Review: I Contain Multitudes by Ed Yong

Ed Yong has a great way of making you see the world differently. This book isn’t quite as good as An Immense World, but still super interesting. It focuses on the world of microbes, and after reading it, you’ll never think about bacteria, viruses, etc. the same way again.

The book’s strength is that it covers many different types of microbes, and their many roles in the world; this is also the book’s weakness, as not all parts are equally interesting, and a lot of the science on microbes is relatively new, so we just don’t know that much. As a result, some parts of the book feel like long lists of facts and theories.

Nevertheless, there are some really interesting and random insights within:

• We are never alone. Every animal is actually a collection of many different organisms living in symbiosis. You have more microbe cells in your body than your own cells. And most animals can’t live their lives without these microbes, so microbes make it tricky to even define a “self.” Hence the title of the book: I Contain Multitudes.

• Microbes vastly outnumber all other types of life on earth. They also vastly predate all other types of life on earth: for millions of years, it was just oceans of microbes. So it’s really their world; we just live in it.

• Multicellular life arose when one microbe permanently absorbed another, with the smaller one becoming mitochondria, and producing energy (ATP) to make multicellular life possible. As best as we can tell, this has only happened once in all of history, and all multicellular life descends from this.

• We tend to think of microbes as dirty and bad, but that really only applies to pathogens, which are a tiny, tiny percent of all microbes. The vast majority of microbes have no impact on human health, and many have a positive impact, either directly on us, or by supporting the ecosystem that we depend on.

• The goal should be not to kill all microbes, but to maintain the proper balance of microbes. If you kill off too many, there are huge negative effects, as you both eliminate beneficial microbes, and you create a situation where you may end up with a monoculture of solely harmful microbes (as there are no beneficial or neutral microbes to fight them off). This is a problem in some hospitals, where the conditions are, counterintuitively, too sterile. Allowing in some neutral microbes, perhaps by opening a window, would actually be better as it would help block out the harmful microbes.

• All animals pass microbes down to their young and family members. For example, you get your initial gut microbe from your mother’s milk; some animals secrete other substances for their young; some animals even eat each other’s feces to exchange microbes—that’s how important it is! But in the modern world, we may have gone too far in blocking this transfer: our houses are super sanitary; our water is chlorinated; we live with fewer animals than in the past; more babies are born by C section rather than vaginal birth (many microbes are passed from mother to child in a vaginal birth); we feed babies formula rather than milk; we use antibiotics, both on ourselves, and on the animals in our food supply (something all farmers know: cows fed antibiotics gain weight much faster); we don’t eat enough fiber; and so on. All of these changes mean that we have eliminated microbes that are beneficial to life, which may be part of the reason we are seeing health conditions in greater numbers than ever in the past, such as allergies, autoimmune diseases, etc.

• The microbes in our stomachs are critical in helping us digest food, and perhaps have an impact on obesity, diabetes, and possibly even mental health. The way the stomach keeps those microbes only in the stomach, and not other parts of the body where they may do damage, is multi-layered: the stomach lining itself is one layer; another layer is the mucus within it; another layer are the viruses that love to live in mucus and block other microbes from getting through; and then if something does get through, our immune system helps to protect us.

• We’ve developed probiotics, but many of them don’t really work: e.g., the microbes in many yogurts (e.g., Activia, Dannon) can’t actually colonize our stomachs, so they die off shortly after you eat them. The evidence for the health claims on some of these yogurts is so weak, the EU has rejected them, and won’t allow them on the labels.

Rating: 4 stars