A little furry animal from the jungles of South East Asia, called a tree shrew, has attracted great interest from scientists because it shows how a great group of animals may have originated - the mammals. David Attenborough looks at some of the huge variety of mammals. Bats number over a thousand species, many hunt insects, some sip nectar, drink blood, and even catch fish. Contrast those which use sonar with the great whales that sing, the star-nosed mole and the giant anteater, and the potential variations become dramatically clear.