Minds without language represent number through space: Origins of the mental number line

Mapping numbers onto an oriented space is a widely known and replicable finding in human adults. Critically, this phenomenon appears to be modulated by culture and, therefore, it has been long believed to be the result of education and human invention. Recent developmental and comparative studies are challenging, however, this assumption by shedding light on the origins of this phenomenon. We will review evidence for the presence of basic number-space mappings in human infants, humans in isolated cultures, as well as in other non-human species such as monkeys and the domestic chick. These populations lack the symbolic tools that have been so far considered determinants for the presence of number-space mappings, thus offering a unique opportunity to explore the origins, evolution and development of numerical representations. Finally, we will describe a testable working hypothesis on the factors that contribute to the emergence of a ‘mental number line’ in a mind without language.