Beyond the marketplace, nearly all human relationships involve give-and-take, and all such relationships break down when one or both parties do too much taking and not enough giving. In fact, the tension between individual and collective interest arises not only between us but within us. As noted above, complex cells have been cooperating for about a billion years. Nevertheless, it is not uncommon for some of the cells in an animal’s body to start pulling for themselves instead of for the team, a phenomenon known as cancer.
