A claim is being made, in a recent issue of Nature Magazine, that humans were active in the vicinity of San Diego well over 100,000 years before archaeologists think humans were even in the New World. Most commentary on this claim dismisses it out of hand, but out of hand rejections are no better than foundationless assertions. Let's take a closer look at the Cerutti Mastodon Site. But first, some important context.

The Near Consensus on North American Prehistory

The Clovis Culture is a Native American phenomenon that occurred between about 12 and 10 thousand years ago (most likely between 11,500 and 11,000 uncalibrated radiocarbon years before present).

The key feature of Clovis is the rather extraordinary "Clovis Point." There is another, similar looking, point that goes with the Folsom Culture, which is about as old as the Clovis culture, but a bit younger, and there are a couple of other less common named forms. We refer to them all as "fluted points."

Unlike some other so-called "projectile points" (many of which are knives or spearheads, many perhaps not even mounted in use) fluted points are rarely found in large numbers anywhere, but are represented over a very large region; They are found across the United Sates and Canada, and as far south as Venezuela.

There is almost no evidence suggesting that any humans existed in North America prior to Clovis times, and this has been known for years. Therefore, "Clovis culture" or more broadly, "Paleoindian" culture has long been thought to represent the first humans to come to North America. Since Native Americans physically resemble East Asians (an observation supported and refined by genetic analysis) it has always been assumed that Native Americans came from Asia as Paleoindians, or developed the Paleoindian culture right after arriving in North America. The dates of Clovis sites cluster into such a tight time frame that it makes sense to assume that these folks arrived on an unoccupied continent, spread quickly over a large area, and subsequently differentiated into diverse groups.

The idea of earlier, pre-Clovis, occupation has long been considered by the occasional daring archaeologist, and even the famous African archaeologist, Louis Leakey, suggested that certain finds in the vicinity of modern day San Diego represented much older human occupation. However, North American archaeologists remained firm on the idea that there is no pre-Clovis, and argued strongly and vociferously against the idea. Indeed, any archaeologist who wished to argue for pre-Clovis risked something close to professional censure, others were so sure about Clovis first.

For a very long time it has been at first quietly, and later less quietly, recognized that there are some problems with the Clovis-First hypotheses. First, even though one might expect the early dates for Clovis, if it represented a sudden and rapid colonization of a world with no humans, to be difficult to interpret, it became apparent that the earliest Clovis is in the far East of the continent, with later clovis being farther west. Recent interpretations of the data have suggested that this may not be true, but those interpretations are tenuous. Oddly, pretty solid dating evidence showing east coast Clovis to be earlier was always rejected as unimportant, while a much less clear argument that Clovis out west is early has been quickly and not very critically accepted, presumably because it fits the underlying assumptions of a sudden colonization from Asia.

Fluted points are way more common in the East, east of the Mississippi, in various Mississippi drainage valleys, and along the East Coast. They are relatively sparse in the west, say, on the west side of the Rocky Mountains, and they are very rare in Alaska. So, the distribution of fluted points is exactly the opposite of what one might expect with a simple model of Asians arriving in North America, suddenly becoming Clovis, then spreading from there.

Of the fluted points found in North America, the oldest style, Clovis, is mainly an Eastern phenomenon, with later styles, such as Folsom, are more in the West. If the so-called spatio-temporal boundaries of these styles is correct, and Clovis is older than Folsem, then it is very hard to argue that Clovis is a primary phenomenon that came out of Asia as the first thing people did in North America.

These observations together with the absence of Paleoindian culture in Asia strongly suggests that the actual history of people in North America prior to about 10,000 years ago was a little more complex than the usual textbook version. Indeed, Clovis would make a lot more sense if there was a pre-Clovis culture that did some or much of the initial spreading, followed quickly by the rise of a Clovis Culture among those people, perhaps in the east, which then spread across the continents very quickly. That would have simply been an early example of a phenomenon we see again and again in New World prehistory, where a material phenomenon of some kind, a type of projectile point, or a symbolic image, or something, spreads in what seems like an instant across a vast area.

Beginning mainly in the 1980s, a number of archaeological sites were discovered and presented as pre-Clovis. These are dated using various means. They occur across the US in Pennsylvania, Souoth Carolina, Oregon, Florida, Alaska, and elsewhere. They are also found in South America in Brazil, Chile, and Columbia. Most, perhaps all, of these sites -- there are about 16 of them -- are very strongly and forcefully argued to be real, and have varying degrees of evidence on them.

Most of the sites date to either just a thousand or two years, or sometime, just centuries, before Clovis and would easily fit into a pre-Clovis model as suggested above. This would go with the idea that somehow, humans arrived in North America, spread out, then popped out Clovis Culture soon after. Some of the sites are much earlier, but as far as I know, all the earliest sites have very questionable artifacts or dating that is not very secure.

