Opuntia ficus-indica is one of the few cactus crops. O. ficus indica has been used for human food as early as 9000 to 12000 years ago, probably as a fruit and vegetable just as it is used today. Perhaps it was also used as a medicine or to host cochineal for dye making. The domestication story of O. ficus-indica may tell us something about the Amerindians who domesticated it.
O. ficus-indica is related to a group of wild, tree-like prickly pears that grow in central and southern Mexico, either of which is believed to be the center of domestication. The crop started there even though the plant has spread to most continents in essentially frost-free areas. For instance, it has spread to Sardinia and even Madagascar where its fruit is enjoyed.
One scientist (see Additional Reading, below) studied the DNA of the various species as well as many modern cultivars of O. ficus-indica. There are many types of O. ficus-indica and their DNA shows how they might be related. The studies show that O. ficus-indica is related to O. streptacantha, O. hypiacantha, O. leucotricha, O. megacantha, and perhaps other wild Opuntia species.
Modern O. ficus-indica is thought to have been created by hybridization between these various species. Thus, O. ficus-indica is not a single species, but rather it is a mix of species. The various hybrids were probably selected by humans for their various fruit qualities: sweetness, size, lack of spines, etc. This selection led to the many varieites that we have today. It is possible that wild hybrids were selected, but it is also possible that humans controlled the crosses and deliberately created hybrids.
Additional Reading: Origins of Opuntia ficus-indica