Knowledge of number: its evolution and ontogeny.

Mathematical concepts and systems of notation are intertwined with human cultural history. The discovery (or invention) of 0, understanding of negative, rational, and real numbers, and development of the calculus took place over thousands of years. But what of those most fundamental of mathematical objects, the positive integers: 1, 2, 3, 4, 5, ...? Until recently, the consensus was that the capacity to represent the positive integers was also the product of culture, dependent on the uniquely human capacity for language. A new study on the represention of number in animals, on page 746 of this issue (1), along with studies of the representation of number by prelinguistic infants (2), are undermining that consensus.