What evidence suggests that the speakers of Hittite, Palaic, and Luwian shared a long common history?

The evidence suggesting that the speakers of Hittite, Palaic, and Luwian shared a long common history is primarily linguistic, supported by the observation that these Anatolian languages share a significant number of both linguistic losses and innovations that presuppose a shared past before their divergence.1

Key indicators of this common history include:

• Shared Innovations and Losses: The languages exhibit specific grammatical developments and losses that suggest the ancestral group remained together for a significant period after separating from the parent Indo-European group.1
• Common Vocabulary and Pronouns: They share specific linguistic features, such as a common demonstrative stem (abā-) and the relative-interrogative pronoun kwi- ("who").2
• Shared Cultural Concepts: Comparisons of agricultural terminology indicate that these groups seceded from the parent Indo-European population after developing a common notion of the afterlife, but before establishing a common agricultural nomenclature.1

This evidence supports the theory that the ancestors of these speakers entered Anatolia together, following a common route, before eventually diverging into the distinct languages documented in the 2nd millennium BCE.1