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One of today's most influential theories of language development and acquisition assumes that the human faculty of language is made-up of three components: syntax, phonology, and semantics. Of these components, the syntactic one may be exclusive of humans, while some specific aspects of the semantic and phonological ones may be not. One implication of this division of the language faculty is that aspects of the semantic and phonological systems could also be found in non-human animals, with their function not necessarily being related to communication. Even though not all the scientific community accepts such explanation of the components of the language faculty, diverse academic groups that do so, have been doing research with humans, non-human primates, rodents, birds, and even with cats, for the last 25 years or so. Usually, the purpose of this type of studi es has been to determine what human capacities related to speech have emerged from different precursor systems that were already present in ancestral species, and would have been inherited by men, which components of language are specifically human, which are specifically linguistic, and which ones could be domain-general mechanisms or have served originally for other purposes. Several of these studies imply the existence of a universal division of languages according to rhythmic considerations, known as isochrony. According to this concept, each natural language possesses stable units of constant duration that occur regularly, making it sound in a particular way. But isochrony is not the only universal language feature that can constitute a valid variable in this sort of study. Some characteristics of intonation may also be. Specifically the declarative and interrogative intonation contours, which have been considered a universal phenomenon present in comparable ways in all natural languages. In this regard, though in the different languages of the world the distinction between declaratives and interrogatives can be marked by means of morphsyntactic modifications and intonation, not be marked by intonation, or be only marked by intonation, it is believed that there is a universal tendency to use rising intonation contours to indicate questions (especially in the case of unemphatic yes / no questions) and falling intonation contours to indicate statements. This phenomenon would be related to certain non-linguistic universal codes shared by the human broad phylum, and derived from biologically determined relations. However, while there are numerous investigations in the newborns' and infants' general speech perception processes, in perception of intonation of declarative and interrogative sentences in adults, and in Comparative Psychology of language, studies with infants and newborns in terms of the discrimination of questions and statements are insufficient, and studies on this topic on animal models are, as far as we know, non-existent. In this paper we theoretically validate the comparative study of the perception of intonation contours for questions and statements in infants and in nonhuman animals. We conclude that is feasible and relevant to increase the study of the infants' perception of declarative and interrogative intonation contours, with meaningful variations with respect to the experiments already done, such as the length of the utterances, the type of speech register, the words order, the use of grammatical auxiliaries, the ages of the participants, and the experimental methods. Moreover, it is also desirable to make that same kind of perceptual studies of intonation on animal models, such as rats, birds and monkeys. Pursuing these objectives would make it possible to deepen the knowledge about the language components that are unique for humans and those that are shared with other species. It also could shed some light on the form-function relationships in the phonological component of the language, and about the linguistic universals and precursors. [ABSTRACT FROM AUTHOR]