During 1964-1969 both sides now plan to put a man on the Moon - while the Soviets struggle, the Americans pull ahead in the space race with Project Gemini, but then suffer a disaster with the Apollo 1 fire. The Soviet space programme suffers its own blows: Sergei Korolev dies when his heart fails during an operation, Soyuz 1 crashes and kills cosmonaut Vladimir Komarov, and their planned moon rocket, the N-1 rocket, fails to successfully launch. In America, von Braun has difficulties with the Saturn V, but they are overcome, and the rocket successfully launches the first manned lunar mission, Apollo 8, and the first manned lunar landing, Apollo 11.

Northern Africa is home to the greatest desert on Earth, the Sahara. On the fringes, huge zebras battle over dwindling resources and naked mole rats avoid the heat by living a bizarre underground existence. Within the desert, where the sand dunes 'sing', camels seek out water with the help of their herders and tiny swallows navigate across thousands of square miles to find a solitary oasis. This is a story of an apocalypse and how, when nature is overrun, some are forced to flee, some endure, but a few seize the opportunity to establish a new order.

In the third programme of the series, Aleks gives the lowdown on how, for better and for worse, commerce has colonized the web - and reveals how web users are paying for what appear to be 'free' sites and services in hidden ways. Joined by some of the most influential business leaders of today's web, including Eric Schmidt (CEO of Google), Chad Hurley (CEO of YouTube), Bill Gates, Martha Lane Fox and Reed Hastings (CEO of Netflix), Aleks traces how business, with varying degrees of success, has attempted to make money on the web. She tells the inside story of the gold rush years of the dotcom bubble and reveals how retailers such as Amazon learned the lessons. She also charts how, out of the ashes, Google forged the business model that has come to dominate today's web, offering a plethora of highly attractive, overtly free web services, including search, maps and video, that are in fact funded through a sophisticated and highly lucrative advertising system which trades on what we users look for. Aleks explores how web advertising is evolving further to become more targeted and relevant to individual consumers. Recommendation engines, pioneered by retailers such as Amazon, are also breaking down the barriers between commerce and consumer by marketing future purchases to us based on our previous choices. On the surface, the web appears to have brought about a revolution in convenience. But, as companies start to build up databases on our online habits and preferences, Aleks questions what this may mean for our notions of privacy and personal space in the 21st century

The tour was designed by Willie Williams, who has worked on every U2 tour since 1982. Williams had been toying with ideas for 360-degree stadium staging for U2 for a number of years, and presented sketches of a four-legged design to the group near the end of their Vertigo Tour in 2006. The inspiration for the 'spaceship-on-four-legs' design, nicknamed 'the Claw', came from the landmark Theme Building at Los Angeles International Airport.

The second programme deals with the mechanics of flight. Getting into the air is by far the most exhausting of a bird's activities, and Sir Attenborough observes shearwaters in Japan that have taken to climbing trees to give them a good jumping-off point. The albatross is so large that it can only launch itself after a run-up to create a flow of air over its wings. A combination of aerodynamics and upward air currents (or thermals), together with the act of flapping or gliding is what keeps a bird aloft. Landing requires less energy but a greater degree of skill, particularly for a big bird, such as a swan. Weight is kept to a minimum by having a beak made of keratin instead of bone, a light frame, and a coat of feathers, which is maintained fastidiously. The peregrine falcon holds the record for being fastest in the air, diving at speeds of over 300 km/h. Conversely, the barn owl owes its predatory success to flying slowly, while the kestrel spots its quarry by hovering. However, the true specialists in this regard are the hummingbirds, whose wings beat at the rate of 25 times a second. The habits of migratory birds are explored. After stocking up with food during the brief summer of the north, such species will set off on huge journeys southwards. Some, such as snow geese, travel continuously, using both the stars and the sun for navigation. They are contrasted with hawks and vultures, which glide overland on warm air, and therefore have to stop overnight.

Survival of the fittest: Raw competition? Intense cooperation? Both are essential. Interactions between and within species are among the most powerful evolutionary forces on Earth, and understanding them may be a key to our own survival.