It was during the Ice Age that humanity as we know it was forged. Two rival species competed until only one was left standing. Steve Backshall and Michaela Strachan travel the world to discover how Neanderthals and Homo sapiens survived at a time of brutal environmental change and uncover why we, Homo sapiens, survived while the Neanderthals were wiped off the face of the Earth. Steve heads to southern Germany, which is a hotbed of early human discoveries. In the freezing temperatures of the snow-lined valleys, Steve throws himself into Ice Age life, exploring how early humans evaded the mighty Ice Age predators such as the supersized cave bears and giant hyenas that stalked the freezing wastelands. In a battle against the elements and predators, Steve discovers how Neanderthals made fire in a surprisingly sophisticated way and crafted tools so sharp you could shave with them! Meanwhile, Michaela gets to grips with the differences between Neanderthals and Homo sapiens. At the prestigious Natural History Museum, she's able to see that Neanderthals were physically stronger than Homo sapiens and by looking at their skulls can see they even had bigger brains. So why then did we as a species survive and the Neanderthals did not? The answer could lie in how both species developed technology. Steve tests out the differences between how Neanderthals and Homo sapiens hunted mega-beasts like the woolly mammoth. He tries throwing Neanderthal spears, but discovers that Homo sapiens developed a better way to hunt. Meanwhile, Michaela uncovers how one invention, the humble sewing needle, gave Homo sapiens a huge advantage — why? But the biggest turning point in our species evolution came as the Ice Age thawed and a natural disaster loomed, one that threatened to wipe out the Neanderthals.

Deep within the Arctic Circle, Michaela is in freezing Svalbard solving the puzzle of why the Ice Age started in the first place. Meanwhile Steve is in the UK discovering which ice age mega beasts used the UK as their stomping ground. Joined by Professor Danielle Schreve, she introduces Steve to the bones of mammoth, arctic foxes and even a massive Ice Age hyena. But Danielle has an even bigger discovery, and only now is she prepared to let the cameras in! She and her team uncovered the remains of almost a dozen ice age creatures all found in the same small cave near Plymouth. What could have killed these ice age titans – did they all fall victim to natural disaster or was one apex predator responsible for their deaths? It's an Ice Age murder mystery for Steve to solve.

The most famous predator of the ice age was the sabre-toothed cat and Michaela discovers why this fearsome creature was such an effective hunter. But as she examines this beast's skull and giant fangs, she discovers it had one major weakness… Could this have been the reason it went extinct?

In Sweden Steve gets under the skin of the mammoth, by investigating its DNA. With the help of world leading geneticist Professor Love Dalén, Steve explores why this titan of the Ice Age died out. But it seems the mammoth may not be extinct for long… Steve discovers a revolutionary gene editing technique that could bring them back from the dead.