In his 1844 "Paris Manuscripts", Karl Marx famously defined humans as "creatures of need" or "needy creatures" who experienced suffering in the process of learning and working to meet their needs. These needs were both physical needs as well as moral, emotional and intellectual needs. According to Marx, human development is characterized by the fact that in the process of meeting their needs, humans develop new needs, implying that at least to some extent they make and remake their own nature. This idea is discussed in more detail by the Hungarian philosopher Ágnes Heller in "A Theory of Need in Marx" (London: Allison and Busby, 1976). Political economy professor Michael Lebowitz has developed the Marxian interpretation of needs further in two editions of his book "Beyond Capital".