Why do humans differ from other primates? What do those differences tell us about human evolution? Elaine Morgan gives a revolutionary hypothesis that explains our anatomic anomalies--why we walk on two legs, why we are covered in fat, why we can control our rate of breathing. The answers point to one conclusion: millions of years ago our ancestors were trapped in a semi-aquatic environment. In presenting her case Elaine Morgan forces scientists to question accepted theories of human evolution, while expressing complex ideas for the general reader in a clear and accessible style. A documentary by Sir David Attenborough, The Waterside Ape, is based on Morgan's Aquatic Ape Hypothesis.