I am not certain, but I think most of the North American archaeologists who so forcefully argued against pre-Clovis of any form have either moved off that position, stopped talking, or died off. Now, I believe, most North American archaeologists accept that there is a distinct possibility that there is what I would call a "near-Pre-Clovis." But, since there are just over one dozen sites across two continents, one must be reserved in assuming this. Such a small number of sites could represent a small number of aberrant if well meaning interpretations of sites that have something wrong with them. I personally have excavated many, many archaeological sites, and I have seen things that can't be explained. Personally, I think some of the late pre-Clovis sites are good. But, I would not be surprised if an all knowing alien with a time machine landed nearby and proved that I was wrong.

The CM Mastodon Site: Humans in the New World at 130,000 years?

The Cerutti Mastodon site is in San Diego County, California. The site was excavating in the early 1990s by a team from the San Diego Museum of Natural History. If you ever get a chance to visit that museum, do so. It is one of the many museums of Balboa Park, which also includes the famous San Diego Zoo.

The finds at this site include a juvenile Mastodon, Mammut Americanum, as well as dire wolf, horse, ground sloth, camel, and mammoth.

The site is dated using Uranium-thorium dating on the mastodon bone, to 130,000 +/- 9,400 years b.p.

A recent analysis of the site, just published in the journal Nature, claims that the bones show evidence of human modification, and that some stones also found on the site show evidence of having been used to modify the bones.

The modification suggested is the smashing of bone to extract marrow, and possibly, to make some flakes or otherwise modify the bone to make tools.

The authors of the paper suggest that there are, as commonly agreed by North American archaeologists, four criteria that a site must meet to be considered a candidate for early pre-Clovis human evidence:

1) archaeological evidence is found in a clearly defined and undisturbed geologic context;

2) age is determined by reliable radiometric dating;

3) multiple lines of evidence from interdisciplinary studies provide consistent results; and

4) unquestionable artefacts are found in primary context

They argue that all of these are met. From the abstract:

The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. 230Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production. Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa, Eurasia, and North America. The CM site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas.

That the site is in a good geological context is apparently beyond question, as far as I know. The "refitting" referred to is where bits and pieces of one thing that was broken apart can be glued back together, showing that since the breaking event not much has moved around, which helps to argue that the site is not too messed up by geological processes. The dating seems good. Everything seems good.

Yay, an early site showing humans in North America way before we ever thought!

But wait, not so fast ...

Why this site could be real, and other comments on the early Americas

Archaeologists have a conceptual problem with discontinuity. They don't believe in it.

Say you are working in a previously unstudied part of the world (there are none, but pretend). You find a site with some pottery on it, and date the site to 1,000 years ago. In the same area, you find several sites, of various dates, from 1,000 years ago to 4,000 years ago, but they are all sites with chipped stone tools on them and no pottery. But then, you finally find another pottery bearing site. The pottery looks different, and the site was fairly deep down, so when you get your dates back from the lab and they are about 4,000 years old, you are not surprised.

And, now, you know that pottery using people lived here from 4,000 years ago to 1,000 years ago, right?

Wrong. It is possible that people showed up here with pottery, and left, leaving behind non-pottery using people, then came back later. Or, people moved here with pottery, or invented or were introduced to pottery, 4,000 years ago, then stopped using it for some reason, then pottery made a return, somehow, more recently. The problem is, most archaeologists will not accept that once something happens, it can unhappen, even though we actually do know of places in the world where pottery was brought there with the first people, then forgotten about or rejected for some reason, later.

So, here's the idea. During warm periods, like the interglacial of roughly the age of the CM site, and the present, hominins tend to spread. Even the ones that like warmer regions, maybe not even humans, spread around during warm periods, and spread north. So, naturally, some of them get to the New World somehow, and these are them. They don't even have to be chipped stone tool using humans. They could be bone breakers. They could be bigfoot! They could be anything.

Now, this may seem like a crazy idea, and it almost certainly is. But, the rejection of occupation as early as 130,000 years ago because we have no evidence of anything half that old requires that the new world can be occupied in only one way: something or someone shows up, then they never leave. This is in direct conflict with the known migrations of large mammals, many of which migrated either to the New World from the Old World, or the other way round, several times over that last 5 or more million years, and most of which do not exist in the place they migrated to now.

Why the Old World makes the CM site highly unlikely

I know an archaeologist who once said this. She said, teaching her class, that the discovery of a house structure at about 5,000 years ago (by the way, it might have been the house structure I discovered, which for a time was the oldest one in North America) tells us that by 5,000 years ago, Native Americans had a concept of building a house, like a wigwam, and the technology to do so. I once read an archaeological monograph that suggested that the presence in some 3,000 year old pottery of impressions of woven material show that by that time Native Americans could weave cloth. One textbook refers to the earliest fire in North America (several thousands of years back) indicating that we now knew that by that time, at least, Native Americans had fire and thus could possibly cook their food.

