That Clovis Overkill Hypothesis? How much evidence is there for it, really?

I am amazed that this Clovis as mammoth murderer to extinction idea still has traction.

I am presenting this here not to convince the reader, but to show that the popular idea of humans as mammoth “extinction machines” has another, valid, side to it.  I was not looking for this article or anything along these lines at the time I found it (a couple of months ago) – but it blew me away, that two BIG names in this area of research (Grayson and Meltzer) had such a paper out there.  In my opinion, this paper eviscerates the Overkill hypothesis.  See what you think:

See “A requiem for North American overkill” Grayson and Meltzer 2003. (Yes, the very same Meltzer who is a co-author on some of the YDB skeptical papers.) All the quotes are from that paper.

The argument that human hunters were responsible for the extinction of a wide variety of large Pleistocene mammals emerged in western Europe during the 1860s, alongside the recognition that people had coexisted with those mammals. Today, the overkill position is rejected for western Europe but lives on in Australia and North America. The survival of this hypothesis is due almost entirely to Paul Martin, the architect of the first detailed version of it. In North America, archaeologists and paleontologists whose work focuses on the late Pleistocene routinely reject Martin’s position for two prime reasons: there is virtually no evidence that supports it, and there is a remarkably broad set of evidence that strongly suggests that it is wrong. In response, Martin asserts that the overkill model predicts a lack of supporting evidence, thus turning the absence of empirical support into support for his beliefs. We suggest that this feature of the overkill position removes the hypothesis from the realm of science and places it squarely in the realm of faith. One may or may not believe in the overkill position, but one should not confuse it with a scientific hypothesis about the nature of the North American past.

They discuss island versus continental extinctions and causes.  And they argue efficiently that projecting island extinctions onto continents – which is VERY commonly done – is a completely wrong extrapolation:

The initial human colonization of island after island was followed by vertebrate extinction. That this premise is true, however, does not mean that it is relevant to continental extinctions. After all, the factors that make islands prone to vertebrate extinction — small population sizes of resident vertebrates, the lack of a ready source of conspecific colonizers, and so on — do not apply to the continental setting.

It is not enough to blame humans for mammoth and mastodon extinctions. Over 30 other species went extinct at virtually the same time – with the lack of evidence of Clovis killing them being non-existent:

How many of those genera can be shown to have been human prey during Clovis times?  The answer is two – mammoth and mastodon—(Table 2) and there are only 14 sites that securely document this relationship [39].  As has long been known [42], this is not a sampling fluke (see Fig. 1). There are more late Pleistocene occurrences of horse than there are of mammoth or mastodon, and nearly as many for camel as for mastodon, yet there are no demonstrable kill sites for horse or camel or for any of the remaining genera [30,31,34,36,37,39]. This is not for want of looking.  Given the high archaeological visibility of the remains of extinct Pleistocene mammals, and their great interest to archaeologists and Quaternary paleontologists alike, if such sites were out there, they would surely be found. Indeed, there is a strong bias in the Clovis archaeological record toward just such sites…

So, the next time you see an “artist’s rendition” like this, think about what you are reading today:

The Extinct Late Pleistocene Mammals of North America

Genus / Common name
Pampatheriuma / Southern Pampathere
Holmesina / Northern Pampathere
Glyptotherium / Simpson’s / Glyptodont
Megalonyx / Jefferson’s Ground Sloth
Eremotherium / Rusconi’s Ground Sloth
Nothrotheriops / Shasta Ground Sloth
Glossotheriumc / Harlan’s Ground Sloth
Brachyprotoma / Short-faced Skunk
Cuonb / Dhole
Tremarctos / Florida Cave Bear
Arctodus / Giant Short-faced Bear
Smilodon / Sabertooth Cat
Homotherium / Scimitar Cat
Miracinonyx / American Cheetah
Castoroides / Giant Beaver
Hydrochoerus / Holmes’s Capybara
Neochoerus / Pinckney’s Capybara
Aztlanolagus / Aztlan Rabbit
Equus / Horse
Tapirus / Tapirs
Mylohyus / Long-nosed Peccary
Platygonus / Flat-headed Peccary
Camelops / Yesterday’s Camel
Hemiauchenia / Large-headed Llama
Palaeolama / Stout-legged Llama
Navahoceros / Mountain Deer
Cervalces / Stag-Moose
Capromeryx / Diminutive Pronghorn
Tetrameryx / Shuler’s Pronghorn
Stockoceros / Stock’s Pronghorn
Saigab / Saiga
Euceratherium / Shrub Ox
Bootherium / Harlan’s Musk Ox
Mammut / American Mastodon (2)
Mammuthus / Mammoth (12)


Only the ones in red have confirmed kill sites (number of sites).  See Clovis hunting and large mammal extinction: a critical review of the evidence (Grayson and Meltzer 2002) .  Also see How Many Elephant Kills are 14? Clovis and Mastodon Kills in Context (Surovell and Waguespack 2008).

The experts in the field don’t sign on to the idea, to their credit (but how about the rest of us and the rest of scientists?) :

Martin has recently noted that “archaeologists have always washed their hands of human complicity in large [mammal] extinction” in North America [78, p. 17], and he is right.  He might also have added that vertebrate paleontologists who specialize in late Pleistocene North America have also cleansed themselves of this notion [28,41]. The reason is straightforward. There is no evidence for it and much against it. While Martin claims that a lack of evidence provides strong support for his position, others have different expectations of the empirical record…

…Our point is simple. The North American version of the overkill hypothesis lives on not because of archaeologists and paleontologists who are expert in the area, but because it keeps getting repeated by those who are not.  As to why it remains popular in those circles, there are likely several reasons, but one seems especially compelling….

….We are not suggesting that the overkill argument emerged as an integral part of the environmental movement; after all, Martin first raised the idea a decade earlier, and overkill models emerged in mid-19th century England in a very different historical context.  Instead, we suggest that the overkill argument captured the popular imagination during a time of intense concern over our species’ destructive behavior toward life on earth.  It retains that grasp today…

…It is easy to show that overkill’s continued popularity is closely related to the political uses to which it can be put.

But popular imagination is not science.

For these discussions, and others like them, overkill provides powerful political capital. That we may agree with the political goals of these authors is immaterial. Our concern here is that both science and environmental concerns are being done a disservice by relying on claims that have virtually no empirical support. We are not suggesting that those who use overkill in this way do so in disregard of the facts against it. We do believe, however, that they are insufficiently familiar with the archaeological and paleontological records bearing on overkill…

In fact, Martin’s recent writings suggest to us that he is no longer trying to approach this issue within a scientific framework. As we have noted, he explicitly maintains that the North American overkill position does not require supporting evidence. He is unconcerned that archaeologists ‘wash their hands’ of his ideas. He criticizes the search for pre-Clovis sites in the New World as “something less than serious science, akin to the ever popular search for ‘Big Foot’ or the ‘Loch Ness Monster’” [58, p. 278]. As one of us has observed elsewhere, Martin’s position has become a faith-based policy statement rather than a scientific statement about the past, an overkill credo rather than an overkill hypothesis…

So, what we have is the father of the overkill hypothesis (Martin) being confronted with the massive lack of evidence supporting it and then saying to the world, “TO HELL WITH EVIDENCE!” and then using ridicule against evidence that weakens his hypothesis.

As I’ve said so many times here, that isn’t science. It is advocacy. It is crusading. And WTF does a crusade have to do with science?

I am blown away by the fact that these two authors felt it necessary to mention in their paper all of the politics. If this much came out of that closet, one has to wonder about what degree of disagreement is going on behind academic doors.


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