PRINCETON, New Jersey — Jesus said that we should give alms in private rather than when others are watching. That fits with the common-sense idea that if people only do good in public, they may be motivated by a desire to gain a reputation for generosity. Perhaps when no one is looking, they are not generous at all.

That thought may lead us to disdain the kind of philanthropic graffiti that leads to donors' names being prominently displayed on concert halls, art museums and college buildings. Often, names are stuck not only over the entire building, but also on as many constituent parts of it as fundraisers and architects can manage.

According to evolutionary psychologists, such displays of blatant benevolence are the human equivalent of the male peacock's tail. Just as the peacock signals his strength and fitness by displaying his enormous tail — a sheer waste of resources from a practical point of view — so costly public acts of benevolence signal to potential mates that one possesses enough resources to give so much away.