Great question! I am always eager for the opportunity to talk about Anatolian hieroglyphs.
The key word here is "independent." There are of course hundreds of writing systems that have been used over the millennia. Many of these are addressed in The World's Writing Systems edited by Peter Daniels and The Story of Writing by Andrew Robinson. Most of these writing systems were not independent inventions, however, as they were created by people who knew of writing from elsewhere.
Cuneiform and Hieroglyphs in Bronze Age Anatolia: A Brief History
The people of Anatolia first adopted writing in the Old Assyrian period (ca. 2000-1700 BCE). Merchants from the town of Aššur in Upper Mesopotamia traveled to Anatolia via donkey caravan to exchange textiles for gold and silver. Many Assyrians eventually settled down in Anatolia, married Anatolian women, and produced children. We know quite a lot about this time period thanks to the ~20,000 tablets excavated at Kültepe (ancient Kanesh). The names in the letters indicate that the inhabitants of Kanesh included Assyrians, Hattians, Hittites, and Luwians. The political structure of Anatolia in this time period was fairly fractured, and each city-state had its own ruling king and/or queen. The Old Assyrian texts are written in Akkadian using a simplified system of cuneiform (~100 syllabic signs with very few logograms).
With the collapse of the Old Assyrian period came the disappearance of writing in Anatolia. When writing appeared in Anatolia again in the 16th century BCE during the reign of Ḫattušili I, the Hittites were again using cuneiform, this time a style of cuneiform borrowed from northern Syria, perhaps from Alalakh. Since the Hittites were expanding into Syria at this time, this is not too surprising. The Hittites continued to write in Akkadian for the next century or so, but they began producing Hittite inscriptions to accompany the Akkadian versions, and eventually Hittite replaced Akkadian entirely except for diplomatic correspondence and a few religious and literary texts. Hittite scribes continued using cuneiform for various languages (Hittite, Akkadian, Sumerian, Hurrian, Luwian, Palaic, Hattic) until the disintegration of the Hittite empire in the 12th century BCE.
Although cuneiform was always by far the most popular writing system used in Bronze Age Anatolia, the hieroglyphic writing system developed by the Old Kingdom, most evident in the tabarna seals of the Old Hittite land grants. Some scholars would date the development even earlier to the Old Assyrian period based on a few scattered hieroglyphs on pottery and seal impressions, though it is not clear whether they already held their later phonetic and logographic values. In any case, Anatolian hieroglyphs were in use by the 16th century for seals. Many of these seals were digraphic, with a cuneiform inscription running around the edge of the circular seal and the hieroglyphic equivalent in the center.
Anatolian hieroglyphs use the acrophonic principle, which assigns a phonetic value to a symbol using the first phoneme of that word. This is exactly how our own alphabet began. The letter A, for example, is an upside down ox (Semitic alpu), and the letter B is a house (Sem. betu). From the values of Anatolian hieroglyphic signs, it is clear that the system was invented in a bilingual Hittite and Luwian environment. The donkey sign tarkasna- (also used as the phonetic sign ta) comes from Luwian, for instance, whereas the foot sign ti comes from Hittite (tiya- = "to walk, to step").
By the 13th century BCE, Anatolian hieroglyphs were used not only for seals but also for monumental rock inscriptions. This development was almost certainly derived from the long Egyptian tradition of monumental inscriptions, as the Hittites were in close contact with the Egyptians in this time period.
With the disintegration of the Hittite empire came the cessation of writing in cuneiform. As the empire fragmented into smaller Neo-Hittite/Syro-Hittite kingdoms, kings continued to carve monumental inscriptions using Anatolian hieroglyphs. The hieroglyphic inscriptions from Carchemish are particularly numerous and significant. In addition to hieroglyphic inscriptions, Aramaic and Phoenician inscriptions have been found at Syro-Hittite sites. Anatolian hieroglyphs were used until around 700 BCE, by which time southern Anatolia and northern Syria were firmly under Assyrian control. Cuneiform was used once more in the region, this time for Neo-Assyrian monumental inscriptions.
Independent Inventions of Writing
So why is the Anatolian hieroglyphic writing system not considered an independent invention of writing? Simply put, it is because the scribes of Anatolia already knew of writing, first from Assyria in the Old Assyrian period (ca. 2000-1700 BCE) and then from northern Syria in the Old Kingdom (ca. 1600-1400 BCE). Although Anatolian hieroglyphs are unique to Anatolia, they were created by people who already knew the principles of writing and had an established literary tradition.
The writing systems of the Aegean - Cretan hieroglyphs, Linear A, and Linear B - were also invented by people who were in touch with literate cultures, especially Egypt. For example, an inscribed alabaster lid of the Hyksos king Khyan was found at Knossos.
Similarly, the inventions of writing systems in Iran, such as the short-lived Linear Elamite and the very controversial Konar Sandal tablets of the Jiroft culture, are believed to have been inspired by Mesopotamian cuneiform.
A writing system is considered an independent invention of writing if it evolved without knowledge of other writing systems. Historians have traditionally pointed to five independent inventions of writing:
Mesopotamian cuneiform
Egyptian hieroglyphs
The Indus script
Chinese characters
Mesoamerican writing systems
Mesopotamian cuneiform, Egyptian hieroglyphs, and the Indus script developed by around 3200 BCE, although lengthy texts appeared several centuries later. The Oracle bones of the Shang dynasty are the earliest attestations of Chinese writing and date to around 1250 BCE, slightly later than Linear B in the Aegean. Finally, the origins of the Mesoamerican writing systems are still poorly understood, but the Cascajal Block may push the invention of writing back to at least the first millennium BCE.
That said, it should be emphasized that only in the cases of China and Mesoamerica can we say with certainty that writing evolved independently. Whether Mesopotamian cuneiform inspired the development of Egyptian hieroglyphs and the Indus script is a long-running and still unresolved issue.
