Abstract: The ability to use numbers is one of the most complex cognitive abilities that humans possess and is often held up as a defining feature of the human mind. Alongside the uniquely human symbolic system for representing number we possess an approximate number system (ANS) that is evolutionarily ancient and developmentally conservative. In my talk I will illustrate the signatures of the ANS with experimental data from human babies and nonhuman primates. I will describe behavioral and neurobiological data that demonstrates how the human and nonhuman primate mind privileges numerical information over other types of quantitative information. I will argue that this numerical privilege implicates the biological importance of number in our evolutionary history. Finally, I will offer some empirical evidence for the hypothesis that the primitive number sense serves as a foundation for uniquely human mathematical thought both during development and throughout the lifespan.