“The early pictographs evolved in two ways: first, they were the beginning of pictorial art—the objects and events of the world were recorded with increasing fidelity and exactitude as the centuries passed; second, they formed the basis for writing. The images, where the original pictorial form was retained or not, ultimately became symbols for spoken-language sounds.
The Paleolithic artist developed a tendency toward simplification and stylization. Figures became increasingly abbreviated and were expressed with a minimum number of lines. By the late Paleolithic period, some petroglyphs and pictographs had been reduced to the point of almost resembling letters. . . .
The leap from village culture to high civilization occured after the Sumerian people arrived in Mesopotamia near the end of the fourth millennium B.C. . . .
One theory holds that the origin of visible language evolved from the need to identify the contents of sacks and pottery containers used to store food. Small clay tags were made that identified the contents with a pictograph and the amount through an elementary decimal numbering system, based on the ten human fingers.
The earliest written records are tablets from the city of Uruk. They apparently list commodities by pictographic drawings of objects accompanied by numerals and personal names inscribed in orderly columns. An abudance of clay in Sumer made it the logical material for record keeping, and a reed stylus sharpened to a point was used to draw the fine, curved lines of the early pictographs.”

—Phil Meggs & Alston Purvis, Meggs’ History of Graphic Design, 2006.