Let me get more serious, and answer a question from Noah Smith about what David Graeber means with his book Debt:
The rational kernel inside the bullshit goes roughly like this:
Humans have evolved to be gift-exchangers--beings that maintain our societies by engaging in gift-exchange relationships with kin, close friends, and immediate neighbors. Why? For two big reasons: First, to keep us all pulling roughly in the same direction. Second, to take advantage of the division of labor. There are powerful psychological mechanisms that urge us to engage in such gift-exchange relationships, and to keep such gift-exchange relationships reciprocal--in rough balance.
When agriculture and cities are invented, things get weird: rather than just gift-exchange relationships with thick-tie counterparties--kin, close friends, and immediate neighbors--we find ourselves engaged in weird thin one-sided gift-"exchange" with kings, priests (& gods).