Post Description

10. "Theme and Variations"
Broadcast 20 March 1979, this episode continues the study of mammals, and particularly those whose young gestate inside their bodies. Attenborough asks why these have become so varied and tries to discover the common theme that links them. Examples of primitive mammals that are still alive today include the treeshrew, the desman and the star-nosed mole. Insect eaters vary enormously from the aardvark, giant anteater and pangolin to those to which much of this programme is devoted: the bats, of which there are nearly 1,000 different species. These took to flying at night, and it?s possible that they evolved from treeshrews that jumped from tree to tree, in much the same way as a flying squirrel. Most bats use sonar to hunt and navigate, and ultrasound to communicate. However, some of their prey, such as the lacewing and tiger moth, have developed techniques to confuse and evade them. Aquatic mammals superseded sea-going dinosaurs such as the plesiosaur. The whales? immense size is related to the retention of body heat. The dinosaurs? growth was limited by the strength of their bones but the whales only rely on water to support their weight, and so have been able to grow into the world?s largest animals. Some of those shown include humpbacks, narwhals, killer whales and dolphins. The latter use echolocation in much the same way as bats, and Attenborough observes one finding objects in the water even after it has been blindfolded.