Upper Paleolithic

Is there anything surprising about finding the Cambridge Reference Sequence in Paglicci 23?

UPDATE follows at the bottom.

If you have a subscription to Nature, you can get a short story from last week's issue, which explores the reaction of a couple of genetics-types to finding Neandertal genes responsible for human mental abilities:

That has to be interbreeding. The earlier studies had missed it because they hadn't considered the changing impact of natural selection over time."

"You can back that up?"

"Absolutely." Beth was always meticulous about her data.

I didn't have to force a smile. "That's fascinating," I said. "It will make Nature for sure." It would get a lot of people hot under their collective collars, but that was fine. Evidence of interbreeding with Neanderthals would create a new paradigm for hybridization being behind the rapid advance of modern humans and make me famous. "What genes are involved?"

Notice: you can tell this is fiction because the result "will make Nature for sure"!

On the other hand, some parts are uncomfortably true-to-life:

"I'm a scientist. I want to know the truth!" More importantly, I wanted to finish the contract; that was my job as principal investigator. I'd always succeeded before; that was why after two decades at the university I was department chair and Beth was still a research assistant.

Yes, the plucky female scientist who believes in the Neandertals is passed over for advancement, while the overbearing man who cares only about grant applications runs the whole department. Well, try to tell me that part is fictional!

It's not that great a story, but the surprise conclusion is exactly what we've been writing -- some aspects of today's human brain biology probably reflect the genetic interactions between Pleistocene human populations. It's neither shocking nor surprising. It's simply evolution!

References:

Hecht J. 2008. The Neanderthal correlation. Nature 453:562. doi:10.1038/453562a

Science's Michael Balter reviews the recent Cambridge conference on "Global Origins and Development of Seafaring". The article begins with a suggestion that the first inhabitants of Flores floated there on vegetation rafts by accident -- channel crossings being otherwise impossible for Lower Paleolithic hominids:

"Flores is the exception that proves the rule in terms of when seafaring really began," says Atholl Anderson, a prehistorian at the Australian National University (ANU) in Canberra. [Jon] Erlandson agrees: "Otherwise, H. erectus should have colonized Australia and the surrounding islands."

It mostly seems to be about Wallacea, Sahul, and Melanesia.

The article features a disagreement concerning the colonization of these regions. Some think that island colonizations started before seafaring technology was quite ready for prime time. In that scenario, the initial habitation of parts of Wallacea along with Australia and New Guinea was a sort of accidental chain of small founding events, possibly as early as 60,000 years ago or earlier.

The opposing viewpoint holds that these islands (and continent) were inhabited relatively late and quite suddenly, by people who had developed an advanced seafaring skill. Balter quotes University of Utah archaeologist Jim O'Connell to good effect:

In the last few years, O'Connell, together with archaeologist Jim Allen of La Trobe University in Bundoora, Australia, has argued from a detailed analysis of radiocarbon dates for a "short chronology" that puts the occupation of Sahul no earlier than about 50,000 years ago. He pointed out that by 45,000 years ago modern humans had colonized a number of islands between Sunda and Sahul, called the Wallacean Archipelago, which stretched at least 1000 kilometers even when sea levels were at their lowest. Reaching many of these islands required sea crossings of 30 to 70 kilometers, sometimes against the currents. Most animals from Asia never achieved these crossings, implying that humans must have used technology to do it. That 5000 years of colonization, O'Connell said, represented a relatively short "archaeological instant."

O'Connell also argues that some of the island sites before 40,000 years ago include deep-water fish, suggesting relatively advanced ocean-going boats at that time -- something I noted in a post on the East Timor site, Jerimalai.

Which side is right? I don't know, but it's good that they are formulating hypotheses this way, involving the technological trajectory, genetic constraints on small populations, and various ecological parameters.

