Agriculture arose during a period of profound global climatic and ecological change following the end of the Pleistocene. Yet, the role of phenotypic plasticity – an organism's ability to change its phenotype in response to the environment – and environmental influences in the dramatic phenotypic transformations that occurred during plant domestication are poorly understood. Another factor possibly influential in agricultural origins, the productivity of crop plant wild progenitors in Late Pleistocene vs. Holocene environments, has received increasing attention recently and merits further investigation. In this study, we examined phenotypic characteristics and productivity (biomass, seed yield) in the wild progenitor of maize, the teosinte Zea maysssp. parviglumis H.H. Iltis & Doebley, when it was first exploited and cultivated by growing it in atmospheric CO2 concentrations and temperatures characteristic of the late-glacial and early Holocene periods. Plants responded with a number of attributes uncharacteristic of teosinte in today's environments, including maize-type traits in vegetative architecture, inflorescence sexuality, and seed maturation. Teosinte productivity was significantly lower in late-glacial compared with early Holocene and modern environments. Our evidence indicates that: a) ancestral biological characteristics of crop plant progenitors aren't always predicted from living examples, b) some important maize phenotypic traits were present at initial human exploitation and selection, and c) Pleistocene plant productivity should be considered a significant factor in the chronology of food production origins.