We model happiness as a measurement tool used to rank alternative actions. Evolution favors a happiness function that measures the individual’s success in relative terms. The optimal function is based on a time-varying reference point—or performance benchmark—that is updated...

A sender randomly draws a “prospect” characterized by its profitability to the sender and its relevance to a receiver. The receiver observes only a signal provided by the sender and accepts the prospect if his Bayesian inference about the prospect’s relevance exceeds his opportunity cost....