Why do Semitic and Amazigh languages lack tone systems?

The question of why Semitic and Amazigh (Berber) languages lack tone systems—while many other Afro-Asiatic languages possess them—is a subject of ongoing linguistic debate rather than a settled fact.1

There are two primary scholarly perspectives regarding this divergence:

• Loss of Tonality: Some linguists propose that Proto-Afro-Asiatic was originally a tone language. Under this hypothesis, daughter branches such as Semitic and Amazigh subsequently lost all tonal distinctions over time.1
• Independent Development: Other researchers assume that the ancestral language was a pitch-accent system rather than a full tone language. In this view, tonality emerged independently within the Chadic, Cushitic, and Omotic branches. This development may have been driven by the pitch-lowering effects of certain syllable-initial consonants (tonal depressors) or through long-term contact with speakers of Niger-Congo and Nilo-Saharan languages, which are characterized by genuine tone systems.1

Consequently, the absence of tone in Semitic and Amazigh is either viewed as the result of a historical simplification or as evidence that these branches never developed the tonal features found in other parts of the Afro-Asiatic family.1