American agriculture in worldwide perspective

New data, especially plant microfossils (phytoliths, starch grains, pollen), demonstrate that agriculture is as old in the American tropics as in the early Old World primary centres.^[1202] Plant domestication began in the early Holocene, and the longer-term environmental changes that accompanied the Pleistocene-Holocene transition can be considered the ultimate causal fac­tors behind the development of food production.

In the American tropics, early food producers were semi-sedentary to sedentary, occupying alluvial or wetland-edge habitats. Groups appear to have been organized at the level of family or hamlet, with no evidence for social complexity. Expansion of forests in the neotropics during the early Holocene changed plant distributions, closing formerly open woodlands and altering edge habitats favoured by many starch-rich root and tuber species. Among the human responses indicated by the record of early agriculture are creating and maintaining open habitats for favoured plants, altering mobility patterns as resources expanded or contracted, changing diet in response to changing availabilities of foods, and increasing densities of desirable plants and animals by cultivation/management. The record indicates that in the early Holocene there were frequent and dispersed plant domestications: some were advantageous and early domesticates spread, sometimes widely, through social interactions among foragers and horticulturalists. Cultivation was small­scale, in well-watered settings.

Increasingly productive crops fuelled population growth, which led to the spread of societies dependent on agriculture into new habitats, and creation of built environments for farming. This last is the most visible threshold of the process, having left its mark throughout the Americas on the landscape, in sediment cores, and in numbers of sites. Agriculture eventually spread into all suitable environments in the Americas, with landscape modification and crop improvements opening up or increasing the potential of previously unsuitable or geographically limited environments. With clear evidence that the roots of plant domestication lay in the early Holocene, the challenge now facing us is to expand the palaeoenvironmental and archaeological records of this process, and to better understand people-plant interrelation­ships during the late Glacial period.