In the highlands of Mexico in the state of Puebla just 75 miles southeast of Mexico City there exists an archaeological site that is possibly the most controversial in all of Mexico. It is called Hueyatlaco, the location of some amazing discoveries in 1962. Amid the bones of mastodons, extinct camels, mammoths and smaller animals was evidence of human activity and man-made artifacts of flaked flint, quartz and bone. Spearheads were embedded into bones and some of the bones showed evidence of deliberate butchering leading investigators to believe that Hueyatlaco was a “kill site” where animals were hunted and butchered. A team led by Mexican paleohistorian Juan Armenta Camacho, who had grown up in the area, and a young Harvard anthropologist named Cynthia Irwin-Williams investigated the site over several field seasons. They discovered human artifacts in several layers of sediment with the more simple tools in the lower levels and more complex tools in the upper levels.
While excavating the site the investigators realized that they might have a problem dating their findings. Carbon 14 dating up until that time was the most common radiometric dating method in the Americas for assigning ages to archaeological sites. At Hueyatlaco there were no remains of anything containing carbon – wood, charcoal, shell, etc. – to extract dating samples from. The animal bones that were found at the site were all fossilized. Whatever carbon that was contained in them was now gone.
By the mid 1960s it had been theorized that the Hueyatlaco site could be 22,000 years old. If this date were true it would cause all sorts of history and science books to be re-written. The peopling of the Americas, according to the longstanding theory, began some 13,000 to 16,000 years ago when hunters and gatherers from Asia crossed the Bering Land Bridge to North America and migrated southward. Early big game hunters called the Clovis People existed some 13,500 years ago in the Americas and left behind distinctive knapped stone tools. If the Hueyatlaco site were older by some 10,000 years, this site would have revolutionized what scientists and researchers thought about the arrival of humans to the Americas from Asia. Armenta had a big problem on his hands. How to date the site?
In 1966 a young PhD student from Harvard who was looking for an interesting doctoral dissertation joined the team. Her name was Virginia Steen-McIntyre and she was trained in the field of tephrochronology. Tephrochronology is a dating technique that uses discrete layers of volcanic ash from specific eruptions of a given volcano to create a chronological framework in which ancient artifacts or environmental samples can be placed. A layer of ash, for example, can be dated, and thus things occurring within, above and below the layer can be dated with some degree of accuracy. In the area around Hueyatlaco there were several volcanic and pumice layers and the region had hundreds of other volcanic deposits. Some of the volcanic layers had already been dated by using the Carbon 14 dating method which was applied to wood burned during the corresponding volcanic eruptions. Using a microscope and techniques learned at Harvard, Steen-McIntyre’s plan was to match the undated layers at the Hueyatlaco site to the already-dated layers of the nearby volcanoes. It seemed simple enough, but after hundreds of samples and testing spanning years, Steen-McIntyre could find no correlation between the volcanic layers and could not date the site this way. The dates would have to be arrived at through some other method. Steen-McIntyre gave up having Hueyatlaco as the subject of her doctoral dissertation, but the site so fascinated her that she never gave up on Hueyatlaco.
During the ‘60s the site had garnered a lot of attention from the Mexican government and the Instituto Nacional de Antropología e Historia in Mexico City. In 1967 Jose Lorenzo of the instituto claimed that the artifacts at Hueyatlaco were faked and planted at the site. The authorities in Mexico City sent their own scientist to the area and set up test pits near Armenta’s digs to begin their own excavation. Eventually, Armenta’s artifacts were confiscated and moved to Mexico City and he was banned by the authorities from doing any sort of fieldwork of any kind, ever. Armenta’s field partner and co-excavator at the site, Cynthia Irwin-Williams came to Armenta’s defense, but to no avail. In spite of this big bump in the road, the quest to date the site continued.
Irwin-Williams was dead set on believing the date of 22,000 years based on the carbon dating of snail shells associated with a similar kill site very close to Hueyatlaco called Caulapan. A new dating technique called the “uranium series method” had also been applied to two samples from this nearby site and yielded similar dates going back 22,000 years. Irwin-Williams was satisfied that these dates could also apply to the larger, main site of Hueyatlaco, even those these dates did not come as a result of testing items found at Hueyatlaco proper. After those dates were firmly established from Caulapan, a butchered camel pelvis that actually came from Hueyatlaco was tested using the uranium series and the results were astounding.
They came back with a date suggesting the site was almost 250,000 years old. Virginia Steen-McIntyre was excited about the findings, while the now-sole head of the excavation, Cynthia Irwin-Williams was not. She stuck to her original date of 22,000 years old for Hueyatlaco and would not compromise. Steen-McIntyre knew that more tests were needed, so she spearheaded an effort to get more dating done at the site. She also shifted her focus to compare the layers at Hueyatlaco to even older layers of volcanic ash at the nearby volcano.
