Language is what distinguishes adult human beings from both human infants and other primates. The development of language in the species and in the child are two of nature's most profound mysteries. The aim of this collaborative project is to shed light on these mysteries by assessing similarities between natural language and spontaneous non-linguistic knowledge in both human infants and other primates (macaques and cotton-top tamarins). The project also aims to determine how the non-linguistic knowledge differs from language, for this will tell us what special features of language must be accounted for in analyses of the evolution and acquisition of natural languages. The focus of the research is one restricted arena of conceptual and linguistic knowledge: natural number. Three aspects of nonlinguistic representation of number will be studied: (1) the nature of infant and non-human primate representations of integers; (2) the representations of quantifiers such as `an,` `another,` and `more`; and (3) the criteria for individuating objects and assessing numerical identity (sameness in number). The proposed studies have several specific goals. First, given that human infants, macaques, and tamarins pass simple tests of `addition` and `subtraction,` a series of experiments will be carried out to uncover the nature of the underlying representations. Second, the upper numerical limit of the addition/subtraction ability will be determined, for all three subject populations. Third, experiments will be conducted to probe whether all three populations are tracking number of objects in the addition/subtraction studies or total mass/volume. Fourth, studies will be carried out to assess whether nonhuman primates and human infants spontaneously represent which of two numerical quantities is larger, and whether this ability is subject to the same upper limit as the addition/subtraction ability. Finally, the relationship between the acquisition of language and the conceptual representations associated with basic object kinds (e.g., cup, apple) will be explored in all three species. The findings will shed light on fundamental problems of development and evolution. Specifically, the project will provide an explicit account of how humans spontaneously develop numerical competence from birth to the first year of life, and will also generate an evolutionary explanation for why numerical competence evolved, and when during primate phylogeny it originated.
