views entered the mainstream as a result of the neoclassical synthesis developed by John Hicks. The rise of Keynesianism, and its incorporation into mainstream economics, reduced the appeal of heterodox schools. However, advocates of a more fundamental critique of neoclassical economics formed a school of post-Keynesian economics. Heterodox approaches often embody criticisms of perceived "mainstream" approaches. For instance: feminist economics criticizes the valuation of labor and argues female labor is systemically undervalued; green economics criticizes instances of externalized and intangible ecosystems and argues for them to be brought into the tangible capital asset model as natural capital; and post-keynesian economics disagrees with the notion of the long-term neutrality of demand, arguing that there is no natural tendency for a competitive market economy to reach full employment. Other viewpoints on economic issues from outside mainstream economics include dependency theory and world systems theory in the study of international relations. Historical economic thought Modern macro- and microeconomics are young sciences. But many in the past have thought on topics ranging from value to production relations. These forays into economic thought contribute to the modern understanding, ranging from ancient Greek conceptions of the role of the household and its choices to mercantilism and its emphasis on the hoarding of precious metals. Ancient economic thought Chanakya (Kautilya) Xenophon Aristotle Qin Shi Huang Wang Anshi Islamic economics Islamic economics is the practice of economics in accordance with Islamic law. The origins can be traced back to the Caliphate, where an early market economy and some of the earliest forms of merchant capitalism took root between the 8th–12th centuries, which some refer to as "Islamic capitalism". Islamic economics seeks to enforce Islamic regulations not only on personal issues, but to implement broader economic goals and policies of an Islamic society, based on uplifting the deprived masses. It was founded on free and unhindered circulation of wealth so as to handsomely reach even the lowest echelons of society. One distinguishing feature is the tax on wealth (in the form of both Zakat and Jizya), and bans levying taxes on all kinds of trade and transactions (Income/Sales/Excise/Import/Export duties etc.). Another distinguishing feature is prohibition of interest in the form of excess charged while trading in money. Its pronouncement on use of paper currency also stands out. Though promissory notes are recognized, they must be fully backed by reserves. Fractional-reserve banking is disallowed as a form of breach of