Mesoamerican food agriculture is defined by the milpa cropping system, consisting of maize (Zea mays L.), common bean (Phaseolus vulgaris L.), and squash (Cucurbita spp.).
In recent years, a domestication center for maize has been proposed in the Balsas River basin in west-central Mexico, raising the question whether the Balsas basin was also the center of origin for Mesoamerican food agriculture in general.
A group of researchers from the Univ. of California, Dep. of Plant Sciences conducted a survey of genetic diversity for 26 microsatellite markers in a representative sample of 155 wild and domesticated common bean from its Mesoamerican gene pool.
They found that most Mesoamerican domesticated accessions clustered in a single group, suggesting a single domestication. Furthermore, the most closely related wild beans to the domesticated clade originated from a restricted region in the Rio Lerma–Rio Grande de Santiago basin in west-central Mexico, distinct from the Balsas basin.
Although wild maize and Phaseolus beans grow together in the wild, the researcher said that they appear to have been domesticated in different regions to be reunited later on in a single cropping system. The group believes that crop domestications in Mesoamerica may have a diffuse rather than a single geographic origin and archaeological and ecological investigations into the origins of agriculture should be refocused from the arid eastern half of Mexico to the west-central part of the country.
Kwak, Myounghai, Kami, James A., Gepts, Paul, The Putative Mesoamerican Domestication Center of Phaseolus vulgaris Is Located in the Lerma-Santiago Basin of Mexico, Crop Sci 2009 49: 554-563.
Published online 17 March 2009 in Crop Sci 49:554-563 (2009), © 2009 Crop Science Society of America, 677 S. Segoe Rd., Madison, WI 53711 USA.
Figure from the article: Geographic distribution of wild bean populations closest genetically to the Mesoamerican domesticated gene pool of common bean in west-central Mexico. Yellow lines represent state boundaries. Purple dots: populations most closely related to the domesticated gene pool. Green dots: other wild bean populations analyzed in the study