A look at how a dung beetle standing on its head can roll a ball in a straight line; if egrets ever regret hanging out next to hungry alligators; and what ghostly creature was caught on camera 3000 feet below the ocean's surface.
The next instalment describes the move from water to land. The fish that did so may have been forced to because of drought, or chose to in search of food. Either way, they eventually evolved into amphibians. Such creatures needed two things: limbs for mobility and lungs to breathe. The coelacanth is shown as a fish with bony fins that could have developed into legs, and the lungfish is able to absorb gaseous oxygen. However, evidence of an animal that possessed both is presented in the 450 million-year-old fossilised remains of a fish called a eusthenopteron. Three groups of amphibians are explored.
Our planet was once populated by megafauna, big top-of-the-food-chain predators that played their part in balancing our ecosystems. When those megafauna disappear, the result is a "trophic cascade," where every part of the ecosystem reacts to the loss. How can we stay in balance? George Monbiot suggests rewilding: putting wolves, lions and other predators back on top -- with surprising results.
Horizon explores the secrets of what makes a long, healthy and happy life. It turns out that a time you can't remember - the nine months you spend in the womb - could have more lasting effects on you today than your lifestyle or genes. It is one of the most powerful and provocative new ideas in human science, and it was pioneered by a British scientist, Professor David Barker. His theory has inspired a field of study that is revealing how our time in the womb could affect your health, personality, and even the lives of your children.
For many endangered baby animals, the right zoo can mean hope for the entire species. Watch an endangered red panda cub get a warm welcome at Cornwall's Newquay Zoo, a rare baby macaque receive care from parents and keepers alike at the Dudley Zoological Gardens, and more.