Finding plant remains that survive the high temperatures, rainfall, and mold common in the tropics is extremely difficult. Instead, scientists study so-called phytoliths, hardened pieces of silica formed by plants as protection against herbivores and pathogens. The size of the phytoliths is an indicator of their source plant's history: wild Cucurbita plants (which include squash and gourds), for example, have significantly smaller inclusions than their farmed counterparts have. Dolores R. Piperno of the Smithsonian Tropical Research Institute and Karen E. Stothert of the University of Texas at San Antonio collected fossilized Cucurbita phytoliths from archaeological sites in southwestern Ecuador. By comparing the samples to 150 wild and domesticated modern species from 100 different locations, the researchers determined that gourds dating to between 10,000 and 12,000 years ago were cultivated
Cucurbita plants, which are rich in oil and protein, were a favorite among the earliest farmers in various parts of both South America and Mesoamerica. The authors conclude that in addition to possibly pushing back the date of plant domestication, their findings also suggest that there was no single center of agricultural origins in South America.