This Is Your Brain on Parasites

This is Your Brain on Parasites: How Tiny Creatures Manipulate Our Brains and Shape Society
© 2016 Kathleen McAuliffe
299 pages

Are you under the influence?  There’s a chance that you may be, even if you haven’t darkened the door of a bar in years. Our bodies are home to a multitude of microbes,  many of them allies of a sort:  in exchange for a moist roof over their heads, they help us digest food, or take up space that would otherwise be available to the disease-causing riff-raff.  Other,s however, are the riff-riff, and they can exert a bad influence on those who let them hang around.  By and large we’re familiar with bacteria that can cause disease, but there are microbes which have more subtle effects --  seemingly causing shifts in our mood, our metabolism, and our ability to think and process information. This is Your Brain on Parasites argues for a parasite-centered perspective on health and evolution,  told in four parts.    She opens by establishing the ubiquity and variety of microbes,  moves to demonstrating how some species can directly manipulate other species’ behavior,  argues that human beings’ mental/emotional state can be likewise influenced by microbes, and finally argues that much of human civilization is indirectly driven by parasites in that an obsession with cleanliness has driven us to create religions, laws, etc.

Whew! That’s a lot to take in in one book. The first two sections are paths well traveled, from 10% Human to Gut. The second section addresses an utterly fascinating aspect of nature, the ability of some species to manipulate others. The creatures documented here aren’t all microbes: parasitic wasps show up hijacking spiders and roaches and putting them to work, the first as a shelter-creator and the second as a beefsteak on the hoof.  The mechanisms for manipulation are not always known. Microbes aren’t comic book villains with glowing towers: they do their work with secretions of chemicals,  sometimes using our own bodies to produce it for them.  By subtle means can one parasite prompt grasshoppers to move en masse toward bodies of water, drowning themselves  Part of the difficulty of studying parasites is that their manipulation of one host is only one part of their life stage, and they usually have a series of hosts to go through to get back to where they can spawn. One parasite common to humans arrives  in the intestines, matures, works its way to the exit, raises hell to make us itchy, and then relies on a probing finger scratching the itch to carry their young out into the world to restart the cycle.  That’s more indirect manipulation, but the author also includes cases in which the presence of certain bacteria are strongly correlated with instances of depression, and others with dangerous, near-deadly behavior.

The last part, attributing everything from sanitation to religion to racism on human attempts to ward off parasites, is...interesting, but an example of how specialists in one field tend to view everything from their particular angle.   The fact that religious dietary laws often barred the very species which carry the most risk for internal parasites is insightful, but  human culture and evolution are rivers fed by many streams. Attributing the motherload to parasites, or cooking, or power, usually tells more about the author’s interests than the actual subject.  On the whole, however,  This is Your Brain on Parasites smartly marches through a lot of linked territory and makes itself of interest to general science readers.

Related:

• Parasite Rex, Carl Zimmer. A more in-depth treatment of parasites in general, and an inspiration for this book according to the author.  I read this back in 2008 but that was back in days when I posted one great big wall of text about every book I'd read in that week, and few of the 'reviews' were more than the same kind of abstract you'd find on an Amazon publisher' s description. 
• I Contain Multitudes, Gut, 10% Human.