This book provides the hard facts on human similarities and differences, their causes and effects on people. It covers the whole range from normal to extreme human types, and presents — for the first time — much of the author's 25 years of original research on the subject. It can also act as a family medical guide to aspects of human function, structure and disease. It covers many human topics in a humane and understandable fashion, providing much material for information and discussion. It can be used as a handbook or textbook on human diversity, but is mainly popular science for the general public.