Unequal exchange is used primarily in Marxist economics, but also in ecological economics (more specifically also as ecologically unequal exchange), to denote forms of exploitation hidden in or underwriting trade. Originating, in the wake of the debate on the Singer–Prebisch thesis, as an explanation of the falling terms of trade for underdeveloped countries, the concept was coined in 1962 by the Greco-French economist Arghiri Emmanuel to denote an exchange taking place where the rate of profit has been internationally equalised, but wage-levels (or those of any other factor of production) have not. It has since acquired a variety of meanings, often linked to other or older traditions which perhaps then raise claims to priority. In the works of Paul A. Baran, and subsequently adopted in the dependency approach of Andre Gunder Frank, there is a related but distinct concern with the transfer of values due to superprofits. This did not refer to the terms of trade, but to the transfer taking place within multinational corporations (called "monopolies"). Versions of unequal exchange originating within the dependency tradition are commonly based on some such concern with monopoly and center-periphery trade in general. Here, if unequal exchange occurs in trading, the effect is, that producers, investors and consumers incur either higher costs or lower incomes (or both) in the buying and selling of commodities than they would have, if the commodities had traded at their “real” or "true" value. In that case, they are disadvantaged in trading, and their market position is worsened, rather than strengthened. On the other side, the beneficiaries of the trade obtain a superprofit. This term implies that the beneficiaries of unequal exchange are capitalists or entrepreneurs, whereas as understood by Emmanuel the beneficiaries are the high-wage country consumers or workers. The most renowned of those adopting the term is Samir Amin, who tried to link it to his own argument on the interdependent uneven development of rich and poor countries. Ernest Mandel also adopted the term, although his theory was based rather on that of the East-German Marxist Gunther Kohlmey. The most common approach within Marxism is to talk about unequal exchange whenever unequal labour values are being exchanged (e.g., John Roemer), and this type of approach has then been elaborated in recent decades by ecological economists, based instead on, e.g. ecological footprints or energy. Depending on definition, the historical occurrence of unequal exchange can be traced to