Shadows of Forgotten Ancestors

* Humans are newly evolved. Our availability on a global scale as hosts for parasites is very recent. In the absence of medical countermeasures, we might expect, sometime in the future, the evolution of new kinds of microorganisms that pull our strings more artfully than any rabies virus could ever do.* It’s not hard to see how the components of this “fight-or-flight” response are all adaptive—evolved to get you through the crisis. That feeling of cold and emptiness at the pit of your stomach, for example, results from a reallocation of blood from digestion to the muscles.* True, of course, only for sexual organisms. Asexual beings, reproducing by splitting in two, cannot enhance the fitness of their descendants through a spirit of self-sacrifice.* Humans do this routinely. Large multi-ethnic states are revealingly called “fatherland” or “motherland.” Leaders encourage patriotic fervor—the word “patriotic” comes from the Greek for father. Especially in monarchies, it was easy to pretend that the nation was a family. The distant and powerful king was like many fathers. Everyone understood the metaphor.

Chapter 7

WHEN FIRE WAS NEW

Not I, but the world says it:

All is one.

HERACLITUS¹

The oxygen in the air is generated by green plants. They vent it into the atmosphere and we animals greedily breathe it in. So do many microbes and the plants themselves. We, in turn, exhale carbon dioxide into the atmosphere, which the green plants eagerly inhale. In a profound but largely unremarked intimacy, the plants and animals live off each other’s bodily wastes. The atmosphere of the Earth connects these processes, and establishes the great symbiosis between plants and animals. There are many other cycles that bind organism to organism and that are mediated by the air—cycles in nitrogen, for example, or sulfur. The atmosphere brings beings all over the world into contact; it establishes another kind of biological unity to the planet.

The Earth started out with an atmosphere essentially free of the oxygen molecule. As bacteria and other one-celled organisms arose, 3.5 billion years ago or earlier, some harvested sunlight, breaking water molecules apart in the first stage of photosynthesis. The oxygen, a waste gas, was simply released into the air—like emptying a sewer into the ocean. Resolutely independent, liberated from reliance on nonbiological sources of organic matter, the photosynthetic organisms proliferated. By the time there got to be enormous numbers of them, the air was full of oxygen.

Now oxygen is a peculiar molecule. We breathe it, depend on it, die without it, and so naturally have a good opinion of it. In respiratory distress, we want more oxygen, purer oxygen. As modern words (“inspire,” literally, breathe in; “aspire,” breathe toward; “conspire,” breathe with; “perspire,” breathe through; “transpire,” breathe across; “respire,” breathe again; and “expire,” breathe out) and Latin proverbs (such as Dum Spiro, spero, while I breathe, I hope) remind us, we associate many aspects of our nature with breathing. The word “spirit” —in all its incarnations (“spiritual,” “spirited,” alcoholic “spirits,” “spirits” of ammonia, and so forth)—also derives from the same Latin word for breath. Our fixation with breathing comes ultimately from considerations of energy efficiency: The oxygen we respire makes us about ten times more efficient in extracting energy from food than, say, yeast are; they know only how to ferment—breaking sugar down to some intermediate product such as ethyl alcohol rather than all the way back to carbon dioxide and water.*

But as a blazing log or a burning coal reminds us, oxygen is dangerous. Given a little encouragement, it can vandalize the intricate, painstakingly evolved structure of organic matter, leaving little more than some ash and a puff of vapor. In an oxygen atmosphere, even if you don’t apply heat, oxidation, as it’s called, slowly corrodes and disintegrates organic matter. Even much sturdier materials such as copper or iron tarnish and rust away in oxygen. Oxygen is a poison for organic molecules and doubtless was poisonous to the beings of the ancient Earth. Its introduction into the atmosphere triggered a major crisis in the history of life, the oxygen holocaust. The idea of organisms that gasp and choke to death after being exposed to a whiff of oxygen seems counterintuitive and bizarre, like the Wicked Witch of the West in The Wizard of Oz melting away to nothing when a little water falls on her. It’s the ultimate version of the adage “One man’s meat is another man’s poison.”†