You by William B. Irvine

Author:William B. Irvine
Language: eng
Format: epub
Publisher: Oxford University Press
Published: 2018-07-15T00:00:00+00:00

PART III

The Atomic You

13

You Are What You Eat, Ate

So far, we have taken you to be a person, a member of a species, and a collection of cells, but these aren’t the only ways in which you can be understood. Ask a physicist what you are, and the likely response will be “a collection of atoms.” The physicist might go on to reveal that if you weigh, say, 155 pounds (70 kilograms), you are composed of approximately 6.7 × 1027—6.7 billion billion billion—of them.1

At birth, you might have weighed 9 pounds (4 kilograms) and been comprised of 0.4 × 1027 atoms. Where did the additional 6.3 × 1027 atoms come from? The naive answer to this question, offered by a surprising number of people, is that these atoms “are just there” or that your body somehow made them. Such responses indicate a failure to appreciate one of the most basic principles of physics, the Law of Conservation of Mass: although mass can be moved around, it can’t be created or destroyed—not, at any rate, in the normal course of things.2 This means that you didn’t create any of the atoms in you. You simply borrowed them from the outside world. And when you are done with them, that is where they will return.

When an atom enters a living thing, various chemical processes go to work on it. As a result, a solitary atom might become part of a molecule, and an atom that was already part of a molecule might become part of a different molecule. The chemical transformations in question can have spectacular results. Monarch butterflies, for example, are comprised primarily of atoms that formerly belonged to the milkweed leaves that, as caterpillars, they fed on. Likewise, silk is comprised primarily of atoms that formerly belonged to the mulberry leaves that silkworms fed on.

There is an old saying that you are what you eat. Atomically speaking, this is true: the atoms that comprise you almost all come from the foods you eat and beverages you drink.3 But this aphorism also applies to other animals. Consequently, if you are a carnivore, besides being what you eat, you are what you eat, ate. Eat free-range chicken, and some of the atoms you are ingesting probably belonged to one of the bugs that the chicken hunted down. (Eating such bugs is thought by some to play a role in making free-range chickens tastier than their commercially grown counterparts.) Eat a lobster, and some of the atoms you are ingesting might previously have belonged to the decaying fish that the lobster scavenged.

It is natural to think of the atoms that comprise you as being “your” atoms, but in fact they had long histories before becoming part of you; indeed, some of them have been around for nearly 13.8 billion years. And when you die, these atoms won’t cease to exist. They will continue to exist in your remains, or they might move on to become part of some other living thing. In all likelihood they will outlast you by billions of years.

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