I bought Nonzero by Robert Wright last night, and am enjoying it a lot. By applying the game theory concept of 'non-zero-sumness' to human and biological interaction, he shows how communication and trust are necessary to establish non-zero-sum exchanges, such as markets, information sharing (conversations) and reciprocal exchanges of hospitality. Here he is discussing the Shoshone Indians, traditionally regarded as 'the Irreducible minimum of human society':

A successful Shoshone rabbit hunt would culminate in a "fandango". Sounds like a spontaneous and carefree celebration - and indeed fandangos featured, as one anthropologist put it, "gambling, dancing...philandering". Still, as scholars have noted, the fandango was eminently utilitarian. First, it distributed fresh meat among the rabbit hunt's various kinds of workers. Second, it was an occasion for trading such valuables as volcanic glass. Third, it was a chance to build up a network of friends. (Even the ritual exchange of knickknacks, though economically trivial, can be a way to bond, forming conduits for future favor-swapping of greater moment). Fourth, the fandango was an opportunity to trade information about, say, the location of food.
All of these are non-zero functions, and the last is especially so. Giving people data, unlike giving them food or tools, has no inherent cost. If you know of a place where the supply of pine nuts far exceeds your own familiy's needs, it costs nothing to share the information with a friend. So too if you know the location of a den of poisonous snakes. Sometimes, of course, surrendering information is costly (as when the supply of nuts doesn't exceed your family's needs). Still, data are often of little or no cost and great benefit; swapping them is one of the oldest froms of non-zero-sum interaction. People by their nature come together to constitute a social information processing system and thus reap positive sums. The fandango, the academic conference, and the Internet are superficially different expressions of the same deep force.

More extracts at http://www.nonzero.org, but buy this and read it, you won't regret it.