Marlene Zuk has put together a fascinating and helpful book about our relationships with the biology that exists in our environment and how it can help us or hurt us. As a physician, I appreciate the detailed approach to the subject that some people may be shocked by. The relationship between our immune system and the biologic organisms in our environment is a fascinating and very timely subject. It is important to adapt to our environment including bacteria, bugs, and dirt. Our immune system needs to develop in a context of real life. Fortunately we can do that without catching too many diseases. One should not eat dirt ("Pica"), but some lightly cleaned fresh vegetables and some lactobacillous could be helpful. These suggestions are in-tune with part of this book. There are also excellent discussions about emerging threats in our environment, that are up-to-date, and important for us all. A great book!