"Engrossing ... [An] expedition through the hidden and sometimes horrifying microbial domain." -Wall Street Journal "Fascinating-and full of the kind of factoids you can't wait to share." -Scientific American Parasites can live only inside another animal and, as Kathleen McAuliffe reveals, these tiny organisms have many evolutionary motives for manipulating the behavior of their hosts. With astonishing precision, parasites can coax rats to approach cats, spiders to transform the patterns of their webs, and fish to draw the attention of birds that then swoop down to feast on them. We humans are hardly immune to their influence. Organisms we pick up from our own pets are strongly suspected of changing our personality traits and contributing to recklessness and impulsivity-even suicide. Germs that cause colds and the flu may alter our behavior even before symptoms become apparent. Parasites influence our species on the cultural level, too. Drawing on a huge body of research, McAuliffe argues that our dread of contamination is an evolved defense against parasites. The horror and revulsion we are programmed to feel when we come in contact with people who appear diseased or dirty helped pave the way for civilization, but may also be the basis for major divisions in societies that persist to this day. This Is Your Brain on Parasites is both a journey into cutting-edge science and a revelatory examination of what it means to be human. "If you've ever doubted the power of microbes to shape society and offer us a grander view of life, read on and find yourself duly impressed." -Heather Havrilesky, Bookforum