I've read and heard North American archaeologists say things like this over and over again. These statements assume that the first proto-Native American people to come to the new world, say as just-pre-Clovis people, must have arrived naked and technology free!

People in the Old World had chipped stone technology, whereby stones were used to break stones in a very systematic (and not too easy to learn) way to produce, ultimately, tools. Our ancestors had this technology before the genus Homo existed. In fact, it may be the case that our ancestors were stone tool chipping bipedal apes for as long before the rise of the genus Homo as after (this remains to be pinned down). Modern humans have existed on this planet for only a fraction of the time that hominins were making chipped stone tools. Until the abrupt and dramatic near perfect elimination of chipped stone technology in recent centuries, chipped stone tool technology was as much a part of human behavior and culture as walking on two legs was.

We know this because of all that Old World archaeology that has been done. Despite the limited understanding of world prehistory by many North American archaeologists, the truth is that a human (even a non-fully modern human) presence in the New World would have chipped stone tools with it.

If a creature was at the CM site with a culture that lacked chipped stone tools, but that used hammer and anvil stones to break up bone, it was an ape, not a hominin. It was Gigantopithecus, or something. Bigfoot! CM is potentially believable as a site if it occurred in a larger time horizon with definitive human evidence. In other words, a bunch of chomped up elephant bones down the way from clear unambiguous human occupation on a landscape with many sites of that date might be acceptable as a human site, but not this. Not just pounded bones with no other cultural manifestations.

Now, I want to add new rules to the ones listed above.

5) The artifacts have to include evidence of proper chipped stone tool technology, as this is a ubiquitous trait of Homo and proto-Homo

6) Among the chipped stone, there must be both flakes and pieces that are flaked, because many natural processes will produce one or the other (usually flaked pieces) without human engagement.

7) The flakes must exhibit many cases of clear striking platforms, the part where the flake is hit to make it fly off the parent rock, and those striking platforms must be mostly below 90 degrees angle, because that is the experimentally established difference between "natural" flakes (including those made by cars running over rocks and rocks falling off cliffs, etc.) and human made proper flakes.

8) If flaked bone is invoked as an artifact type, the flakes must be numerous and have the same low angle of percussion, and there must as noted above, also be stone flakes.

This is the underlying fact that must be understood by people considering the CM site as human. Humans bust up bones, but busted up bones in the absence of any other evidence of human activity does not constitute unquestionable artifactual nature. Ever.

Just to make sure that I was still up to date on bone breakage taphonomy, the study of how to interpret bone breakage, I asked Professor Martha Tappen of the University of Minnesota, a bone taphonomist, for her opinion about the site. She told me, "I would say that the breaks appear to be consistent with human breakage, but quite possibly other causes, too, such as backhoes and perhaps other scenarios involving trampling. Other evidence is needed to support the idea that people reached the new world at this early time."

What really happened at CM

I spent a certain amount of time living among the elephants of the African Rain Forest. Well, OK, I wan't actually "living among them" but I was living there doing archaeology and other things, and they were there too. In fact, I studied elephant movement and trial making, and in so doing, observed a lot of places where elephants tromp around.

Some of the elephants we observed in the Ituri (along with the afore mentioned Professor Tappen) which had been killed over the years by Efe hunters (they are the traditional elephant hunters of the region), died on or near regular elephant trails. Once an elephant is all butchered up or scavenged, I assume the living elephants walk around the remains, though in some areas they have been known to play around with the bones of the dead. But eventually, the bones get incorporated with the undergrowth and the sediment, and get trampled by the elephants. The elephants also trample rocks. I saw locations where the elephants walked a lot, including trails and one location where they had dug a cave to obtain sediment that they would eat, where there was so much elephant trampling of stone that most of the stone looked human modified.

CM site has several animals, including some large ones. Something about this site attracted animals that then died, but at one point were alive. This is a very common phenomenon in paleontology, and is not fully understood. It is very likely that the broken up bones and the seemingly modified stones look the way they do because huge multi-ton animals stepped on them repeatedly.

But what if ...

I don't want to rule out CM out of hand. I don't want to do this because Archaeology is full of stuff that was ruled out by orthodoxy then later found out to be important or real, but data was lost because of the narrow mindedness of the narrow minded. I believe it is appropriate and necessary to reserve a part of our dogma for possibilities, evidence for things that we are pretty sure are not real but that have just enough credibility, just enough of a question, to allow for a later surprise. I would love to see more large mammal sites of the late Pleistocene excavated carefully to see what they look like. A program of exploration for and investigation of sites during and near the Last Glacial Maximum in the Western US is a good idea, and should yield some very interesting paleontological results. If there was some kind of a hominin running around then -- which is very unlikely and indeed almost impossible to imagine -- but if there was one, it would eventually be bumped into. Meanwhile, think of all the cool extinct animal stuff we would get to learn no matter what the human prehistoric story turns out to be!