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By Root 1288 0

because they were diverting energy from their growth. But soon the balance tipped. As the bacteria multiplied, they used up the oxygen around them and could not grow as quickly. The glue makers could escape suffocation because they created a rising mound on which their offspring could grow. They could reach higher concentrations of oxygen, which allowed them to grow faster, which in turn allowed them to build their mounds of glue even higher. As a mound grew, it suffocated the older bacteria underneath while their descendants—and thus their genes—lived on. Meanwhile, the bacteria that did not make glue, trapped in the biofilm with no way to escape, were buried by their competitors. In some ways a biofilm may be less like a city and more like a forest, in which trees become wooden towers in order to reach the sunlight and avoid the shade of their rivals.

Conflict and cooperation strike an uneasy balance whenever many cells come together, whether they are E. coli or the cells of our own bodies. We descend from single-celled ancestors that probably looked a lot like amoebas. At some point our ancestors began to form colonies, which gradually evolved into vast collectives, otherwise known as animals. They communicated with one another as they had before, but now their signals caused them to differentiate into different types of cells, forming tissues and organs. Each time a new animal took shape, most of the cells of its body had to make the ultimate evolutionary sacrifice. They would become part of the body, and in that body they would die. Only sperm and eggs had the slightest chance of their genes surviving.

This is not a simple way to exist. In order to form a full-grown body, most cells must divide many times and then stop. Some kinds of cells must not lose the ability to regenerate themselves, but they must multiply only as much as necessary to heal a wound or build a new intestinal lining. Unfortunately, a dividing cell can mutate, just like a dividing E. coli. In some cases, the mutations will turn the cell into a rebel. It will reproduce rapidly, ignoring the signals that tell it to stop. It will produce a mass of insurgent cells, and within that mass new mutations will arise, producing even more rebellious cells. They will develop new tricks for evading the body’s defenses and for manipulating the body so that it brings them new blood vessels in order to supply them with extra oxygen and nutrients. They become cheaters, just like the cheaters that exploit E. coli’s cooperation. We call their success cancer.

PLACE YOUR BETS

When a starving colony of E. coli gets a supply of lactose, there is only one good decision to make: start manufacturing beta-galactosidase and use it to break the lactose down. Some microbes will make the right choice while others will not. The losers keep their lactose-digesting genes shut off, and they continue to starve.

These microbes are all genetically identical, which means that the same genetic circuitry gives rise to both decisions. If natural selection favors genes that boost the reproduction of E. coli, how could it have produced this sort of confusion? That is a difficult question, one scientists have only begun to take seriously. The answer they have now settled on is this: E. coli is a smart gambler.

Every gambler who comes to a racetrack hopes to place a winning bet. The best way to win is to see into the future and know which horse will come in first. But in the real world, gamblers can only hope to winnow down their choices to a few strong horses. Even with this limited selection, they run the risk of losing money. Some gamblers shield themselves against losses by hedging their bets. They wager on several horses in the same race. If one of their horses wins, they get money. They don’t leave the racetrack with as much money as they would have had they bet only on the winner. But the other bets can act as a good insurance policy. If one of the other horses wins, the gambler can still go home with more money than he came with.

Gamblers aren’t the only people who think about