This book is also available under the title "Why we get sick". I, like Richard Dawkins who greatly praises this book, get sick of publishers mucking around with titles. The book's reviews under the other title should tell you all that you need to know.Why We Get Sick
If you are curious as to why things happen, as well as just how, then you will be likely to find this book a very interesting and informative read. It proposes evolutionary explanations for why we get sick and why we get the symptoms we do - including how some symptoms that cause us discomfort can also have beneficial/protective purpose.
The book is also well written (so its entertaining rather than being dull to read) and you don't need to have a scientific background to enjoy it. Apparently its also under the title of 'Why we get sick', so its worth looking at those reviews too.