In this instalment, entitled The Last Frontier, Sir David looks at how both traditional and modern people live in the harshest environment on Earth. I too will miss the penguins, but we need to move on. On the Siberian coast, folk still hunt walrus from open boats - it's dangerous work but a large walrus can feed the family for weeks. The Danish Armed Forces maintain their claim to Greenland's mineral wealth with an epic dog sled patrol, covering 2,000 miles. Scientists monitor the spectacular Northern Lights constantly as they can disrupt power supplies. At the South Pole there is a research base designed to withstand the world's most extreme winters, while the scientists explore life above and below the ice. Cut off from the outside world for six months, the base is totally self-sufficient - even boasting a greenhouse. And finally, the team travelled to Chukotka, in Russia, where people truly live on the edge.