3 papers on the evolution of cooperation (Science)

In Science, Volume 314, Issue 5805, December 8 2006

The Puzzle of Human Sociality
Robert Boyd
p. 1555

Five Rules for the Evolution of Cooperation
Martin A. Nowak
p. 1560

Group Competition, Reproductive Leveling, and the Evolution of Human Altruism
Samuel Bowles
p. 1569