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

that are produced in cassava or manioc, the important African and South American food plant. 14 Unless you remove these glycosides by cooking or soaking, they release hydrogen cyanide, the active ingredient of the Zyklon B pesticide piped into the “showers” at Nazi extermination camps like Auschwitz-Birkenau. If you ever thought of nature as that idyllic place, the next best thing to the Garden of Eden, a tutorial on chemical warfare in plants will quickly dispel that myth.
    Biochemical warfare molecules like these are metabolic innovations, add-ons to an existing metabolism manufactured by new sequences of chemical reactions that start from common biomass molecules and transform them into potent poisons. Each one requires specific passages of text in a metabolic genotype.

     
    Some of nature’s ways to find new metabolic texts are familiar, because they dominate in large multicellular animals like us. They include the changes accompanying sexual reproduction, which shuffles chromosomes like decks of cards, so that each of our children starts with a new deal. Then there are the spontaneous mutations in a DNA’s letter sequence, arising through chance events such as when photons of ultraviolet radiation smash into the genome, or through highly reactive oxygen radicals that are by-products of chemical reactions and burst the chemical bonds of nearby DNA.
    Neither way to explore the metabolic library is very effective. Since the shuffling of sexual reproduction occurs between highly similar genomes—two human genomes share 99.9 percent of their DNA letter sequence—it is not the most effective way to create new metabolisms. 15 It is like trying to write a new play by changing thirty words in
Hamlet
. And while mutations can create new proteins, including new enzyme catalysts, they are rare, which means the process is rather slow.
    And there is one more reason why metabolic innovation is not swift in large, multicellular animals. A new way of using energy or building organic structures can make its value known only at the speed that it spreads throughout a population, and animals that produce a new generation every few decades—or even every few months—can’t innovate any more rapidly than that.
    All this doesn’t mean that animals like us are completely impoverished when it comes to metabolic innovations. Our bodies, for example, can disarm drugs—like the widely used aspirin, known to chemists as acetylsalicylic acid—through a metabolic process called glucuronidation that renders them less toxic and excretable in urine. Cats and some other carnivores like hyenas lack this enzyme. 16 (Consult a vet before medicating your pet hyena with aspirin.) You may ask why our bodies have this enzyme, which evolution created long before the company Bayer first marketed aspirin in the 1890s. The clue lies in aspirin’s name itself, which comes from an old name for a plant called meadowsweet,
Spiraea ulmaria
. This and many other plants have been used since antiquity for pain relief. What is more, plants containing salicylic acid were part of our ancestors’ diets, such that our omnivoric bodies—unlike those of carnivores like hyenas—needed a way to detoxify it.
    Within the multicellular world, humans are far from the pinnacle of metabolic creation, however, because many animals beat us in other aspects of metabolism. Humans cannot produce vitamin C, and must therefore drink it with a morning glass of orange juice, whereas dogs can make their own. And although we can extract calories from the seeds of grasses like wheat and maize, cows are better at digesting the cellulose in their stalks. To be fair, however—credit where it is due—that miracle of metabolism isn’t really a bovine innovation, but a microbial one: It is the bacteria in the four-stomached cows that convert gigantic cellulose molecules into easily digested glucose.
    Which is a hint that the real geniuses of innovation are the smallest organisms on the