Something very strange is going on on this planet. A single chemical system-the system of DNA-rules this planet utterly and is taking over more of it every day. Evolutionary theory implies that advancement is based on random happenings, random couplings of molecules, and the random atom-flicks of mutation. Evolutionary theory also implies that a competition between a menagerie of variations determines who and what will survive. But, as I mentioned, there's only one molecular system on this planet that, so far as we can see, has ever achieved even the faintest sliver of life. It's the twisted spiral chain of DNA. With no other clans to game against, the family of DNA has been forced to create its own competition, its own form of family play. That's why we see the dna on this planet stretching its tendrils into every nook and cranny despite a lack of competing biochemical systems. But there's another reasons that dna has extruded oddities as different as bacteria, begonias, beatles, and you and me. DNA does not need challengers from outside the nucleotide tribe. Why? It's up against something bigger-mother nature. To stay alive and thrive, DNA has had to duck, hop, and barrel-roll, dodging the slings and arrows of an outrageous universe. Among other things, nucleic acid replicators have been compelled to race against a larger cosmic force...that which produces periodic mass extinctions on this peculiar globe of ours. Think of just one life-form extinguisher--the cycles caused by the Malankovitch Effect--shifts in climate that take place roughly every 22,000, 41,000, and 100,000 years. Malankovitch Effects are caused by the peculiarities of the earth's tilt, its orbit around the sun, and in the case of the 100,000 year cycles by the periodic passage of our solar system through a particularly dusty patch of galactic schmootz. Under normal circumstances, our plucky little planet manages to absorb roughly 30 million kilograms of space dust without much trouble. But every 100,000 years we pass through a cloud of interplanetary powder that doubles or even triples this tonnage. The result is the sort of weather run amock that can wipe out such sluggish children of DNA as, say, that vast range of outrageously alien-looking creatures known as Ediacaran fauna. The DNA ensemble may lack for competing life-systems, and thus not be poked into motion by the alleged Darwinian sine qua non called competition, but it still must run very hard just to stay in place and run even harder to get ahead. Or, to put it differently, from dust we come and to dust we shall return, but in the meantime dust may be a natural selector that occasionally tosses whole suites of species away.

To survive, the DNA system has been forced to outmaneuver mass extinctions of gargantuan size. It's done so by generating phenotypes able to turn the hurdles of even the most impossible conditions into trellises. Bacteria have learned to live off sulfur and rock six miles beneath the ocean and two miles beneath the surface of the earth. Humans have figured out ways to live in frigid climates no other primate has been able to endure. A good thing-since Malankovich disasters are based on inexorable forces like the earth's tilt in its trips around the sun, the wobbles of its orbit, and the periodic passage of the solar system through clouds of cosmic dust. Those children of DNA that haven't worked out a niche in which to hide or triumph, die. Human cultures are also going to need to develop highly flexible strategies so they can overcome the longterm obstacles of climate change. We've been skimping on such things as the development of alternative energy sources and the upgrade of old infrastructure since the oil shock of the early 1970s. The Bush Administration is one that insists on returning to our old oil-based approaches. This may produce more trouble than we know. Environmental groups have tried to stop our move toward the genetic engineering of crops that can grow in soil with a high salt content and very little moisture. The oil lobby managed to eliminate government funding for solar and renewable energy research during the Reagan Administration. Yet we'll need these things and more to make it through massive weather changes that may dry up the lands we farm today or may soon demand that we use different forms of energy in very different ways.

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