Hieratic developed as a cursive form of hieroglyphic script in the Naqada III period of Ancient Egypt, roughly 3200–3000 BC.[4] Although handwritten printed hieroglyphs continued to be used in some formal situations, such as manuscripts of the Egyptian Book of the Dead, noncursive hieroglyphic script became largely restricted to monumental inscriptions.

So it sounds like Hieroglyphics were used as an everyday eriting system, and over thousands of years this system slowly emerged.

Also a cool fact, the letter A is actually an upside down hieroglyphic called Aleph that shows a cows face with horns.

Wikipedia