No Innate Number Line in the Human Brain

Many authors in the field of numerical cognition have adopted a rather nativist view that all humans share the intuition that numbers map onto space and, more specifically, that an oriented left-to-right mental number line (MNL) is localized bilaterally in the intraparietal sulcus of the human brain. We review results from archaeological and historical (diachronic) studies as well as cross-cultural (synchronic) ones and contends that these claims are not well founded. The data actually suggest that the MNL is not innate. We argue that the MNL-and number-to-space mappings in general-emerges outside of natural selection proper requiring top-down dynamics that are culturally and historically mediated through high-order cognitive mechanisms such as fictive motion, conceptual mappings, and external representational media. These mechanisms, which are not intrinsically numerical and usually are acquired through education, are not genetically determined and are biologically realized through the systematic consolidation of specific brain phenotypes that support number-to-space mappings.