Numbers involve various functions, capacities, regions, and connections of the brain. Here we will focus on those important to understanding how numbers emerge and become elaborated, particularly through the use of material forms but also in regard to spoken forms of numbers:

• Numerosity is the innate sense of quantity that humans share with many other species. In humans and nonhuman primates, numerosity is a function of the intraparietal sulcus, a region of the parietal lobe. Numerosity governs what we can and cannot see, quantity-wise, and this influences both our need to use material forms and how we use them.

• Categorizing is the ability that groups or differentiates objects according to the similarities or dissimilarities of their properties, relations, or functions, while abstraction is the process of deriving general concepts and rules from specific properties, relations, or functions. Small sets of objects – singles and pairs – have quantities that are perceptible, and the similarities and dissimilarities of these properties as shared between sets are the plausible basis for concepts of one and two. These concepts are then expressed materially through the fingers, or verbally by describing or naming an object that exemplifies the quantity.

• The mental number line (MNL) is the ability to conceptualize numbers as arranged along a linear continuum. The MNL might be an innate tendency for representational structure that influences numerical conceptualization and expression, or it might be an effect of interacting with material forms like writing, a debate that is currently unsettled in the literature.