The book takes an anthropological/sociological look at the idea of altruism, gift giving, and community to find where the history of animal and mankind these ideas have come from. Ridley notes how a certain species of bat will go out looking for food, return to the nest, and share food that they have with other bats who did not find food. Since the bats are not guaranteed to find food when they go out hunting, this provides the community with an insurance or "shared risk" policy that helps them all stay helathy. However, they keep track of who they have shared food with and if someone becomes a "free rider" on the system then the rest of the bats will stop sharing with them. Sounds an awful lot like the 1996 "Welfare to Work" and change from "entitlement" to "Temporary Assistance" kinds of changes that were made to welfare programs in the US.
Another interesting part of the book was a review of a set of Australian tribes that each produced different goods which they would trade with each other. They didn't need to trade - they could have all produced the items themselves and not had to trade. Ridley theorized that they forced themselves to specialize, to become reliant on each other, because it reduced the chances that the tribes would fight with each other. Ever hear of the Smoot-Hawley tarriffs (and their contemporaries) which probably helped usher in World War II? What about the establishment of the European Common Economic Zone (the commercial side of the EU) as a means to foster inter-reliance and reduce the chances of war. Would Germany, France, and England go to war today? Not as long as trade depends on it. There are certainly other reasons for a country/state to specialize, but as the US has shown with our Strategic Oil Reserves countries generally only specialize to a point and then will try to maintain some of the capability in an area to maintain a smidgen of independence.