Writing system
Writing systems were preceded by proto-writing, systems of ideographic and/or early mnemonic symbols. The best known examples are:The invention of the first writing systems is roughly contemporary with the beginning of the Bronze Age in the late Neolithic of the late 4th millennium BC. The Sumerian archaic cuneiform script and the Egyptian hieroglyphs are generally considered the earliest writing systems, both emerging out of their ancestral proto-literate symbol systems from 3400 to 3200 BC with earliest coherent texts from about 2600 BC. It is generally agreed that Sumerian writing was an independent invention; however, it is debated whether Egyptian writing was developed completely independently of Sumerian, or was a case of cultural diffusion.
History of writing
The Middle Bronze Age Indus script, which dates back to the early Harappan phase of around 3000 BCE in the Indian subcontinent corresponding to northwestern India and what is now Pakistan, has not yet been deciphered. It is unclear whether it should be considered an example of proto-writing or whether it is actual writing of the logographic-syllabic type of the other Bronze Age writing systems. Mortimer Wheeler recognises the style of writing as boustrophedon, where "this stability suggests a precarious maturity."