Is there such a thing as a 'free lunch'?

... is it an assumption in anthropology that reciprocity is a zero-sum game? ... if so, why do we play it? ... that is, if there's no "free lunch" to be had from playing the reciprocity game, what is its evolutionary worth? ...

Its worth is social stability. All cultural animals do it. Evolutionary worth is not only measured in the individual it is measured in the species, and ours would never have been successful without the culture created for cooperative living. This zero-sum-game does not promote personal gain it promotes group cohesivness.

... but if everybody is a winner (everybody gets a "free lunch"), and there are no losers, then the game of reciprocity is by definition not a zero-sum game ...

:flowers::flowers: Indeed. Not only is it not true that nobody gets a free lunch, but apparently everybody gets a lunch, at least.