In the final three episodes of the series, Chris Packham follows three extraordinary evolutionary journeys to discover how the relentless demands of survival transformed simple early animals into some of the most remarkable creatures alive today. In Borneo, the voracious appetite of the bat leads back more than half a billion years to the origins of the through-gut, the first anus, heads and jaws, revealing how the need to find and consume food helped reshape animal life and ultimately produced the bat’s extraordinary powers of hearing. In the Bahamas, the intelligence of dolphins opens an even deeper story: from ancient cells able to sense light to the evolution of eyes, complex brains, sophisticated senses and the remarkable minds of modern dolphins. The journey culminates with one of nature’s supreme athletes. Tracing the horse’s ancestry through hundreds of millions of years, Packham reveals how primitive muscle cells evolved into increasingly powerful systems for movement, how beating hearts supplied those muscles with oxygen, and how limbs became ever more effective tools for locomotion. Slithering, swimming, walking and running eventually converge in an animal built for extraordinary speed and endurance. Together, these final episodes reveal a breathtaking truth: hunger, perception and movement were not merely necessities of survival—they were powerful evolutionary forces that helped create the astonishing complexity of animal life.
The fifth programme explores the alliances formed between the animal and plant worlds. Attenborough dives into Australia's Great Barrier Reef and contrasts the nocturnal feeding of coral, on microscopic creatures, with its daytime diet of algae. Some acacias are protected by ants, which will defend their refuge from any predator. Besides accommodation, the guards are rewarded with nectar and, from certain species, protein for their larvae as well. Fungi feed on plants but can also provide essential nutriment to saplings (Mycorrhiza). The connection is never broken throughout a tree's life and a quarter of the sugars and starches produced in its leaves is channelled back to its fungal partners. Meanwhile, fungi that feed on dead wood leave a hollow trunk, which also benefits the tree. Orchids enjoy a similar affiliation. Lichens are the product of a relationship between fungi and a photosynthetic associate, usually algae. They are extremely slow-growing, and a graveyard is the perfect location to discover their exact longevity. Mistletoe is a hemiparasite that obtains its moisture from a host tree, while using own leaves to manufacture food. Its seeds are deposited on another by the mistletoe tyrannulet, following digestion of the fruit. The dodder (Cuscuta) is also parasitic, generally favouring nettles, and siphons its nourishment through periodic 'plugs' along its stem. The rafflesia has no stem or leaves and only emerges from its host in order to bloom — and it produces the largest single flower: one metre across.
The episode is a journey through the human gut and the process of turning food into energy to keep the body going. Humans have turned eating into culture, a way to celebrate our roots, to bring us together. But food is really just one thing: Fuel. It's where you get the power to live your life. Even when you're sitting completely still, your body needs a lot of energy to stay on. But nowhere is the need for fuel more apparent than when you push yourself to the absolute limit. And the microbiome, the bacteria living in our gut, plays a great role in all this.
The journey culminates with one of nature’s supreme athletes. Tracing the horse’s ancestry through hundreds of millions of years, Packham reveals how primitive muscle cells evolved into increasingly powerful systems for movement, how beating hearts supplied those muscles with oxygen, and how limbs became ever more effective tools for locomotion. Slithering, swimming, walking and running eventually converge in an animal built for extraordinary speed and endurance. Together, these final episodes reveal a breathtaking truth: hunger, perception and movement were not merely necessities of survival—they were powerful evolutionary forces that helped create the astonishing complexity of animal life.