Every human language is 'tonal', i.e., uses tone for some significant purpose. Some languages also happen to use tone at the phonemic layer of perception. This

Every human language is 'tonal', i.e., uses tone for some significant purpose. Some languages also happen to use tone at the phonemic layer of perception. This is a minor difference. Does it surprise you that vowel length in English is phonemically significant? Probably not. Why should a phonemically significant tone be any more surprising?