Writing this week (Aug. 1, 2005) in the Proceedings of the National Academy of Sciences (PNAS), a team of scientists led by University of Wisconsin-Madison archeologist James B. Stoltman presents new evidence that shows the Olmec, widely regarded as the creators of the first civilization in Mesoamerica, imported pottery from other nearby cultures. The finding undermines the view that the Olmec capitol of San Lorenzo near the Gulf of Mexico was the sole source of the iconographic pottery produced by the earliest Mesoamerican civilizations.
"At issue here is trade pottery," says Stoltman, an emeritus professor of anthropology and an archeologist more familiar with the ancient native cultures of the Southeastern and Midwestern United States.
The pottery -- and its origins -- is the pivot of a rollicking debate among Mesoamerican archeologists: Were the Olmec, a culture that emerged three millennia ago near what is now Veracruz on the Gulf of Mexico, the "mother culture" to the Maya, Aztec and other civilizations that thrived in succession in pre-Columbian Central America and Mexico?
Or, were the Olmec a "sister culture," one of several in the region whose interrelationships shaped art, religion, political structures and other cultural attributes of ancient Mesoamerica?
For archeologists, pottery is a linchpin for making such judgments. Where pottery was manufactured, who made it, its iconography, and how it traveled over native trade routes from group to group is a critical diagnostic of cultural influence. The distinctive iconography carved into Olmec pottery is presumed to have carried important cultural influences, influences that may have helped shape contemporary and subsequent civilizations such as the Maya.
To answer questions about the origins of Olmec ceramics, scientists have used a variety of techniques. In February 2005, chemical analyses of Olmec pottery were published that strongly suggested the pottery, with its attendant iconography and culture, had a single source: San Lorenzo, the earliest Olmec capitol built on a massive artificial mound near the Gulf of Mexico.
A chemical technique, known as neutron activation, was used to compare the elemental composition of Olmec pottery with pottery from several sites across central Mexico. The results of the tests were published in Science and their correlation seemed to strongly favor the mother culture school of thought -- that Olmec ceramics all came from one place.
Now, however, an old technique brought to bear by Stoltman on an array of pottery fragments from five formative Mexican archeological sites shows that the "exchanges of vessels between highland and lowland chiefly centers were reciprocal, or two way."
The new results were obtained through the use of petrography, a long-established geological technique capable of accurately identifying minerals in a sample. "With this technique, you can identify minerals and rocks, not the elements as you get with neutron activation," says Stoltman, an authority on petrography. "It is a technique that is very accurate for identifying minerals."
The results of the new study show that minerals added to temper pottery came from multiple sites, including the highlands of Oaxaca.
"Pots are a human product," Stoltman explains, adding that temper -- crushed rock, often -- was added to confer plasticity and help pots survive shrinking and drying without cracking.
The geology of the San Lorenzo site is underlain by sedimentary rock, limestone and sandstone, Stoltman explains. Oaxaca and other areas rest on metamorphic rocks. The signature of the geology where the pots were produced, he says, is effectively added with the sand used for tempering.
"These analyses contradict recent claims that the Gulf Coast was the sole source of pottery carved with iconographic motifs," Stoltman says.
The previous chemical analyses, Stoltman argues, could be misleading as potsherds lie in the earth and can lose and gain soluble chemical elements over time. "It's the wrong technique. It's inappropriate for pottery in most cases. These (fragments) have been in the ground for three thousand years."
Among the samples tested by Stoltman, who was blind to the locations from which the pottery fragments were recovered, were pieces that had been found at San Lorenzo and visually -- but not conclusively -- identified as Oaxacan in origin.
"Five of these samples are unambiguously from Oaxaca, demonstrating " Stoltman says, "that some of pottery from San Lorenzo was made elsewhere."
The new findings, Stoltman believes, add some clarity to the interrelationships of cultures in ancient Mesoamerica. But the "mother culture/sister culture" debate is unlikely to ebb.
"It's difficult to give primacy to one culture," he says. "In many ways, their (the Olmec) culture was unique," but it may have only been one part of the cultural equation of the day.
In addition to Stoltman, the corresponding author of the study, co-authors of the PNAS paper include Joyce Marcus and Kent V. Flannery of the University of Michigan, James H. Burton of UW-Madison, and Robert G. Moyle of the American Museum of Natural History.