Cooperation and fairness in encounters with strangers are puzzling behaviors, since they contradict the law of natural selection. Compelling evidence shows that direct and indirect reciprocity and altruistic punishment are important mechanisms for the evolution of cooperation in the long-term. For short-interaction, cooperation and fairness are explained by theories which assume that individual...

Among the billions of planetary systems that fill the Universe , we would like to know how ours fits in. Exoplanet data can already be used to address the question: How common are Jupiters? Here we discuss a simple analysis of recent exoplanet data indicating that Jupiter is a typical massive planet rather than an outlier. A more difficult question to address is: How common are Earths? However,...