Evolution

In the final episode, Attenborough explains why the islands have a greater number of species for their size than anywhere else on Earth. One factor is their isolation, which can even occur between different parts of an island. Volcán Wolf is cut off from the rest of Isabela Island by a barren lava flow. Aerial footage of giant tortoises which try to cross it show how they are baked alive by the tropical sun. Secondly, the deep geological forces which produced the islands are still at work. Volcanic activity, continental drift and erosion give each island its own character and each its own evolutionary community. An absence of large predators is a third factor. Galápagos hawks and Galápagos racers prey on young, weak or dying iguanas but this does not have much effect on the overall population. The inhabitants can reproduce freely and rapidly, thus accelerating evolutionary change. Attenborough uses the examples of Galápagos finches and lava lizards to show how variations in anatomy and behaviour on different islands can lead to speciation. He goes on to explain that scientists are now revealing how human beings are acting as an agent of evolutionary change. In the closing sequences, Attenborough is filmed with Lonesome George, the last surviving Pinta Island tortoise, and the pink iguana, a newly-discovered species found only on the slopes of Volcano Wolf.