I Contain Multitudes.

You are currently covered in bugs.

That’s the fact that drives Ed Yong’s book I Contain Multitudes: The Microbes Within Us and a Grander View of Life, his highly acclaimed 2016 book about the microbiome, a relative neologism that refers to the interconnected world of microorganisms that exist in, on, and around all other life on earth. Without these bugs, we almost certainly wouldn’t exist, and the best estimates Yong has have bacteria and other microbes in and on our bodies outnumbering the cells of our actual bodies by a margin slighter over 1:1. You do not just contain multitudes, Yong quips (borrowing a line from Walt Whitman), but you are multitudes.

Yong spends as much time dispelling myths as he does explaining the new science of the microbiome because everyone who reads this has probably grown up believing one of two things about bacteria and other microbes: They’re dirty and bad and cause illness and death; or, some bacteria are good and we want lots of them but not the bad ones. Yong says neither is accurate; there aren’t “good” or “bad” microbes per se, but that the effect a microbe can have depends entirely on where it lives and thus what it’s able to do.

Microbes make the complexity of life on earth possible, sometimes serving as the difference between life and not-life, as in creatures that live in inhospitable, lightless environments at the bottom of the ocean near steam vents that bring geothermal heat out into the water. Scientists discovered creatures there that seemed to have no business existing in the first place, such as a worm that had no mouth or digestive tract. It turned out that the worm in question plays host to bacteria that provide it with all of the energy the worm needs by converting sulfur compounds found in that dark environment into chemicals the worms can use.

He also explains how evolution works differently – and apparently faster – in bacteria than it does in multicellular organisms, thanks to something called HGT, Horizontal Gene Transfer. (As opposed to, say, the Mariners moving Segura to second base if Cano is hurt; that would be a Horizontal Jean Transfer.) Bacteria have the ability to swap genes with other bacteria in their environment, meaning they can alter their genome on the fly while still alive, as opposed to humans, who are stuck with the genes that brought us to the dance.

Perhaps most relevant to the lay reader are the two chapters near the end of the book where Yong talks about how probiotics don’t work and how we might use bacteria, including their HGT superpowers, to fight diseases like dengue and Zika. Probiotic products are all the rage now, but there’s no evidence that swallowing these bacteria – which appear in tiny amounts even in products like yogurt – alters your microbiome in any way. Your gut flora are largely a function of what you were born with, meaning in turn what you got from your mother in birth (vaginal delivery exposes the infant to the bacteria in the mucosal lining) or via breast feeding (which contains more bugs plus compounds that encourage the growth of helpful bacteria in the cut), and what you eat now (more fiber, please). So skip the kombucha and eat more plants.

Mosquitoes that spread disease often do so with the help of bacteria they host, but there’s an effort underway in Australia – a country far less hostile to science than the United States is – to release mosquitoes of the same species that carries viruses like dengue or chikungunya, A. Aegyptes, that have been infected with a Wolbachia bacterium that renders the critters immune to the viruses. These mosquitoes would then move into the environment, mate with other mosquitoes, and thus spread the bacterial ‘infection’ through the population, thus dramatically reducing the number of bugs flying around with the disease in the first place. A separate but related endeavor aims to do the same with the mosquitoes that carry the parasite that causes malaria in people, a disease that has proven particularly obstinate to the development of a vaccine (in part because it’s neither viral nor bacterial).

Yong’s book seems comprehensive, although I came into it knowing extremely little about the subject. He gets into fecal transplants, including why they’ve helped people with deadly C. dif infections where traditional treatments failed. He discusses antibiotic resistance, of course. He provides copious examples of symbiosis and dysbiosis in the wild, and how many species, including animals, deprived of their normal microbiomes fail to thrive. And he gets into how climate change is altering microbiomes worldwide, leading to mass deaths on coral reefs and the spread of a fungus (also highlighted in Elizabeth Kolbert’s The Sixth Extinction, the most recent winner of the Pulitzer Prize for Non-Fiction) that has already wiped out numerous species of tropical frogs.

Most important, however, is that Yong keeps this all so accessible. I find the subject interesting anyway, but his prose is readable and his stories quick and quirky enough that the audiobook held my attention throughout, including during some rather dreadful trips between spring training sites in Florida. Granted, it might make you think very differently about shaking hands or touching various surfaces, but I Contain Multitudes might also encourage you to eat better, get a dog, and throw out all your triclosan, while giving you a new appreciation for germs.