We propose an explanation of cooperation among unrelated members of a socia
l group in which cooperation evolves because it constitutes an honest signa
l of the member's quality as a mate, coalition partner or competitor, and t
herefore results in advantageous alliances for those signaling in this mann
er. Our model is framed as a multi-player public goods game that involves n
o repeated or assortative interactions, so that non-cooperation would be a
dominant strategy if there were no signaling benefits. We show that honest
signaling of underlying quality by providing a public good to group members
can be evolutionarily stable, and can proliferate in a population in which
it is initially rare, provided that certain plausible conditions hold, inc
luding a link between group-beneficial signaling and underlying qualities o
f the signaler that would be of benefit to a potential mate or alliance par
tner. Our model applies to a range of cooperative interactions, including u
nconditionally sharing individually consumable resources, participating in
group raiding or defense, and punishing free-riding or other violations of
social norms. (C) 2001 Academic Press.