The research, he added, showed that San Lorenzo did not appear to be importing artifacts emblematic of other cultures or that regional contemporaries were exchanging such material with one another. The city on the artificial plateau seemed to be the hub of regional culture, and central, he said, to understanding the origin and development of complex society in Mesoamerica.

Richard A. Diehl, of the University of Alabama, wrote in Science that the findings "provide powerful support for the mother-culture school," adding, "San Lorenzo thus dominated in the commercial relationships and attendant spread of Olmec iconography and belief systems."

But Diehl, a proponent of the mother school and the author of "The Olmec," published last year, said in an interview that the "connections we are seeing may not have lasted more than a generation, perhaps the time of a particular ruler and, at most, not more than a century or century and a half." The Blomster research dealt with pottery from the latter half of the early formative period of Mesoamerican culture, which extended from 1500 B.C. to 900 B.C. The last centuries of this period were the time of San Lorenzo's ascendance, but afterward the city was largely abandoned and the Olmec hub gravitated to La Venta, nearby in what is now the state of Tabasco

Blomster collaborated with Dr. Hector Neff, an archaeologist at California State University, Long Beach, and Dr. Michael D. Glascock, of the Research Reactor Center at the University of Missouri. The Missouri center analyzed the pottery and clay samples from San Lorenzo and six other Mexican sites from the era of Olmec prominence.

Proponents of the sister school are not letting the interpretation of the new research go unchallenged. They may be a minority in Mesoamerican studies but are a vocal and formidable one, including such stalwarts as Kent V. Flannery and Joyce Marcus of the University of Michigan and David C. Grove, a professor emeritus at the University of Illinois.

Grove disputed Blomster's conclusions, saying the research demonstrated only that Olmec pottery was traded, not that trade disseminated Olmec political and religious concepts around the region. Others questioned the claim that no pottery of other cultures had been found in San Lorenzo.

The mother-culture advocates, said Susan D. Gillespie, a Mesoamerican archaeologist at the University of Florida who is married to Grove, were "flogging a dead horse, the idea that the Olmec invented civilization, carried it to all of Mesoamerica and it's the basis of the Maya."