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I Contain Multitudes: The Microbes Within Us and a Grander View of Life is an in-depth introduction to the microbiome and how it interacts with humans. Ed Yong, who has written for many publications such as The New Yorker, Wired, The New York Times, and Nature wrote this book. It was originally published in 2016; this guide is based on the 2018 paperback edition.

Yong talks about how microbes affect humans. He explains that it’s been difficult to study them because they’re so small and hard to see, but he describes the history of microbiology, starting with Anton van Leeuwenhoek, a Dutch lens maker who discovered that there were animalcules everywhere. Yong goes on to discuss the difficulty in replicating his findings, as no one else could see what he saw.

Two hundred years ago, scientists thought of microbes as a disease-causing agent. They were primarily focused on the role of bacteria in causing illnesses and not much else. Then Martinus Beijerinck discovered that certain types of bacteria could be useful to humans by turning nitrogen from the air into ammonia for plants to use. This discovery led people to discuss “good germs” that were beneficial to us. Scientists began looking at how organisms coexist with each other, which is known as symbiosis.

Humans and microbes have evolved together because we provide them with homes, and they help us. The author provides examples of this symbiotic relationship throughout the book to show how it affects our evolution.

In the last chapter, Yong talks about probiotics and fecal transplants. He mentions that there is not enough evidence to support their use, but he also explains how they work (probiotics are used to treat diarrhea). He notes that we need more research on bacteria because it can change our lives in many ways. We will likely see a lot of new developments in medicine as well as architecture and design because of these discoveries.

Prologue: “A Trip to the Zoo”

The microbiome refers to the collection of microscopic organisms that live within your body. The interactions between these microbes and you are complicated, and there’s a lot we don’t know about them yet.

Microbes are so important that we cannot understand the lives of creatures without understanding how microbes help them. We also can’t truly understand microbiomes without knowing about other species’ interactions with their microbiomes. The link between bacteria and ourselves offers us a vast amount of knowledge about the world around us.

We are never really alone. There are many organisms that live in our bodies and help us digest food, fight off infections, etc. However, there is still much that we don’t know about these organisms. Walt Whitman said “I contain multitudes” to describe this phenomenon

Chapter 1: “Living Islands”

To understand our microbiome, we must look at the planet’s history and think of it as a year. In this analogy, humans have only existed for 30 seconds in that entire year. Microbes have been around since March and had the rest of the world to themselves until October.

Bacteria have been around for a long time. They’ve changed the way that planet Earth functions and they’re still changing it today. Bacteria are everywhere, but we can’t see them because they’re so small. In fact, bacteria helped to create life on Earth and we evolved from bacteria.

Archaea and bacteria coexisted before eukaryotes were in the world. Archaea are more difficult to study, but we know that they exist in extreme environments. A bacterium merged with an archaeon, which trapped the bacterium within it. This merge eventually led to eukaryotes, multicellular organisms, because of evolutionary happenstance. The bacteria became mitochondria inside cells (which provided energy) as a result of this merger. We can even see remnants of these two groups today through our genes, just like all our cells have mitochondria (because of this merge). The addition of mitochondria allowed for bigger and more complex cells due to the additional energy we could put into growth.