constant source of ATP, so the reaction “assembly” line has to operate 24/7.

There are, of course, different possible arrangements of the assembly line—that is, different combinations of reactions that could produce ATP (as with many networks, there being multiple pathways to get to a hub). An important question in cellular biology is whether cells should prefer to produce ATP as rapidly as possible, or as efficiently as possible (that is, with pathways that produce greater quantities of ATP from the same amount of raw material, getting more ATP bang for the buck). Some reaction pathways are faster but more wasteful than others, posing a trade-off for cells desiring to achieve an optimum metabolism.

The best strategy, a game-theoretic analysis shows, depends on the various other organisms in the vicinity competing for resources. Where competition is present, game theory recommends fast but wasteful ATP production, a prediction that contradicts straightforward notions of optimizing resource allocation. After all, if a population of microbial cells are competing for food, it would seem best for the group for each microbe to make the most efficient use of the available food supply, so there will be enough to go around. But game theory says otherwise—it’s another example of the Prisoner’s Dilemma in action. What’s best for the individuals doesn’t compute to be the overall best deal for the group.

“This paradoxically implies that the tendency of the users to maximize their fitness actually results in a decrease in their fitness—a result that cannot be obtained from traditional optimization,” Pfeiffer and Schuster point out. “In the framework of evolutionary game theory, slow and efficient ATP production can be seen as altruistic cooperative behavior, whereas fast and inefficient ATP production can be seen as selfish behavior.”11

But it’s also a mistake to assume that cells will always act selfishly to enhance their survival odds. Game theory math suggests that in scenarios where a microbe’s neighbors eat a different kind of food (so there is no competition for a single resource), more efficient production of ATP at the expense of speed would be a better survival strategy. Actual observations confirm that cells typi-

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