Read the passage below and answer the question.
Linguists studying the historical divergence of the Sino-Tibetan language family have long debated whether shared structural traits among disparate dialects stem from genealogical inheritance or centuries of intense contact. Early typological models posited that tonal systems emerged independently as a compensatory mechanism following the loss of syllable-final consonants. However, recent comparative work utilizing phylogenetic phonology demonstrates that tone in Proto-Sino-Tibetan was already present as a contrastive feature rather than a late secondary development. This finding undermines the traditional assumption that structural simplicity inevitably precedes tonal complexity in Asian linguistic evolution. Nonetheless, some scholars contend that cross-linguistic lexical borrowing has blurred the boundaries between inherited traits and areal diffusion. Ultimately, isolating genetic relationships requires identifying regular sound correspondences that resist horizontal transfer across speech communities.
Select the sentence in the passage that presents empirical evidence challenging a long-held hypothesis regarding the origins of tonal features.
Answer: However, recent comparative work utilizing phylogenetic phonology demonstrates that tone in Proto-Sino-Tibetan was already present as a contrastive feature rather than a late secondary development. / However, recent comparative work utilizing phylogenetic phonology demonstrates that tone in Proto-Sino-Tibetan was already present as a contrastive feature rather than a late secondary development