References:

Balter M. 2007. In search of the world's most ancient mariners. Science 318:388-389. doi:10.1126/science.318.5849.388

Der Spiegel reports on recent portable art finds at Vogelherd, Germany:

The figure of the woolly mammoth is tiny, measuring just 3.7 cm long and weighing a mere 7.5 grams, and displays skilfully detailed carvings. It is unique in its slim form, pointed tail, powerful legs and dynamically arched trunk. It is decorated with six short incisions, and the soles of the pachyderm's feet show a crosshatch pattern. The miniature lion is 5.6 cm long, has a extended torso and outstretched neck. It is decorated with approximately 30 finely incised crosses on its spine.

Nick Conard at Tübingen is quoted; he's the responsible archaeologist. The story is on occasion of the mammoth and other artifacts going on display at a museum exhibit. They are dated Aurignacian, which makes them among the earliest examples of figurative art in Europe.

It's likely that these include the figurines that Conard was presenting in 2003, as reported by Rex Dalton, although a mammoth was not mentioned at the time. A series of portable art figures were discovered at Vogelherd by Gustav Riek, who excavated the cave in 1931. Several of these are housed at the Museum Schloss Hohentübingen, including another mammoth. Conard (2003), in his description of portable art from Hohle Fels, includes a table listing 10 figurines from Vogelherd, all found in the original excavation by Riek.

Conard and colleagues (2003) reported on the radiocarbon chronology of the Aurignacian at Vogelherd, finding a range of AMS dates between around 29,000 and 36,000 radiocarbon years, with most dates clustering between 30,000 and 31,000. Figurines from other caves in the region date to the same age range, including those from Hohle Fels, Geissenklüsterle, and the Löwenmensch, or "Lion-man" from Hohlenstein-Stadel. This area preserves an exceptional sample of early Aurignacian art objects.

References:

Conard NJ. 2003. Palaeolithic ivory sculptures from southwestern Germany and the origins of figurative art. Nature 426:830-832. doi:10.1038/nature02186

James Adovasio, Olga Soffer and Jake Page have a new book entitled, The Invisible Sex: Uncovering the True Roles of Women in Prehistory. The authors are well-known for their work in both New World and Old World archaeology. In particular, the joint work by Adovasio and Soffer has uncovered evidence for the earliest fabrics and fiber technology, and has led to new interpretations for the famous "Venus" figurines from the European Upper Paleolithic.

I ran across a nice long review of the book by Laura Miller at Salon.com. It's free if you watch their ads, and the review is full of clever observations. Here's a sample:

Their point is that, like Hollywood action films, many early conceptions of prehistoric life were fantasies, the work of anthropologists caught up in a thrillingly macho vision of our forebears that owes more to Conan the Barbarian than to the archaeological record. That vision rarely featured women, and when they did appear it was only to sit around awaiting the next delivery of mammoth steaks, for which, it was implied, they would trade their sexual favors or perhaps the handful of nuts and berries they'd rustled up on the side. So seductive is this "theme of man the hunter" that it prevailed when the remains of a diminutive new species of the genus Homo were discovered on the Indonesian island of Flores in 2004 (and promptly labeled "hobbits" by the press). An artist's drawing of the creature depicted it as bearded fellow holding a spear and carrying a freshly slain giant rat slung over his shoulder -- despite the fact that the chief find was a female.

The review notes that the book also covers the anatomical constraints of the birth process in humans and their implications for cultural assistance with birth -- that's drawn from work by Karen Rosenberg and Wenda Trevathan (quick summary here) -- and I happened to have lectured about it today. It's very important stuff in terms of human life history strategies, and it is likely tied in with the evolution of the human brain. So anatomically speaking, women are central!

I hope to write more about this book when I get a chance to read it -- Soffer and Adovasio have been really important in reframing our understanding of sex roles in the past, and this looks like an interesting contribution.

John Hoffecker, one of the authors of the Science paper by Anikovich et al., wrote a consideration of some of the points in my two posts of last week (here, and here).

Hoffecker suggests that the Strelets assemblages (the ones with Middle Paleolithic elements) are unlikely to have been produced by Neandertals, both because they persist until relatively recently, and because they are found at much higher latitudes than Kostenki, for example at Mamontovaya Kurya. I have some quite contrasting e-mail from a long-time correspondent, who offers that the Strelets assemblages are quite comparable to Szeletian, generally considered to be a Neandertal-produced "transitional" industry, and there is no diagnostic skeletal evidence to suggest these tools were not Neandertal-manufactured.

