Natural selection has favored the development of a human language so rich in information, that, additionally to meaning, we can also identify the speaker`s sex, emotional state, age, health and social status. Selection has also favored accents and local languages, because they allow the identification of group members (and the exclusion of nonmembers from the group’s resources). The brain uses rules to extract that information, and these rules can fail when applied to alien accents and languages, interpreting, for example, anger or infantilism where there are none.

Keywords: intonation, length of sounds, language, human evolution, natural selection