10% Human

10% Human: How Your Body's Microbes Hold the Key to Health and Happiness
© 2015 Alanna Collen
336 pages

Walt Whitman wasn't thinking of bacteria when he mused -- "I am large, I contain multitudes" -- but Alanna Collen could have gotten away with quoting him. She opens her book with the bombshell that ninenty percent of the 'cells' in our bodies are actually independent mcirobes, living their own little lives, and devotes the rest of it to exploring what effect that has on our health.  We are less discrete, self-contained individuals, and closer to mobile ecosystems,  in which microbes are an integral part and not just germy villains.  Microbes are not only essential parts of the human body -- slimy oil that keeps the body's engine running smoothly,  aiding in digestion and manufacturing essential elements like Vitamin B12. In some cases, like our own cells' mitochrondia, we've even adopted microbes into the family.  But there's more to the story of microbes and health, and Collen credits our overzealous germaphobia with many modern diseases.

Semmelweis did humanity and medicine a great favor when he realized the cause of childbed sickness was sloppy sanitation, but we may have taken his prescription too far in treating all microbes as 'germs' to be eradicated.  As mentioned, many are necessary to our bodily functions: babies receive helpful bacteria with their mothers' very milk.   Animal testing has indicated that bacterial species can have intense effects on their host: mice have changed personalities when their respective strains were switched, becoming more outgoing or more reserved; similar effects were observed in populations of lean and chubby mice.  That last is especially of note to an increasingly overweight global population, but there are no easy answers. (While some microbe species allow for the uber-efficient metabolization of food, stealthily increasing our caloric  intake, others produce byproducts that put fat cells on overdrive.)  The fact that our bodies contain many different types of bacteria is important, because they compete with one another. When we disrupt the balance of power with erratic courses of antibiotics, or abruptly and dramatically alter our diets,  nasty strains can dominate to our detriment. Collen attributes a number of 'western' or modern diseases to microbial havocincluding allergies and autism.  The section on autism has fantastic human interest: after one four-year old boy suddenly developed it after an ear inefection, his mother devoted herself to research, research the boy's sister continued decades lafter when she grew up and went to grad school.

10% Human is one of the more engaging pieces of biology writing I've ever read, and immensely importance from a personal and public health perspective.  Collen's' writing is very personable, never intimidating. She even sneaks in the tiniest bit of toilet humor when she refers to 'transpoosion', or transferring one person's fecal bacteria to another person's intestines to rebuild a ravaged microbial pool. (The  body has a bacterial backup in the appendix, but sometimes reinforcements are necessary.)  It should be obvious after a half-century of mass dieting and treadmill running than the simplistic calories in vs calories consumed model isn't adequate for explaining our weight woes, and here I suspect Collen will find a lot of appeal for people.  For me,  10% Human reminds me yet again of how we are not static creatures, built of DNA legos, but dynamic creatures -- constantly being remade, not only by our experience, but by the guests in our innards.

Related:

• Why We Get Sick: the New Science of Darwinian Medicine; Randolph M. Nesse, M.D; George C. Wiliams, Ph.D.
• Catching Fire: How Cooking Made us Human, Richard Wrangham
• "How Gut Bugs Make you Sick or Well", Time article from 2012 which mentions the mother-daughter research team.