A Short History of Nearly Everything: Chapter 20 Summary & Analysis

There’s no point hiding from bacteria because they’re perpetually “on and around you”: healthy people have about a trillion bacteria living on their skin alone that eat dead skin, oils, and minerals from our bodies. There are trillions more in our gut and nasal passages, on our eyes, and in our teeth. We think antibiotics and disinfectants have all but rid the world of bacteria, but Bryson says that in actuality, Earth is the bacteria’s planet—they were here before us, and they’ll be here long after us. We’re alive because of bacteria, which perform all the necessary functions to keep us and Earth running—including converting nitrogen into amino acids, making waste rot, converting food into sugars, and keeping our atmosphere oxygenated.

Bacteria reproduce much more quickly than humans—in a matter of minutes. When bacteria reproduce, about one in a million of their offspring is a mutant. Usually, mutants don’t survive, but sometimes the mutant has an accidental advantage such as the ability to resist antibiotics. Bacteria share these advantages easily and rapidly because they share a single gene pool. All they need to survive is moisture—and they’re everywhere, from the bottom of the Mariana Trench to deep inside Earth’s interior. Some are even immune to radioactivity. Bryson says that they’re practically indestructible. In 2000, an American scientist named Russell Vreeland even resuscitates 250-million-year-old bacteria trapped in ancient salt deposits.

Most textbooks divide the world into plants and animals, but they barely mention bacteria. In the late 19th century, German naturalist Ernst Haeckel suggests that bacteria need to be included as a third category of organism, but it takes until the 1960s for biologists to embrace the idea. The plant versus animal division also doesn’t suit organisms like fungi, mildews, and yeasts, as they are considered plants but have more in common with animals because they don’t use photosynthesis, but they consume the plant or rock that they grow on. Slime molds also coalesce into slugs that can crawl to another location before reverting back to something more like a plant form.

In 1969, an ecologist named R. H. Whittaker proposes dividing life into not two, but five branches or “kingdoms”: animals, plants, fungi, monera (bacteria) and protista (meaning everything else).  Many biologists, however, dislike the vagueness of the “protista” kingdom, which functions as a sort of vague catch-all for things they can’t classify well, like slime molds. Carl Woese subsequently studies bacteria genes and argues that bacteria are actually several different types of unrelated organisms. In 1976, he redraws the tree of life with not five, but 23 categories, but his efforts are largely ignored for focusing too much on the microbial world, which botanists and zoologists deem irrelevant.

Nonetheless, Bryson thinks that Woese’s system shows us how incredibly diverse life is, and how most of the diversity happens at the “small, unicellular, and unfamiliar” level. This means that complex organisms, like humans, are essentially “side branches” of the real story. Creatures that we can see with the naked eye are only three of 23 categories, and 80 percent of the total biomass of all living things is made up of microbes.

Most illness symptoms don’t come from microbes, but from our immune systems. In an effort to kill the invading microbes, our immune systems also damage some of our own tissues, making us unwell. The body also diverts energy toward making extra white blood cells, which are needed to attack invading bacteria. Some bacteria also inadvertently cause damage when they wander into the wrong part of the body. For instance, one type of bacteria normally causes strep throat—but if it gets past the throat’s lining, it become completely resistant to antibiotics and consumes the body from inside out. Bryson thinks that we’d handle bacteria much better if we didn’t flood the world with antibiotics so often, which causes bacteria to evolve resistance to antibiotics.

In the early 1960s, William Stewart, the United States Surgeon General claims that humans can “close the book” on infectious diseases because penicillin has become fully effective against all strains of staphylococcus bacteria. But unbeknownst to him, around the same time, 90 percent of those strains begin developing an immunity to penicillin. In fact, humans haven’t developed a new antibiotic since the 1970s. Even more alarmingly, in 1983, an Australian doctor named Barry Marshall discovers that deadly stomach ulcers and many stomach cancers are bacterial in origin. It takes over a decade for his suggestion to become scientifically accepted. Bryson thinks that it won’t be long before we lack an effective antibiotic for any bacteria because of our “carelessness” in overusing antibiotics.

Bacteria can also get sick when they’re invaded by viruses called “phages.” Viruses aren’t alive, but they burst into life when they find a host and hijack the genetic materials of living cells to reproduce. Viruses account for many diseases, including smallpox, rabies, and HIV. Viruses can also become active and then mysteriously vanish, or lie dormant before suddenly surfacing. The Spanish Flu pandemic of 1918 (which likely killed up to 100 million people) arose as multiple simultaneous outbreaks around the globe, far more quickly than people could travel back then. It triggered a worldwide pandemic in under a week, meaning it wasn’t spread person-to-person but must have been already present worldwide and somehow activated, though it’s unclear how.

New, deadly viruses crop up all the time and often spread in inexplicable ways. For instance, in 1969, a doctor who was studying Lassa Fever microbes in a Yale University lab came down with the disease and survived, while a lab technician who had no direct exposure also contracted the disease and died. Bryson notes that today’s globalized culture of air travel “invite[s] epidemics”—humans may not be so lucky the next time we have a pandemic on our hands.