Phaseolus (Fabaceae) in archaeology: AMS radiocarbon dates and their significance for pre-Colombian agriculture

Beans of several species were domesticated in tropical America thousands of years ago, to be combined with maize and other crops in highly successful New World agricultural systems. Radiocarbon dates on charcoal associated wi th Phaseolus in archaeological sites, in Mexico and Peru indicated the pres ence of domesticated beans as early as 10 000 years ago. However, direct da tes on the beans and pods themselves by accelerator mass spectrometry (AMS) do not provide evidence for the cultivation in Mexico of common beans, P. vulgaris, and teparies, P acutifolius, before about 2500 B.P, in the Tehuac an Valley, and of common beans about 1300 years ago in Tamaulipas and 2100 years ago in the Valley of Oaxaca. AMS dates support the presence in the Pe ruvian Andes of domesticated common beans by about 4400 B.P. and lima beans by about 3500 B. P. and lima beans by about 5600 B.P. in the coastal valle ys of Fern. The late appearance of common and lima beans in the Central Hig hlands of Mesoamerica supports the importance of missing evidence that may be obtained from prehistoric agricultural sites in western Mexico and in Ce ntral America which are located within the range of the wild populations of these species. Additionally, biochemical studies of subsamples of the date d specimens should be carried our in order to extend the molecular evidence for the independent domestication of North and South American common beans .