IT STARTS WITH a single cell. The first cell splits to bee two and the two bee fourand so on. After just forty-seven doublings, you have ten thousand trillion(10,000,000,000,000,000) cells in your body and are ready t forth as a human being.
1And every one of those cells knows exactly what to do to preserve and nurture you from themoment of ception to your last breath.
You have s from your cells. They know far more about you than you do. Eaecarries a copy of the plete geic code—the instruanual for your body—so itknows not only how to do its job but every other job in the body. Never in your life will youhave to remind a cell to keep an eye on its adenosiriphosphate levels or to find a place forthe extra squirt of folic acid that』s just uedly turned up. It will do that for you, andmillions more things besides.
Every cell in nature is a thing of wonder. Even the simplest are far beyond the limits ofhuman iy. To build the most basic yeast cell, for example, you would have tominiaturize about the same number of pos as are found in a Boeing 777 jetliner andfit them into a sphere just five mis across; then somehow you would have to persuade thatsphere to reproduce.
But yeast cells are as nothing pared with human cells, which are not just more variedand plicated, but vastly more fasating because of their plex iions.
Your cells are a try of ten thousand trillion citizens, each devoted in some intensivelyspecific way to your overall well-being. There isn』t a thing they don』t do for you. They letyou feel pleasure and form thoughts. They enable you to stand and stretd caper. Whenyou eat, they extract the nutrients, distribute the energy, and carry off the wastes—all thosethings you learned about in junih school biology—but they also remember to make youhungry in the first plad reward you with a feeling of well-being afterward so that youwon』t fet to eat again. They keep your hair growing, your ears waxed, your brain quietlypurring. They manage every er of your being. They will jump to your defehe instantyou are threatehey will uatingly die for you—billions of them do so daily. Andnot on all your years have you thanked even one of them. So let us take a moment now tard them with the wonder and appreciation they deserve.
We uand a little of how cells do the things they do—how they lay down fat ormanufacture insulin age in many of the other aecessary to maintain a plicatedentity like yourself—but only a little. You have at least 200,000 different types of protein1Actually, quite a lot of cells are lost in the process of development, so the number you emerge with is reallyjust a guess. Depending on which source you sult the number vary by several orders of magnitude. Thefigure of ten thousand trillion (or quadrillion) is from Margulis and Sagan, 1986.
lab away inside you, and so far we uand what no more than about 2 pert ofthem do. (Others put the figure at more like 50 pert; it depends, apparently, on what youmean by 「uand.」)Surprises at the cellular level turn up all the time. In nature, nitric oxide is a formidabletoxin and a on po of air pollution. So stists were naturally a little surprisedwhen, in the mid-1980s, they found it being produced in a curiously devoted manner inhuman cells. Its purpose was at first a mystery, but then stists began to find it all over theplace—trolling the flow of blood and the energy levels of cells, attag cers andother pathogens, regulating the sense of smell, even assis