This paper considers a dynamic model of the evolution of open source software projects, focusing on the evolution of quality, contributing programmers, and users who contribute customer support to other users. Programmers who have used open source software are motivated by reciprocal altruism to...

Transplants of donated stem cells save the lives of many patients with blood diseases. Donation is somewhat painful, but rarely has lasting adverse effects. Patients can accept transplants only from donors with compatible immune systems. Those lacking a sibling match must seek donations from the...

Transplants of donated stem cells save the lives of many patients with blood diseases. Donation is somewhat painful, but rarely has lasting adverse effects. Patients can accept transplants only from donors with compatible immune systems. Those lacking a sibling match must seek donations from the...

This paper surveys the literature on group selection. I describe the early contributions and the group selection controversy. I also describe the main approaches to group selection in the recent literature; fixation, assortative group formation, and reproductive externalities. -- Altruism ; spite...

There are currently debates both about the ability to measure the value of moral sentiments and the nature of benefit-cost analysis. Moral sentiments can be reasonably measured in many situations and their consideration can improve benefit-cost analysis in any case. This argument is presented by...

We conduct field experiments in a large real-world social network to examine why decision-makers treat their friends more generously than strangers. Subjects are asked to divide a surplus between themselves and named partners at varying social distances, but only one of these decisions is...

We examine how economic incentives affect pro-social behavior through the analysis of a unique dataset with information on more than 14,000 American Red Cross blood drives. Our findings are consistent with blood donors responding to incentives in a "standard" way; offering donors economic...

A substantial body of research suggests that economists are less generous than other professionals and that economics students are less generous than other students. We address this question using administrative data on donations to social programs by students at the University of Washington....

From 1917 to 2012, donations by high-income households in the USA have moved inversely with income inequality. This association contradicts historical narratives and prevailing theory, both of which that imply that high-income households donate rising income shares when inequality increases. The...