Personally, I would observe that there may be no predictive reality to the Neandertal-modern distinction, certainly not within this post 45,000-year timeframe. Genetics now provides good evidence that living humans descend from an ancient structured population with a significant fraction of Eurasian members. It is of course possible that some (or even all) European Neandertals still became extinct without issue -- the genes do not have "Neandertal" stamped on them. But the fossil evidence certainly supports the hypothesis that the "Upper Paleolithic revolution" in Europe involved some (i.e., enough to be visible) population mixture.

Whatever the genetic relationships of the hominids, there was evidently no information barrier between them capable of preventing the social learning of stone reduction sequences. The "transitional" industries are sufficient to demonstrate this information transmission. To be sure, there is a limit to which we can infer contacts from archaeological assemblages, which represent industries that in some cases lasted for many thousands of years. Just as for the genes, we cannot say whether these exchanges were sporadic or regular, large-scale or small-scale.

What does that mean for Kostenki? I think it means there is no contradiction between a long-term, widespread "transitional" industry and the idea that such industries have origins in the Middle Paleolithic. Both can be true. This implies things about the population of Eastern Europe, in terms of genetics, ecology, and the dynamics of information transfer. Where industries are interleaved at a single geographical location, this may say much about both natural ecology (climate fluctuations) and information ecology (social learning within groups applied to natural problems). The form of population contact is also relevant, but lies at a deeper level -- which technological patterns may or may not be able to address.

Australia's The Age online has a story by Deborah Smith that gives a short report about excavations at Jerimalai rock shelter, East Timor:

A cave site in East Timor where people lived more than 42,000 years ago, eating turtles, tuna and giant rats, was unearthed by Sue O'Connor, head of archaeology and natural history at the Australian National University.

The article discusses the significance in terms of a possible demonstration that the Timor route was taken by early Australian colonists, rather than the northern route via Sulawesi -- although it by no means rules out the northern route.

There is the obligatory mention of nearby Flores:

Although the Jerimalai site is at least 42,000 years old, it could be much older, Dr O'Connor said, because this was the detection limit of the radiocarbon dating method used. She said the simple stone tools unearthed in the shelter were similar to those used by the species of hobbit-sized people who lived in a cave on the nearby island of Flores until 12,000 years ago.

But she was confident Jerimalai's inhabitants were modern humans, Homo sapiens, and not small-brained members of Homo floresiensis, because of the evidence for their sophisticated behaviour found in the dig. Fish such as tuna, for example, "could only have been captured in the deeper waters offshore using hooks, and probably also water craft", she said.

The find, however, raised big questions, such as why modern humans appeared to have bypassed Flores on their way to Timor. One possibility was that the hobbits were able to repel them.

Or, modern humans were on Flores and left their tools there...

Actually, the most important piece of evidence at this Timor site may be the exploitation of deep marine resources, because it really shows a sophistication of seagoing technology. This sophistication is quite consistent with the early habitation of the Bismarck Archipelago before 30,000 years ago.

These people were routinely going far from land in their watercraft. The habitation of these islands was not accomplished by happenstance floating on ersatz rafts; it was part of a systematic exploitation of a marine resource niche.

The relevance of the site for the initial colonization of Sahul depends on its date. At present, the evidence for human habitation of Australia is certainly older than 40,000 years, and apparently younger than 60,000. If humans reached Australia as early as 60,000 years ago, they could easily have filled it by 42,000 years ago. After all, people took only a few thousand years to fill the Americas from top to bottom. So if the site is only 42,000 years old, it might represent a complex seafaring culture that actually followed the first Australian colonists by a substantial degree, and may have played little role in the origins of the Australians.

On the other hand, if the site is much older than 42,000 years, or represents a culture with substantially older time depth, then it might well be closely linked to the first Australians. In which case we could probably infer that the initial habitation of Australia and New Guinea were events that involved a sophisticated and potentially rapid spread along the coasts, with later penetration into the interior.

