Representing Something Out of Nothing: The Dawning of Zero.

Zero stands for emptiness, for nothing, and yet it is considered to be one of the greatest achievements of humankind. This review first recapitulates the discovery of the number zero in human history, then follows its progression in human development, traces its evolution in the animal kingdom, and finally elucidates how the brain transforms 'nothing' into an abstract zero category. It is argued that the emergence of zero passes through four corresponding representations in all of these interrelated realms: first, sensory 'nothing'; then categorical 'something'; then quantitative empty sets; and finally the number zero. The concept of zero shows how the brain, originally evolved to represent stimuli ('something'), detaches from empirical properties to achieve ultimate abstract thinking.