Lewis Thomas, the noted physician and essayist, mused openly on the allergic tendency of our species. He found the condition without teleological merit, and declared it a "mistake." Now two books—Mark Jackson’s Allergy: The History if a Modern Malady and Gregg Mitman’s Breathing Space, How Allergies Shape Our Lives and Landscapes—are available for those who wish to delve further into this "mistake" that affects 50 million Americans.