One and a half million years ago, a new breed of ape-man walks the land. In southern Africa, Homo Ergaster has taken the next step to becoming human. They have long, modern looking noses, which cool air as they breathe. Their hairless bodies, with millions of tiny sweat glands, mean they don't pant anymore to control their temperature - they sweat. And, above all, they have big brains - nearly two-thirds the size of ours.

Horizon explores the strange and wonderful world of illusions – and reveals the tricks they play on our senses and why they fool us. We show how easy it is to trick your sense of taste by changing the colours of food and drink, explain how what you see can change what you hear, and see just how unreliable our sense of colour can be. But all this trickery has a serious purpose. It’s helping scientists to create a new understanding of how our senses work – not as individual senses, but connected together. It holds the intriguing possibility that one sense could be mapped into another.

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. He has his mind scrambled by a cutting-edge experiment in anaesthesia. After, Marcus is given an out-of-body experience in a bid to locate his true self.

Go with us on a mathematical mystery tour, a provocative exploration of math's astonishing power across the centuries. We discover math's signature in the swirl of a nautilus shell, the whirlpool of a galaxy, and the spiral in the center of a sunflower. Math was essential to everything from the first wireless radio transmissions to the successful landing of rovers on Mars. But where does math get its power?" Astrophysicist and writer Mario Livio, along with a colorful cast of mathematicians, physicists, and engineers, follow math from Pythagoras to Einstein and beyond, all leading to the ultimate riddle: Is math an invention or a discovery? Humankind's clever trick, or the language of the universe? Whether we think we're good with numbers or not, we all use math in our daily lives. The Great Math Mystery sheds fascinating light on how math works in our brains and ponders the ultimate mystery of why it works so well when decoding the universe.

We now know that the brain - the organ that more than any other makes us human - is one of the wonders of the universe, and yet until the 17th century it was barely studied. The twin sciences of brain anatomy and psychology have offered different visions of who we are. Now these sciences are coming together and in the process have revealed some surprising and uncomfortable truths about what really shapes our thoughts, feelings and desires. And the search to understand how our brains work has also revealed that we are all - whether we realise it or not - carrying out science from the moment we are born.

Dr Aleks Krotoski concludes her investigation of how the World Wide Web is transforming almost every aspect of our lives. Joined by Facebook founder Mark Zuckerberg, Bill Gates, Al Gore and the neuroscientist Susan Greenfield, Aleks examines the popularity of social networks such as Facebook and asks how they are changing our relationships. And, in a ground-breaking test at University College London, Aleks investigates how the Web may be distracting and overloading our brains.