Why do most linguists reject the Altaic hypothesis as a proven genetic relationship?

The Altaic hypothesis, which proposes that Turkic, Mongolian, and Manchu-Tungus languages share a common genetic origin, remains a subject of significant debate among linguists. While some scholars support the classification based on systematic sound correspondences and structural similarities, many others reject it as a proven genetic relationship.12

The primary reasons for this rejection include:

• Areal Convergence and Borrowing: Many linguists argue that the similarities observed between these languages are not the result of a shared ancestral protolanguage but are instead due to prolonged geographic proximity, areal convergence, and extensive lexical borrowing over centuries of contact.12
• Structural Similarities: Critics point out that common features—such as vowel harmony, subject-object-verb word order, and the use of suffixes—are typological traits that frequently arise through language contact rather than through common inheritance. Such structural parallels are not considered a valid basis for establishing a genetic relationship.3
• Lack of Demonstrable Evidence: For a genetic relationship to be proven, linguists require evidence that matches in phonology, vocabulary, and grammar cannot be attributed to chance or contact. Many scholars believe that reliable, systematic sound correspondences have not been successfully demonstrated for the Altaic group, rendering the hypothesis indemonstrable or highly speculative.41