Mar 28 2011

A Pre-Clovis Find?

I love scientific mysteries of all kinds – ones where competent experts can legitimately disagree on the interpretation of the evidence, and all agree on what evidence would most likely settle the debate. It’s like a cliffhanger of a great mystery series, except you don’t know when the new season will begin. You just have to wait for new episodes to pop up unexpectedly.

One such debate is the question of how and when were the Americas peopled. This is a story of our recent pre-history. Knowledge of this time has not survived to the present, so we have to reconstruct the past from the clues left behind. And it is recent enough in the past that there is likely to be good physical evidence for archaeologists to find.

For a time the Clovis culture was considered to be the first people in the Americas. They likely crossed the land bridge from Asia to North America about 13,500 years ago, and then worked their way down to South America. They are called the Clovis culture because they are defined by the artifacts they left behind – their projectile points have a very distinctive feature that defines the Clovis. They are fluted at the base on both sides – the stone is precisely carved to be made thinner at the base to allow for better hafting to a wooden spear. These points were designed to hunt the large game of North America, like mammoths. Wherever Clovis points are found – you have Clovis culture.

Unfortunately, there are no sites that have both human remains and Clovis points, so we cannot be sure about the genetic heritage of the people responsible for the Clovis culture. This is definitely a site, somewhere out there, waiting to be found. It is possible that the Clovis culture was not the product of a single population of humans, but was in reality a culture that could have spread to different populations. In other words – Clovis may track a technology, but not a specific people. This is an intriguing idea that also makes it all the more important that we find human remains and Clovis points together.

In any case, there were people widely distributed in the Americas from 13,500 to about 11,000 years ago using Clovis technology. This technology then disappears and is replaced by later paleo-Indian cultures. Another mystery is what, exactly, happened to the people using Clovis technology. Did they die out and were replaced by later migrations? Did they become the later cultures, or merge with them? Perhaps they simply changed their tools after the extinction of much of the megafauna of North America, switching to points better suited to smaller game.

Another question is whether or not the Clovis culture truly represents the first people in the Americas. Is there any evidence of a pre-Clovis culture? Now a new find adds potentially significant evidence to the claim that there were pre-Clovis people in the Americas.

A large find of stone tools and evidence of tool crafting was found north of Austin, Texas – over 15,000 individual pieces of stone. They are largely small tools, which has led archaeologists to suspect that this was a mobile assemblage – made to be picked up and carried. Most importantly, the tools date to about 15,000 years ago, a full 1,500 years or more before the earliest Clovis culture.

In addition to the dating, the find is located beneath a later Clovis site. If the arrangement of these finds represents that order in which they were deposited (and not later mixing) then the tools farther down must be older than the Clovis points found further up.

That is the straightforward interpretation of the find, and by all accounts the authors did a thorough job of presenting their data. Of course, the interpretation of this evidence is not without its controversy also. Other scientists have done their job by thinking of all the possible weaknesses in the evidence.

According to interviews done by the BBC it has been pointed out that the dating method used, optically stimulated luminescence (OSL), while considered a reliable dating method may not be as accurate as carbon dating. If the dates are off by a couple thousand years then this would not be a pre-Clovis find.

Further the assigning of the tools from the two layers to Clovis and non-Clovis can be questioned on the basis that neither contains the projectile points that are diagnostic of the Clovis culture – they contain only other kinds of stone tools.

Perhaps most problematic is that the tools were found in a flood plain. They are buried in clay, which is a good thing in that the clay is hard and not easily disturbed. So from that point of view there was probably not later mixing of the dirt layers. But the clay also indicates that these tools may have been deposited in their current location from somewhere else by flood waters. If the tools were moved around by water, then their relative positions may be deceptive.

While this is clearly an important find, scientists will need to carefully examine the evidence and explore alternate theories before we can know what the definitive answer is.

From reading the article and interviews I was also left a bit confused as to the current status of the theory of a pre-Clovis population in the Americas. From my discussions with archaeologists it seemed to me that the pre-Clovis theory was speculative and not confirmed. However, some of the archaeologists interviewed for the BBC report indicate that the “Clovis-first” hypothesis is dead, and that other sites already clearly establish the existence of pre-Clovis people in the Americas.

I often find it challenging to find out what the consensus is within a specialized field – it seems like you will get a different picture depending on which experts you talk to. What is clear is that there remain two schools of thought regarding pre-Clovis people in the Americas. As an outsider, I am currently unsure which side has the upper hand, in terms of evidence and consensus.

It does seem likely, given how testable the claims of each side are, that eventually opinion will yield to more definitive evidence.

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