The next dating method they would use came from the paleoanthropologists in Africa who were using it to date some of the earliest human ancestors yet discovered. This dating method was called “zircon fission-track dating” where small crystals of zircons in the layers at Hueyatlaco were tested. The date that came back from the tests was more in line with the quarter-million-year-old date found from the camel bone sample than the 22,000-year-old more “politically correct” date advocated by Cynthia Irwin-Williams.
There were two other dating methods that were applied at Hueyatlaco. One looked at the volcanic ash deposits again and was called tephra hydration dating. The other method involved studying the mineral weathering to determine the age of the artifacts uncovered at the site. All 4 dating methods, which all concluded that the site was almost a quarter of a million years old, were explained and explored by Virginia Steen-McIntyre in a 1981 publication in the journal Quaternary Research titled “Geological Evidence for Age of Deposits at Hueyatlaco Archeological Site, Valesquillo, Mexico.” The article was subject to a ferocious backlash even from Cynthia Irwin-Williams, the original excavator, who wrote a rebuttal to the article. People in mainstream science shunned Steen-McIntyre for her challenging of the orthodoxy and she was the object of intense derision and harassment. In an open letter to Quaternary Research, Steen-McIntyre wrote:
“Not being an anthropologist, I didn’t realize how deeply woven into our thought the current theory of human evolution has become. Our work at Hueyatlaco has been rejected by most archaeologists because it contradicts that theory. Period.”
Critics who were not just attacking Steen-McIntyre’s character criticized the findings as being contaminated, or that the sedimentary and rock strata were disturbed by animals or floods. Of course, many others alleged that the artifacts were planted or that the dating results were simply faked.
What we may have here is a process of knowledge filtration that occurs in most scientific fields. You have people with egos and reputations and lifetimes of work based on the orthodoxy. Things that conform to accepted ideas will pass through the knowledge filter with no problem. If something comes along to challenge the existing belief in a radical way, it is rejected, even if facts and data are there to support the radical claim. The idea of science with testable hypotheses and data examination is a great thing when applied in its purest form, but most scientists do not admit to themselves and others that there is an “old guard” mentality at work in most scientific fields that seeks to preserve the status quo. Most of the work at Hueyatlaco has not been accepted because it never gets past this knowledge filtration process. The guardians of the textbooks and mainstream science publications will not let this story go to print.
There has been recent work at Hueyatlaco and at other sites in Mexico that challenge the scientific orthodoxy and push back the idea of human habitation in that country to the Pleistocene Epoch, and well past the 12,000 BC date that has been generally accepted. The carved bone and hearths at the El Cedral site in the Mexican state of San Luís Potosí have been dated as being 30,000 years old. The Babisuri Rock shelter on the Island of Espiritu Santo off the coast of Baja California has been dated as having been inhabited 40,000 years ago. There are 4 other sites with older dates including what’s been called the Xalnene Tuff formation where human footprints have been found alongside tracks of extinct animal species. These footprints and tracks were made in the fresh field of ash from an active volcano and the site is located in the same valley as Hueyatlaco near a small ranch called Rancho Xalnene. These footprints have been dismissed as indentations made by pickaxes from an old mining operation. The tuff formation has been dated by one researcher as going back 40,000 years. Another researcher using the argon form of dating claims that the ash fell and the footprints were made over 1.3 million years ago.
So, given these “anomalous” dates at various sites across Mexico – the Hueyatlaco excavation the most famous among them – what are we to make of the early human history of Mexico and the peopling of the Americas in general? Are these seemingly exaggerated dates pieces of an elaborate hoax, are they well-intentioned errors, or do they give us pause and make us reconsider the pre-existing theories of human evolution and migration? As with every topic discussed on Mexico Unexplained, it is up to you, the listener to do further research and to come up with your own well-reasoned conclusions.
REFERENCES USED (This is not a formal bibliography)
Forbidden Archeology by Michael Cremo and Richard L. Thompson
The Hidden History of the Human Race by Michael Cremo and Richard L. Thompson
“Suppressed Evidence for Ancient Man in Mexico” by Virginia Steen-McIntyre, in the August-September 1998 issue of Nexus magazine
“Valsequillo Pleistocene Archaeology and Dating: Ongoing Controversy in Central Mexico” by Silvia Gonzalez, David Huddart and Bennett Matthew, in the 2006 38th volume of World Archaeology.
Link to Dr. Virginia Steen-McIntyre’s organization: http://pleistocenecoalition.com/