We suggest the greenbeard effect is unlikely drive the evolution of altruism. Examples of the greenbeard effect are likely to be in pleiotropic genes in microbes or in cases where something “special” prevents the breakup of LD. And a greenbeard trait may be present without having caused altruism.

We also find that when altruism is favored via spatial structure (i.e., “classic” kin selection), then signaling and discrimination can also evolve and be in positive linkage disequilibrium (LD), even though the greenbeard effect did not cause the evolution of altruism…

We formally demonstrate the importance of various forms of pleiotropy in favoring the evolution of altruism by the greenbeard effect. In particular, pleiotropy between altruistic behavior and a signaling trait is necessary to substantially favor altruism via the greenbeard effect…

First viewed as a theoretical oddity, recent empirical examples and models could leave one with the impression that the greenbeard effect is an underappreciated phenomenon. But models often make “extra” assumptions about pleiotropy and spatial structure that may lead to interpretation challenges…

The greenbeard effect, first proposed by Hamilton and then elaborated by Dawkins, suggests that a gene that simultaneously 1) leads to altruistic behavior, 2) provides a signal, and 3) discriminates to only cooperate with others sharing the signal can lead to the stable evolution of altruism…

We showed that an unusual equilibrium, originally found in models of signaling in economics, is evolutionarily important. You can have communication that is "partially honest" where people *sometimes* lie and where they are *sometimes* believed. This is called the hybrid equilibrium.