Much has been written about our innate language sense and how it has shaped our evolution and our nature, but until now little has been known about what Brian Butterworth calls our "numerosity, " an innate number sense as fundamental to our human nature as language. Indeed, the author argues, to explore human nature at all it is necessary to explore the numerosity of the human brain.Is there a math gene? Butterworth's research strongly suggests there is. Do men and women count differently? What is a mathematical prodigy? Why do some people count on their fingers? Are our methods of teaching math effective or not -- and why? No book has authoritatively answered these intriguing questions before now. Butterworth's unique expertise in both mathematics and psychology has enabled him to write a trailblazing work on our understanding of the mathematical brain that shows why counting is fundamental to our lives and how we comprehend the world. With an engaging and accessible style, What Counts will become as important to mathematics as Stephen Pinker's and Noam Chomsky's writings are to language.