• Choose a category
• All
• Classic-Fiction

By Root 1322 0

have colored throats, which may be orange, yellow, or blue. The orange-throated lizards are big fighters; they establish large territories with several females. The blue-throated lizards are medium sized; they defend small territories, holding just a few females, which they can guard carefully. The yellow-throated males are small and sneak around for mates, taking advantage of the fact that they look like females. Each type of male can outcompete one type but not the other. The yellow-throated males can sneak past the orange-throated males because the territories of the orange-throated males are so big. The yellow-throated males cannot use the same strategy against the blue-throated males because the blue-throated males stay close to their females and are bigger than the yellow-throated males. But the blue-throated males lose against the orange-throated males because the orange-throated males are bigger.

Over a period of six years, each type of male goes through a population cycle. When the orange-throated males become common, natural selection favors yellow-throated males, which can sneak off with their females. But once yellow-throated males become common, the biggest benefits go to blue-throated males, which can fight off the yellow-throated males and father lots of baby lizards with their few females. And in time, natural selection favors the orange-throated males again.

When scientists at Stanford and Yale discovered the E. coli version of the rock-scissors-paper game in 2003, they suggested that it may turn out to be particularly common. Chemical warfare is a frequent strategy in nature, particularly among organisms that are too small or too immobile to use other sorts of weapons. Trees poison their insect visitors, corals ward off grazers, and humans and other animals produce antibodies to fight off pathogens. The race to develop better poisons and defenses, as well as the added dimension of the rock-scissors-paper game, can foster the evolution of diversity. Scientists have long known that a single strain of E. coli may dominate the gut for a few months, only to later shrink away, making way for a rarer strain. The colicin war may be one force behind this cycle.

E. coli may be able to spontaneously evolve a harmonious food web. But when it comes to weaving Darwin’s tangled bank, war may be just as good as peace.

DEATH COMES TO ALL

Not long ago, E. coli was immortal. That’s not to say it was invulnerable. The bacteria can die in all sorts of ways—devoured by protozoans, starved for years in a famine, or ripped open like a water balloon by the prick of a colicin needle. But decades of gazing at E. coli left scientists convinced that death is not inevitable. Left to its own devices, E. coli remained eternally young. Here was one way, at least, in which E. coli was fundamentally different from us. Our bodies slide into decay on a relatively tight schedule. Our immune system lets more viruses and bacteria invade our bodies unchallenged. Our brains shrink; our bones grow brittle; our skin droops.

The question of why we slide this way toward death preoccupied George Williams. He was so fascinated by it that he charted his own decline. Beginning at age fifty-two, he would go once a year to a track near his home on Long Island and time how long it took him to run 1,700 meters. Some years he ran a little faster than he had the previous year, but over the course of twelve years he gradually slowed down. Why, Williams wanted to know, was he declining so steadily? If he had to die, why couldn’t he stay young and fit until his body suddenly gave out? And if he did have to get old, why did his decline follow the particular downward curve that it did? Why hadn’t he run so slowly in his twenties instead of in his fifties?

After all, Williams could look to the natural world for an endless supply of alternatives. A clam may live for four centuries. At the other extreme are salmon, which return in peak condition to the streams where they were born. They find a mate, have baby salmon, then promptly grow old at catastrophic