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.