A Short History of Nearly Everything: Chapter 24 Summary & Analysis

Bryson says that cells are a “thing of wonder”— even the simplest are “far beyond the limits of human ingenuity.” When a cell divides, each new cell contains complete copies of the instructions needed to do everything in the body. It takes 47 cell divisions to create the 10,000 trillion cells needed to make a human. Even a simple yeast cell contains the same number of components as it takes to build a Boeing 777 airplane, and yeast cells are “nothing compared with human cells.” Human cells do everything from making hair grow, metabolizing food, and allowing people to form thoughts their minds.

We understand “little of how cells do the things they do.” Some scientists even argue that we only have a competent grasp of two percent of human cells. There are several hundred types of human cell, ranging from nerve cells containing several feet of curled-up filaments to rod-shaped photocells that enable vision. The average human cell is 20 microns wide (0.02 millimeters) and most last for about a month before being replaced—except liver cells, which last for years, and brain cells, which last for the entire lifespan (though their components are frequently renewed). In fact, a person’s cellular components are completely replaced every nine years (meaning that on the cellular level, a person is never more than nine years old).

Robert Hooke first describes (and names) the “cell” in 1665. Microscopes of the time can only magnify the world about 30 times. Curiously, an uneducated Dutch linen draper named Antoni van Leeuwenhoek invents one that can magnify things 275 times, but he keeps his instruments secret and only shares drawings of his observations. Leeuwenhoek’s drawings prompt a craze among scientists. Fellow Dutchman and respected scientist Nicolaus Hartsoecker is even convinced he can see “tiny preformed men” in sperm cells, and he claims that humans are giant blow-up versions of miniature cellular selves. It takes scientists until 1839 to realize that all living matter is cellular, and until the 1860s for famed scientist Louis Pasteur to conclude that life cannot arise without cells, laying the foundations for modern biology.

To Bryson, a cell is a “nightmarish place” somewhere between a city and a factory with ceaseless activity, electrical energy, and no gravity (this force doesn’t have a feasible impact at the microscopic scale). Cells combine the food and oxygen we consume to generate electricity. If one imagines that atoms were pea-sized, a cell would be half a mile wide, and its outer membrane (which is made of fat) would seem as rigid as iron. The cell would contain millions of objects ranging between the size of a baseball and the size of a car, moving as fast as bullets.

At this scale, it would be impossible to stand in a cell without being torn to shreds. Each strand of DNA is damaged every 8.4 seconds from all the action, and it has to perpetually repair itself to keep the cell alive. Enzymes perform up to 1,000 tasks a second, and they work like sped-up worker ants that build, inspect, and rebuild molecules. At actual speed, a cell is an incomprehensible place—but slowed down, it’s more like a place where millions of objects perform millions of mundane tasks while perpetually bumping into one another.

The human heart has to pump 75 gallons of blood an hour to keep all the cells in a human body oxygenated. Mitochondria (tiny bacteria living in our cells) consume the oxygen and convert it into a molecule called ATP, which is like a little battery pack that gets passed around the cell and that powers everything up. Each cell contains about a billion ATP molecules, which are drained of power and replaced every two minutes.

When a cell is no longer needed, it’s programmed to eat itself by breaking down its molecules so that they can be reused. Sometimes, a cell won’t comply, and it starts dividing and multiplying instead, which is what we call cancer. Bryson says that cancerous cells are essentially “just confused cells.” This happens so rarely—considering the decades of a lifespan—that cells really are “wondrous” in functioning so consistently en masse. Cells don’t think—their activities are automatic—but they’re nonetheless harmonious and ordered across the entire human body. Cell activity is directed by a molecule called DNA, which Bryson will discuss next.