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Theme and Variation • 1979 • episode "10/13" Life on Earth

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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 its possible that they evolved from treeshrews that jumped from tree to tree, in much the same way as a flying squirrel.

Life on Earth • 1979 • 7 episodes •

Conquest of the Waters

This programme looks at the evolution of fish. They have developed a multitude of shapes, sizes and methods of propulsion and navigation. The sea squirt, the lancelet and the lamprey are given as examples of the earliest, simplest types. Then, about 400 million years ago, the first back-boned fish appeared. The Kimberley Ranges of Western Australia are, in fact, the remnants of a coral reef and the ancient seabed. There, Attenborough discovers fossils of the earliest fish to have developed jaws. These evolved into two shapes of creature with cartilaginous skeletons: wide ones (like rays and skates) and long ones (like sharks).

1979 • Nature

Lords of the Air

This programme focuses on birds. The feather is key to everything that is crucial about a bird: it is both its aerofoil and its insulator. The earliest feathers were found on a fossilised Archaeopteryx skeleton in Bavaria. However, it had claws on its wings and there is only one species alive today that does so: the hoatzin, whose chicks possess them for about a week or so. Nevertheless, it serves to illustrate the probable movement of its ancestor. It may have taken to the trees to avoid predators, and over time, its bony, reptilian tail was replaced by feathers and its heavy jaw evolved into a keratin beak.

1979 • Nature

Rise of the Mammals

This instalment is the first of several to concentrate on mammals. The platypus and the echidna are the only mammals that lay eggs (in much the same manner of reptiles), and it is from such animals that others in the group evolved. Since mammals have warm blood and most have dense fur, they can hunt at night when temperatures drop. It is for this reason that they became more successful than their reptile ancestors, who needed to heat themselves externally. Much of the programme is devoted to marsupials (whose young are partially formed at birth) of which fossils have been found in the Americas dating back 60 million years.

1979 • Nature

Theme and Variation

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 its possible that they evolved from treeshrews that jumped from tree to tree, in much the same way as a flying squirrel.

1979 • Nature

Hunters and Hunted

This programme surveys mammal herbivores and their predators. The herbivores began to populate the forests when the dinosaurs disappeared, and many took to gathering food at night. To prepare for winter, some store it in vast quantities, some hibernate and others make do as best they can. However, the carnivores joined them, and when a drying climate triggered the spread of grass, they followed their prey out on to the plains. Grass is not easily digestible and most animals that eat it have to regurgitate it and chew the cud. Out in the open, the leaf-eaters had to develop means of protection.

1979 • Nature

Life in the Trees

The penultimate instalment investigates the primates, whose defining characteristics are forward-facing eyes for judging distance, and gripping hands with which to grasp branches, manipulate food and groom one another. The programme begins in Madagascar, home to the lemurs, of which there are some 20 different types. Two examples are the sifaka, which is a specialised jumper, and the indri, which has a well-developed voice. Away from Madagascar, the only lemur relatives to have survived are nocturnal, such as the bushbaby, the potto and the loris. The others were supplanted by the monkeys and a primitive species that still exists is the smallest, the marmoset. However, Attenborough selects the squirrel monkey as being typical of the group. Howler monkeys demonstrate why they are so named their chorus is said to the loudest of any mammal and their prehensile tails illustrate their agility.

1979 • Nature

Compulsive Communicators

The final episode deals with the evolution of the most widespread and dominant species on Earth: humans. The story begins in Africa, where, some 10 million years ago, apes descended from the trees and ventured out into the open grasslands in search of food. They slowly adapted to the habitat and grew in size. Their acute sense of vision led to them standing erect to spot predators, leaving their hands free to bear weapons. In addition, the primitive apemen also had stones that were chipped into cutting tools. Slowly, they grew taller and more upright, and their stone implements became ever more elaborate.

1979 • Nature

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Theme and Variation

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 its possible that they evolved from treeshrews that jumped from tree to tree, in much the same way as a flying squirrel.

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