The world is affected by an obesity epidemic, but why is it that not everyone is succumbing? Medical science has been obsessed with this subject and is coming up with some unexpected answers. As it turns out, it is not all about exercise and diet. At the centre of this programme is a controversial overeating experiment that aims to identify exactly what it is about some people that makes it hard for them to bulk up.

For centuries scientists have been attempting to come up with an elixir of youth. Now remarkable discoveries are suggesting that ageing is something flexible that can ultimately be manipulated. The scientists 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 real key to controlling how we age lie with a five-year-old boy with an extraordinary ageing disease or with a self-experimenting Harvard professor? Could one of these breakthroughs really see our lives extend past 120 years?

Sir David Attenborough reveals plants as they have never been seen before - on the move and dangerously devious. About the major problems of life - growing, finding food, reproduction - and the varied ways plants have evolved to solve it. Filmed from the plant's point of view, using computer animations, fibre-optics and unique time-lapse photography. The first episode looks at how plants are able to move". The bramble is an aggressive example: it advances forcefully from side to side and, once settled on its course, there is little that can stand in its way. An altogether faster species is the birdcage plant, which inhabits Californian sand dunes. When its location becomes exposed, it shifts at great speed to another one with the assistance of wind — and it is this that allows many forms of vegetation to distribute their seeds. While not strictly a plant, the spores of fungi are also spread in a similar fashion. One of the most successful (and intricate) flowers to use the wind is the dandelion, whose seeds travel with the aid of 'parachutes'. They are needed to travel miles away from their parents, who are too densely packed to allow any new arrivals. Trees have the advantage of height to send their seeds further, and the cottonwood is shown as a specialist in this regard. The humidity of the tropical rainforest creates transportation problems, and the liana-species Alsomitra macrocarpa is one plant whose seeds are aerodynamic 'gliders'. Some, such as those of the sycamore, take the form of 'helicopters', while others, such as the squirting cucumber release their seeds by 'exploding'. Water is also a widely used method of propulsion. The tropical sea bean Entada gigas has one of the biggest fruits of all plants and is dispersed by water streams. However, most plants use living couriers, whether they be dogs, humans and other primates, ants or birds, etc., and to that end, they use colour and smell to signify when they are ripe for picking.

For centuries, man has yearned for an earthly paradise, and no place better encapsulates this desire than Shangri-La - but was it ever real? The tale of an earthly paradise is among the most enduring myths in the world. From Sumerian epic to the 'islands of the blest' in Celtic literature, it has been a recurring theme through many bodies of literature and for thousands of years. Not surprisingly, then, modern people have also been drawn to the dream of a lost paradise where the ravages of time and history have been held back, where human beings live in harmony with nature, and where the wisdom of the planet is saved for future generations. In other words, to a Shangri-La.

The tale of the strongest superhero in Greek mythology and his quest for redemption. To atone for committing a heinous crime, Hercules embarks on a series of impossible challenges known as the 12 Labors. Hercules endures as one of history's most influential demi-Gods, but recent archaeological discoveries suggest that mythology's strongest man may have been inspired by a real person.

Iain explores man's relationship with fire. He begins by embarking on an extraordinary encounter with this terrifying force of nature - a walk right through the heart of a raging fire. Fire has long been our main source of energy and Iain shows how this meant that the planet played a crucial role in Britain's industrial revolution, whilst holding China's development back. Along the way he dives in a mysterious lake in Oregon, climbs a glacier of salt, crawls through an extraordinary cave in Iran and takes a therapeutic bath in crude oil.