Money and Slavery
"Initially, he notes, most human societies recognize that their constituent individuals cannot be truly bought or sold, and, as such, things such as dowries and bride wealth were paid in a special kind of currency (which he refers to as "social currency") which was generally not negotiable for commodities such as food, simple crafts, etc. Instead, such social currency had the function of rearranging the social relationships of people in the community, but, no matter the form of that rearrangement, each party had responsibilities towards the other.
This begins to shift in societies with the introduction of chattel slavery. In a traditional hierarchical society, even being at the bottom of the totem pole still meant that you existed in a web of mutual obligations with others in the community. However, an individual who has been entirely torn from their social context and purchased by an individual in a community in which they have no connections is an entirely different story. That slave can be treated in almost any manner without social repercussions, and can thus be used (and thought of) in an entirely instrumental way. This, according to Graeber, leads to a whole cascade of consequences that fundamentally changes the way people view the world in general: if humans are negotiable and alienable, so is everything else. The brutal effects of this transformation are illustrated with vivid historical examples from societies as disparate as West Africa and Thailand, and provides the foundation for a fascinating perspective that sees the social, religious, philosophical, and economic characteristics of a variety of historical periods as being heavily influenced by each era's conceptions about the nature of money and debt." (http://cuhistory.blogspot.com/2011/09/book-review-debt-first-5000-years-by.html)
From a review of David Graeber's book, see First_Five_Thousand_Years_of_Debt