Intelligence and adaptability allow primates to tackle the many challenges of life, and this is what makes our closest relatives so successful. This resourcefulness has enabled primates to conquer an incredible diversity of habitat. Hamadryas baboons live on the open plains of Ethiopia in groups up to 400 strong. Strength in numbers gives them some protection from potential predators. But, should their path cross with other baboon troops, it can lead to all-out battle, as males try to steal females from one another, and even settle old scores. Japanese macaques are the most northerly-dwelling primates and they experience completely different challenges. Some beat the freezing conditions by having access to a thermal spa in the middle of winter. But this privilege is only for those born of the right female bloodline. For western lowland gorillas, it's the male silverback that leads his family group in the rich forests of the Congo basin. He advertises his status to all with a powerful chest-beating display. Most primates are forest dwellers, and one of the strangest is the tarsier – the only purely carnivorous primate. As it hunts for insects the tarsier leaps from tree to tree in the dead of night, using its huge forward-facing eyes to safely judge each jump. Good communication is essential for success in primate society.

Sagan discusses the story of the Heike crab and artificial selection of crabs resembling samurai warriors, as an opening into a larger discussion of evolution through natural selection (and the pitfalls of intelligent design). Among the topics are the development of life on the Cosmic Calendar and the Cambrian explosion; the function of DNA in growth; genetic replication, repairs, and mutation; the common biochemistry of terrestrial organisms; the creation of the molecules of life in the Miller-Urey experiment; and speculation on alien life (such as life in Jupiter's clouds). In the Cosmos Update ten years later, Sagan remarks on RNA also controlling chemical reactions and reproducing itself and the different roles of comets (potentially carrying organic molecules or causing the Cretaceous–Paleogene extinction event).

In this programme, Mary descends into the city streets to discover the dirt, crime, sex and slum conditions in the world's first high-rise city. This Rome is not the marble Rome we know, but a vast, messy metropolis with little urban planning, where most Romans lived in high-rise apartment blocks with little space, light, or even sanitation. Forced outdoors into the city streets, she reveals where they went to hang out, get drunk, have sex and get clean. She looks at the Forum as a place of gamblers, dentists and thieves, and she explores the lustiness of Roman bar life and jokes. Finally, exploring law and order from the bottom up, Mary examines how this city really worked. She meets Ancarenus Nothus, an apartment dweller who lived in fear of the rent collector; Notorious Primus, who wrote about his three great pleasures in life - baths, wine and sex; and Unlucky Doris, a seven-year-old girl killed in one of Rome's many fires.

Evolution tells us that all life exists for only one purpose: to reproduce. But is that all there is? How could such a simple imperative lead us to create great art and civilizations? A new theory suggests that instead of passing on genes, our ultimate purpose is to process and pass on information. We are the universe figuring itself out. Scientists dig deep into DNA, chemistry, technology and engineering to find the meaning of life. One thing is certain: living is easier if you find a reason for living.

Beneath Jupiter's swirling clouds lie our solar system's deepest secrets: from its violent youth, through the birth of life to the death of the sun. Now, scientists are unlocking these secrets and discovering that every living thing exists thanks to Jupiter.

(Click CC for English subtitles) Four Finnish cave divers face their worst nightmare when two of their friends drown deep inside an underwater cave in Norway. When the official recovery operation is called off by the Norwegian and British authorities after being deemed too risky, the friends set out on a secret mission to retrieve the bodies themselves. "Diving into the Unknown" isn’t just the dramatic story of a life-threatening mission. It is also a story about unconditional friendship that truly runs deep. While each member of the team has years of experience exploring dangerous deep-sea caves, together they are about to face the biggest challenge of their lives. To make it out alive, they will need to be able to rely on each other every second of the way. And the physical demands of this operation will pale in comparison to the psychological toll it will take on everyone involved. With footage from the actual accident and multiple cameras both above water and deep below the surface, this film follows the breathtaking recovery mission from beginning to end.