Evolution and the Capacity for Commitment ed. Randolph Nesse:

Commitment is at the core of social life. We live in a social fabric woven from a warp of promises and a weft of threats, and we spend much of our lives deciding which commitments are credible, and trying to manage our own commitments and reputations. Classical economics and sociobiology sometimes seem to suggest that this should not be too hard, because people should generally act in ways that benefit themselves or their genes. While reciprocity and kin selection are indeed powerful principles, attempts to force all behavior into their Procrustean bed have aroused much intellectual consternation and moral indignation. This conflict has deepened the rift between biological and social sciences. Commitment offers a bridge across this chasm. In this book, some of the world’s most distinguished researchers examine the nature of commitment, and the question of whether our capacities for making, assessing and keeping commitments have been shaped by natural selection. Many commitments are fairly straightforward attempts influence others by giving up options and thereby making it worthwhile to fulfill the commitment. Examples include burning your bridges behind you or signing a contract. However many commitments are not enforced by such tangible incentives. These subjective commitments are enforced by pledges of reputation and by emotions. Some are benevolent, such as a promise of life-long love. Others are not, such as a threat to murder a straying spouse. Although some such commitments may seem irrational in the extreme, they nonetheless influence us. Commitment thus offers a possible evolutionary explanation for irrational passions that are otherwise difficult to explain, and for our moral capacities.