Arrival of the Fittest: Solving Evolution's Greatest Puzzle by Andreas Wagner Page A

language while infants and can still recognize some of its words.) 9
    Detoxifying your waste is good, but recycling it is even better, and nature excels at that too. The nitrogen waste of animals—ammonia or urea—fertilizes plants. The very oxygen we breathe is a waste product of photosynthesis. 10 And every gram of feces is teeming with billions of bacteria feeding on the molecules in it: One man’s waste is a bacterium’s treasure. Each one of these bacteria harbors a metabolic text, ancient or recent, to break down molecules, extract energy and chemical elements, and build new life from them.
    Innovative metabolic texts are just as ubiquitous in extreme environments—extremely hot, extremely cold, excessively dry, highly caustic, exceedingly radioactive, super-salty, and so on—as in temperate ones. Bacteria in particular can thrive in boiling water and in ice, in highly corrosive sulfuric acid and in crushing oceanic depths. To survive, they had to innovate, and many of their innovations—you guessed it—are metabolic.
    Without these innovations, extreme environments would kill bacteria just as easily as they kill us. Too much salt, for example, kills cells, because it forces water out through osmosis and prevents enzymes from doing their job—they need water as a lubricant. To clog this drain, metabolism produces molecules with exotic names such as ectoine and glycine betaine that cannot leave a cell as easily as water does, and that can stand in for water molecules lost through osmosis. They keep proteins lubricated. To make these molecules, cells need only a few extra enzyme-catalyzed chemical reactions that start with common molecules like the amino acid aspartate. Add these reactions to a metabolism, and you have a leg up in the most hostile environment. Halophilic bacteria—the name comes from the Greek for “salt-loving”—can survive salt concentrations of 30 percent, ten times higher than the seawater that kills us when we drink it. They can even live around and inside salt crystals. 11
    Extreme environments are no picnic, but life can be even harder if you face predators and parasites, and especially if escaping them is not an option. Any ordinary plant would be an immovable feast for many organisms, from insects and worms tunneling through the soil to slugs and other herbivores aboveground. Because plants can’t so much as twitch in their own defense, they develop chemical weapons, molecules so toxic that animals avoid them. Plants are not alone in using chemical warfare, but they are especially adept at it, perhaps because they are, literally, rooted to one spot.
    These defensive molecules are metabolic innovations, because they require new combinations of chemical reactions to synthesize them. One of them is the nicotine produced by tobacco plants that some of us blissfully inhale through cigarettes, even though it is so toxic that some farmers use it as an insecticide. But plants had the idea first, as a group of German scientists recently showed. When they artificially lowered the amount of nicotine that tobacco plants produce, insects developed a voracious appetite for the plants. They attacked the plants more often, ate more leaves, and grew faster. The plants, in turn, lost three times more leaves than normal plants to their attackers. 12
    Nicotine is only the best known of more than three thousand similar alkaloids—a catchall term for organic molecules built around nitrogen atoms, including caffeine and morphine—that plants use in chemical defense. And although they are numerous, alkaloids are only one among several kinds of chemical warfare molecules. Others include the astringent tannins that make your mouth feel dry and shriveled when you eat unripe fruit. 13 Tannins bind very tightly to plant proteins and prevent our gut from digesting these proteins, which discourages us from feeding on them in the first place. Cyanogenic glycosides are especially nasty chemical defense molecules