Evolutionary thinking can also yield surprising medical therapies, the authors explain. Throughout much of our history, for example, humans coexisted with beneficial bacteria and intestinal worms. Reduced exposure to these bugs due to improved hygiene leaves many with immune systems that don't respond appropriately, scientists say. Research suggests we may be able to reduce our susceptibility to allergies, asthma, and many auto-immune diseases - from inflammatory bowel disease to multiple sclerosis - by giving patients "cocktails" of parasite eggs. "There are now 4000 people in a clinical trial to test the efficacy of worm eggs," said Stearns.