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.

Sir David Attenborough investigates whether the world is heading for a population crisis. 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. 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.

It's a voyage of exploration like no other - to Titan, Saturn's largest moon and thought to resemble our own early Earth. For a small team of British scientists this would be the culmination of a lifetime's endeavour - the flight alone, some 2 billion miles, would take a full seven years. This is the story of the space probe they built, the sacrifices they made and their hopes for the landing. Would their ambitions survive the descent into the unknown on Titan's surface?

We are in the grip of an allergy epidemic. 50 years ago one in 30 were affected, but in Britain today it is closer to one in three. Why this should be is one of modern medicine's greatest puzzles. In search of answers, Horizon travels round the globe, from the remotest inhabited island to the polluted centres of California and the UK. We meet sufferers and the scientists who have dedicated their lives trying to answer the mystery of why we are becoming allergic to our world.

Professor Robert Bartlett explores how the Normans developed from a band of marauding Vikings into the formidable warriors who conquered England in 1066. He tells how the Normans established their new province of Normandy -'land of the northmen' - in northern France. Under the leadership of Duke William, they conquered England. The Battle of Hastings marked the end of the Anglo-Saxon aristocracy and monarchy. The culture and politics of England would now be transformed by the Normans.

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.