The history of writing traces the development of expressing language by systems of markings and how these markings were used for various purposes in different societies, thereby transforming social organization. Writing systems are the foundation of literacy and literacy learning, with all the social and psychological consequences associated with literacy activities. In the history of how writing systems have evolved in human civilizations, more complete writing systems were preceded by proto-writing, systems of ideographic or early mnemonic symbols (symbols or letters that make remembering them easier). True writing, in which the content of a linguistic utterance is encoded so that another reader can reconstruct, with a fair degree of accuracy, the exact utterance written down, is a later development. It is distinguished from proto-writing, which typically avoids encoding grammatical words and affixes, making it more difficult or even impossible to reconstruct the exact meaning intended by the writer unless a great deal of context is already known in advance. The earliest uses of writing in ancient Sumeria were to document agricultural produce and create contracts, but soon writing became used for purposes of finances, religion, government, and law. These uses supported the spread of these social activities, their associated knowledge, and the extension of centralized power. Writing then became the basis of knowledge institutions such as libraries, schools, universities and scientific and disciplinary research. These uses were accompanied by the proliferation of genres, which typically initially contained markers or reminders of the social situations and uses, but the social meaning and implications of genres often became more implicit as the social functions of these genres became more recognizable in themselves, as in the examples of money, currency, financial instruments, and now digital currency. Writing systems Symbolic communication systems are distinguished from writing systems. With writing systems, one must usually understand something of the associated spoken language to comprehend the text. In contrast, symbolic systems, such as information signs, painting, maps, and mathematics, often do not require prior knowledge of a spoken language. Every human community possesses language, a feature regarded by many as an innate and defining condition of humanity (see Origin of language). However the development of writing systems, and their partial replacement of traditional oral systems of communication, have been sporadic, uneven, and slow. Once established, writing systems on the whole change more slowly than their spoken counterparts and often preserve features and expressions that no longer exist