infinitely bigger than the last. And if the universe goes on forever, the consequences are even more bizarre. In an infinite universe, there are infinitely many copies of the Earth and infinitely many copies of you. Older than time, bigger than the universe and stranger than fiction. This is the story of infinity.

Could you have come up with Einstein's theory of relativity? If not - why not? This is what Marcus du Sautoy, professor of mathematics, wants to explore. Marcus readily admits that he is no genius, but wants to know if geniuses are just an extreme version of himself - or whether their brains are fundamentally different. Marcus meets some remarkable individuals - Tommy, an obsessive artist who uses his whole house as his canvas; Derek: blind, autistic, and a pianist with apparently prodigious gifts; Claire who is also blind, but whose brain has learned to see using sound. Marcus is shown how babies have remarkable abilities which most of us lose as teenagers. He meets a neuroscientist who claims he has evidence of innate ability, a scientist who's identified a gene for learning, and Dr. Paulus, who has discovered how to sharpen the brain... by electrically turbo-charging it.

We are the only species on earth that cooks its food - and we are also the cleverest species on the planet. The question is: do we cook because we're clever and imaginative, or are we clever and imaginative because our ancestors discovered cooking? Horizon examines the evidence that our ancestors' changing diet and their mastery of fire prompted anatomical and neurological changes that resulted in taking us out of the trees and into the kitchen.

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