Rob Dunn is a microbiologist determined to make the invisible world of microscopic organisms present in our everyday lives. In this book he focuses on the human body and its evolution from wild animal to modern species. He points out, for example, that our appendix, long thought to be vestigial, actually served a purpose as an island for productive bacteria to grow. When vicious bacteria, like cholera, wipe out the productive flora in our gut, our large intestines could be repopulated with good bacteria from our appendix. In another example, Dunn points to new research suggesting that our immune systems evolved in cooperation with parasitic worms and when antibiotics and modern hygiene removed these from our digestive tracts, autoimmune disorders blossomed. Lupus, allergies, asthma, Crohn’s and similar diseases are plentiful in the world’s most developed countries and virtually nonexistent in countries where parasites persist. There is some evidence that infecting sick patients with parasitic worms can bring relief. Dunn sometimes gets so excited by new discoveries that he effervesces for pages when he could just get to the punchline.