It's an encyclopedia about the human body, but it also talks about human evolution and history, and how the body works. It's hard to read because it keeps changing the theme.
Also, the images are old and the illustrations look outdated. When purchasing a DK book, be sure to check the publication year and choose a newer book if possible.
This book has very general content, so it would be better to read it in a specialized. For example, biology, anatomy, chemistry, genetics, neuroscience, immunology, endocrinology, pathology, biomechanics, psychology, nutrition, etc.