The Life of Mammals

David Attenborough meets the tree dwellers - those mammals that have adapted to a life at height. Some, like meerkats, might hardly seem to qualify but they do regularly climb small trees to scout for danger. Others, like gibbons, live 100 feet or more above the forest floor and never descend to the ground.

One third of the world's surface is still covered by forest of one kind or another and mammals from a diverse range of groups have exploited them all.

Climbing requires some very specialised adaptations. Hyrax have moist, rubbery feet to help them negotiate slender branches, sun bears rely on sharp claws and strong forearms, coatis go one step further with sharp claws and a long tail for balance. And, when it comes to tails, there's another very effective design. Tamanduas, arboreal anteaters, have gripping tails, which leaves their hands free to break into termite mounds.

But climbing into a tree is just the start. The real challenge is how to move between trees. Grey squirrels cope with small gaps by jumping, a technique favoured by many primates as well as bush babies and lemurs. The latter can leap thirty feet in one go but there are other tree dwellers that can travel further than that. By stretching out a membrane between front and back legs, flying squirrels can glide three times that distance, while fruit bats, along with their insect-eating cousins, are the only mammal to have developed powered flight and their strong wings enable them to fly as much as 30 miles in a night in their search for fruiting trees.

Life in the Trees is full of strange and unfamiliar animals, such as the Indian slender loris and the fossa, Madagascar's largest arboreal predator, both filmed for the first time in the wild. In this programme, David gets close to many of them, and for some this meant climbing high into the canopy himself.

In the penultimate episode, David Attenborough looks at monkeys. This group started its life in the tree-tops and this is where we join the capuchin, whose acute vision and lively intelligence helps them findclams in the mangrove swamps of Costa Rica and crack them open on tree-anvils. The swamps are also full of biting insects, but the monkeys rub themselves with a special plant that repels them.

In the forests of South America, we see how different species of monkey can live alongside one another by having slightly different diets. The saki is a living nut-cracker, the spider monkey uses its tail to reach the ripest fruit and the pygmy marmoset is so small that even the outermost twigs of the canopy can support its weight as it stalks insects. David even meets an owl monkey, a shy and mysterious creature with huge eyes that feeds at night to avoid competition with the others.

Hanging from a rope high in the forest canopy of Venezuela, David watches the stunning red howler monkey as it uses excellent colour vision to pick the best leaves. Although colour vision evolved to detect leaves and ripe fruit, it allowed the monkeys to become the most colourful of all mammals. The scarlet face of a uakari is dazzling, the long moustache of the emperor tamarin is striking even from a distance, but the most beautiful colours are found on the guenons of west Africa that use intricate patterns on their faces to send social messages.

These guenons are under constant threat from eagles, leopards and chimps, but different types of guenon join forces with other monkeys. They travel together in an extraordinary anti-predator alliance based on shared vigilance and a remarkable degree of vocal communication.

But the most complex relationships to be found in the monkeys are between animals living in the same group. And the larger the group, the more individuals with good social skills will thrive. In Sri Lanka, we watch male toque macaques battle for mates and see how brain can triumph over brawn.

Ten million years ago, a change in climate allowed one group of African monkeys to move down from the trees and on to the grasslands. But living on the ground brought an increased risk from predators, forcing baboons to live in even larger groups - and this put an even greater emphasis on social skills. Life on the ground also opened up new hunting opportunities - the hapless flamingos of Kenya are now on the menu.

Several miles above the savannah, in the highlands of Ethiopia, we meet the monkeys that live in the largest groups of all - geladas. Groups of 800 drift across the high plains like herds of wildebeest. It is hard for so many animals to stay in contact by grooming, so these monkeys have another way of communicating - they chatter to each other using the most complex sounds made by any mammal yet studied, except for ourselves. So while monkeys in the treetops have rich and varied social lives, it is those that came down to the ground that developed the most complex and communicative societies of all - a fact not without significance for our own ancestry.

David Attenborough concludes his documentary series with a programme about our closest animal relatives, the intelligent great apes, and finds out how their large brains enabled one of their kind, an upright ape, to go on to dominate the planet. David travels to the forests of Borneo to meet a remarkable orangutan with a passion for DIY and a talent for rowing boats. He shifts continent to Africa and takes part in a special nut-cracking lesson with a group of chimps learning survival skills. He discovers how food - and the ways apes find it - has been key to the evolution of our large brains.

Filmed for the first time, the chimps of Ngogo hunt down monkeys to supplement their vegetarian diet with meat. Our ancestors must have also hunted for meat, but with one crucial difference - they did so on two feet. David meets an extraordinary group of wading chimps that give us a unique window into our past, the moment when we took a step away from being apes and a step towards humanity. As soon as they stood upright, humans began to manipulate their environment, transforming the very surface of the planet by domesticating plants and animals. This most successful of all mammals has been able to increase the supply of food beyond that which occurred naturally. As a result the number of human beings could increase. David travels to the ruins of the capital of the Maya people to trace the rise and fall of an entire human civilisation. The temples of Tikal used to be the highest buildings in the Americas until the skyscrapers of New York were built. So why did the Maya civilisation collapse? Will modern city-dwellers suffer a similar fate?