At their most basic, the answers provided by modern genomic science to questions about populations depend on data. Data offer such a crucial lens through which to observe and begin to understand our similarities to, and differences from, one another that one of my major arguments in Our Genes is simply this: Data matter. Field data, yielded by measuring features of natural populations, help make evolutionary theory mathematically and statistically explicit by viewing evolution as the change of allele frequencies across generations. Evolutionary geneticists use many kinds of data to develop and select among mathematical models, and to subject explanatory and predictive evolutionary genetic theory to empirical tests.1To test and improve such models, evolutionary geneticists depend on measurements and data provided by field samples and laboratory experiments, fed through statistical machinery.