Market  

"Immanuel Wallerstein characterised the world system as a set of mechanisms, which redistributes surplus value from the periphery to the core. In his terminology, the core is the developed, industrialized part of the world, and the periphery is the "underdeveloped", typically raw materials-exporting, poor part of the world; the market being the means by which the core exploits the periphery." --Sholem Stein

"Physical attractiveness, both as subjectively experienced and objectively measured, operates in accordance with exchange-market rules. Individuals with equal market value for physical attractiveness are more likely to associate in an intimate relationship such as engagement than individuals with disparate values".Who Will Marry Whom?: Theory and Research in Marital Choice (1976) is a book by Bernard I. Murstein.