Number systems as upgrades to cultural software for thinking

Numeracy advanced through cultural inventions that upgraded our mental tools: small-scale societies counting '1,2,3, many,' then using stones, body parts, or phalanges as metaphors, then the number line which made zero and negative numbers comprehensible (centuries after counting numbers), and then orthogonal number lines yielding the complex plane—each a reusable cognitive technology teachable to children.