Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [45]
Kropotkin’s intellectual grandchildren asked how competition among individuals could give rise to behavior that benefits entire groups. Fish join together into giant schools that move like a single organism. Sterile ants tend the offspring of their queen. A meerkat will stand guard so that its companions can nose around for food. If a meerkat acquired a mutation that made it stand high to keep watch over its companions, it would become easier prey. Even if natural selection could produce these selfless behaviors, biologists wondered, how could it prevent individuals from exploiting the altruism of others?
For E. coli the evolution of cheating is no mere thought experiment. When a colony runs out of food, the bacteria engage in a complicated cooperative dance as they enter a stationary phase. The microbes send signals to one another to synchronize their actions as they collapse their DNA and halt their production of proteins. By entering the stationary phase together, the bacteria improve the chances that at least some of them will survive until conditions improve, even though many of them may die along the way. Yet Roberto Kolter of Harvard and a former student, Marin Vulíc, discovered that some bacteria do not dance to the same dying tune.
Vulíc and Kolter discovered that mutants arose in their E. coli colony that could rouse themselves from the limbo of the stationary phase and start to feed. They fed not on sugar but on the amino acids excreted by their dormant companions. As some of the stationary bacteria died, they burst open. The mutants then fed on their proteins and DNA. The diet of the mutants was meager, but it was enough to allow them to reproduce. Over the course of several weeks the cheaters’ descendants came to dominate the entire population.
This betrayal was not a rare fluke. Time and again when Vulíc and Kolter starved E. coli, cheaters evolved and thrived. They did so according to the fundamental rules of modern evolutionary biology: through random mutations and the competition among individuals for reproductive success. One has to wonder: If it is so easy for cheaters to triumph, how can cooperation survive at all?
STRENGTH IN NUMBERS
In the 1950s, some scientists explained cooperation in animals with an idea that came to be known as group selection. They argued that a large group of unrelated animals could outcompete another group, just as individuals outcompete other individuals. The adaptations that allow some groups to outreproduce other groups should become more common over time. Group selection could produce traits and behaviors that benefit the many, not the few. In some bird colonies, for example, only a third of the adults might reproduce in a year. Group selectionists argued that the birds are restraining themselves so that the colony will not get too big and destroy its food supply. They even saw death as resulting from group selection, clearing away old individuals so that young ones can get enough food to reproduce.
Group selection was popular for a time. People began to speak of behavior that was for the good of the species. But by the 1960s, critics were beginning to demolish the theory. They pointed out that group selection can produce benefits only slowly—far more slowly than the changes created by natural selection acting on individuals, as with the rise of cheaters. George Williams, an evolutionary biologist at the State University of New York, Stony Brook, distilled many of these arguments into a devastating assault. In his 1966 book, Adaptation and Natural Selection, Williams argued that the group-selection arguments were often the result of lazy thinking. If scientists couldn’t see how natural selection produced an adaptation, it was likely they had simply failed to think seriously enough about the question.
Williams declared that most aspects of biology, no matter how puzzling, were the result of strict natural selection working