The complexity of maize domestication: Maize originated in what is now central Mexico about 9000 years ago and spread throughout the Americas before European contact. Kistler et al. applied genomic analysis to ancient and extant South American maize lineages to investigate the genetic changes that accompanied domestication (see the Perspective by Zeder). The origin of modern maize cultivars likely involved a “semidomesticated” lineage that moved out of Mexico. Later improvements then occurred among multiple South American populations, including those in southwestern Amazonia. Science , this issue p. 1309 ; see also p. 1246

The discovery of large geometrical earthworks in interfluvial settings of southern Amazonia has challenged the idea that Pre-Columbian populations were concentrated along the major floodplains. However, a spatial gap in the archaeological record of the Amazon has limited the assessment of the territorial extent of earth-builders. Here, we report the discovery of Pre-Columbian ditched enclosures in the Tapajós headwaters. The results show that an 1800 km stretch of southern Amazonia was occupied by earth-building cultures living in fortified villages ~Cal AD 1250–1500. We model earthwork distribution in this broad region using recorded sites, with environmental and terrain variables as predictors, estimating that earthworks will be found over ~400,000 km²of southern Amazonia. We conclude that the interfluves and minor tributaries of southern Amazonia sustained high population densities, calling for a re-evaluation of the role of this region for Pre-Columbian cultural developments and environmental impact.

In the highlands of southern Brazil an anthropogenitcally driven expansion of forest occurred at the expense of grasslands between 1410 and 900 cal BP, coincident with a period of demographic and cultural change in the region. Previous studies have debated the relative contributions of increasing wetter and warmer climate conditions and human landscape modifications to forest expansion, but generally lacked high resoltiuon proxies to measure these effects, or have relied on single proxies to reconstruct both climate and vegetation. Here, we develop and test a model of natural ecosystem distribution against vegetation histories, paleoclimate proxies, and the archaeological record to distinguish human from temperature and precipitation impacts on the distribution and expansion of Araucaria forests during the late Holocene. Carbon isotopes from soil profiles confirm that in spite of climatic fluctuations, vegetation was stable and forests were spatially limited to south-facing slopes in the absence of human inputs. In contrast, forest management strategies for the past 1400 years expanded this economically important forest beyond its natural geographic boundaries in areas of dense pre-Columbian occupation, suggesting that landscape modifications were linked to demographic changes, the effects of which are still visible today.

Newly created academic programs at Brazilian universities have provided the impetus for new archaeological projects in southeastern South America during the last two decades. The new data are changing our views on emergent social complexity, natural and human-induced transformation of the landscape, and transcontinental expansions and cultural interactions across the Río de la Plata basin during the Middle and Late Holocene. We concentrate on six major archaeological traditions/regions: the Sambaquis, the Pantanal, the Constructores de Cerritos, the Tupiguarani, the Southern Proto-Jê, and the middle and lower Paraná River. Diverse and autonomous complex developments exhibit distinct built landscapes in a region previously thought of as marginal compared with cultural developments in the Andes or Mesoamerica. The trajectories toward increased sociopolitical complexity flourished in very different and changing environmental conditions. While some groups were pushed to wetland areas during a drier mid-Holocene, others took advantage of the more humid Late Holocene climate to intensively manage Araucaria forests. The start of the second millennium AD was a critical period marked by an increased number of archaeological sites, the construction of ceremonial architecture, and the intensification of landscape transformation; it also was marked by the rapid expansion of influences from outside the La Plata basin. The Amazonian Tupiguarani and Arawak newcomers brought with them significant changes in technologies and social and political structures, as well as novel landscape management practices.