Humans don't rule the planet. Humans don't even rule their own bodies. During the past 20 years or so, it's become apparent that the guys in charge of everything are a nanometer across and run in packs, or perhaps more accurately, hang out in mobs. These gangs of microorganisms are together referred to as the microbiome, and we're just beginning to understand what these worlds within our world do to us and for us.
First, a little data, according to "Dirt Is Good," a recent book by Jack Gilbert, director of the University of Chicago Microbiome Center, and Rob Knight, director of the University of California Center for Microbiome Innovation, with science writer Sandra Blakeslee:
We're outnumbered. Microbes outweigh all visible plants and animals on earth by a factor of 100 million. The total number of bacteria alone is a 1 with 30 zeroes after it: a nonillion. For the total number of viruses, add two zeroes to those 30.
We're inexperienced. Microbes ran everything without an assist from humans, fish, ferns or even trilobites for about 3 billion of the last 4.5 billion years.
You're a minority even in your own skin. For every one of your cells, there are 1.3 microbial cells in your body. About 30 trillion cells are yours; another 40 trillion cells in your body are microbes. Together, those microbes weigh as much as your brain -- 3 pounds -- and have an astonishing influence on that organ, to say nothing of the sway they hold on your digestive tract, your urogenital system and your immune system.
At this point, it's an old joke but true: When the American poet Walt Whitman wrote, "I contain multitudes," he wasn't kidding. ("I Contain Multitudes" is also a 2016 book about the microbial world by science writer Ed Yong. )
While the existence of this microbial universe has never been a secret, until fairly recently, scientists had little access to its mysteries. Scientific scrutiny was limited to microbes that would grow in a laboratory, a remarkably teeny sample. What changed everything was the development of a technique to sequence microbial DNA directly from the environment. Pair that newfound ability with the rapid drop in the cost of genetic sequencing, and the field took off. "So what would have cost you $100 million 15 years ago costs you 100 bucks now, so there's a whole lot that we can do," Knight said in a phone interview.
For instance, science can now answer this riddle: Your baby hurls his pacifier onto the kitchen floor. To protect your infant's health, which is the best way to clean it?
A. Run the pacifier under hot water.
B. Pop the pacifier in your mouth, swish it around, then give it back to your pitcher-in-training.