Tracing the initial diffusion of maize in North America

Abstract

Abstract Domesticated from a wild teosinte grass in southern Mexico more than 6,000 years ago, maize ( Zea mays ssp. mays L.) is today the world's single most important food crop. In this chapter I follow the initial diffusion of this major domesticate from its origin north through Mexico into the southwestern United States and then across the southern Plains into eastern North America, and consider its evolution under human selection during its long journey. Maize provides a well-documented example of a domesticate that was not part of a crop complex carried into new regions by expanding agricultural societies, but rather was exchanged, unaccompanied by other domesticates, from group to group. Keywords : Maize, domestication, North America, crop diffusion INTRODUCTION Domesticated from a wild teosinte grass in southern Mexico more than 6,000 years ago, maize ( Zea mays ssp. mays L.) is today the world's single most important food crop, with a recent annual harvest of more than 818 million metric tons (Varshney et al. 2012: Table 1). In this chapter I look at the early history of this major crop and follow its initial diffusion northward through Mexico into the southwestern United States and then across the Great Plains into the eastern woodlands of North America. A general temporal framework for the spread of maize throughout the Americas now exists, based on direct small-sample accelerator mass spectrometry (AMS) radiocarbon dating of cob and kernel remains recovered from sites scattered across this vast geographical area (Blake 2006). While this general spatial-temporal map of maize diffusion is still very much a work in progress (see ancientmaize.com), it does bring into clearer focus a wide range of questions, many of which are still unanswered, regarding the rates, routes, and mechanisms of initial human diffusion of the domesticate, its evolution under human selection, its adaptation to new environments, and the wide range of different ways in which it was added into and eventually came to dominate the subsistence economies of small-scale societies throughout North America. SOUTHERN MEXICO: THE START OF THE JOURNEY Populations of a wild teosinte grass that grow today along the central Balsas River valley in southern Mexico ( Zea mays ssp. parviglumis Iltis and Doebley) have been identified as being phylogenetically most closely allied with maize, and are considered to be the present-day descendants of its probable wild progenitor (Matsuoka et al. 2002).