A sophisticated seafaring modern human culture that dated to as early as 60,000 years would encompass almost all the time depth of the Liang Bua cave stratigraphy, by the way.

I've been buried in archaeology papers the last couple of weeks, and so I thought I would recommend a few real gems. The first on my list is this paper, titled "What is a burin? Typology, technology, and interregional comparison," by Silvia Tomášková.

The paper uses that most elusive of Paleolithic type tools to talk about the problems caused by using typological classifications. There is a lot of detail about manufacturing methods and possible uses in the paper, so it is not light reading.

But it has some good introductory material, including this passage about the Dibble movement:

Since 1980's the stylistic-functional "Mousterian debate" has been diverted in a new direction that stresses use, reduction sequence, and maintenance of lithic artifacts rather than formal tool types (e.g., Barton, 1989, 1991; Coinman and Clausen, 2000; Dibble, 1984, 1987, 1988, 1990, 1995; Hays and Lucas, 2000; Geneste, 1990; Jelinek, 1988; 1991; Knutsson, 1988a, 1988b; Kuhn, 1991, 1992; Lucas, 1999; Rolland, 1981, 1988; Rollefson, 1988; Stiner and Kuhn, 1992). It has been suggested that a number of the classic types in fact represent steps in a reduction sequence, and their variable presence in archaeological collections is a result of different stages of production or reduction. Since the original studies (Dibble, 1984, 1987), numerous archaeologists adopted the "reduction model," applying it across time and space to archaeological materials ranging from Middle Paleolithic to Epi-Paleolithic (e.g., Neeley and Barton, 1994). The underlying premise and conclusion of these studies has been the universality of rational decisions regarding raw materials, whether resource availability, organization of technology, or the relationship to mobility and settlement patterns constituted the primary research focus of the investigator (e.g., Andrefsky, 1994; Bamforth, 1986, 1990; Kuhn, 1994). Yet detailed studies of technological practice suggest that techniques involve cultural choices deeply entrenched in local tradition and history, and that similar problems can give rise to quite different solutions (e.g., Edmonds, 1990; Lechtman, 1977, 1984; Lemonnier, 1986; Riddington, 1982; Schiffer and Skibo, 1997). As Shiffer and Skibo (1997, pp. 27–28) note, formal variability across time and space is no longer explained as a result of stylistic or functional differences but rather as difference in "design," described in terms of technological choices. The idea of technological choice has been successfully adapted in the chaîne opératoire approach that examines the operational sequence of tool creation, use and discard, and has produced some of the most interesting work that circumvents typological debates (e.g., Almeida, 2001; Boeda et al., 1990; Chazan, 2001; Hays and Lucas, 2000; Lemonnier, 1986, 1992; Schiffer, 2001; Schiffer and Skibo, 1997). Recent interest in gender has led to suggestive studies of formal and expedient tools being in some cultural contexts linked to men and women's workspaces (Gero, 1991; Sassaman, 1992) (Tomášková 2005:84).

The paper uses analysis of function and manufacture to conclude that the "burin" is not properly a cultural category; instead "burins" result from several different processes including stages of modification of other tools:

I started this essay by asking: "What is a burin?" On the basis of the above analysis, the simplest answer would be that a burin can be a number of things, a degree of variability obscured within a singular, typological point of view. Taking the category of burin apart leads to a conclusion that any one form may be a result of several actions, and frequently may not represent the final stage. Rather than simply explaining burins, then, this essay contributes to a debate that re-examines the traditional concept of stone tools as discrete, functionally specific forms, finished according to an accepted, culturally predetermined pattern, and used accordingly. Recent work focused on the life histories of artifacts with the aim to understand technological choices is a much welcome development in this direction (e.g., Bleed, 2001; Boeda et al., 1990; Roux, 2003; Schiffer, 2001; Schiffer and Skibo, 1997). Most generally of all, however, this study suggests a need to examine collections as a whole rather than separating individual typological groups from each other, and to consider the contexts in which they were created. Interpretive caution is particularly crucial when we are dealing with inter-regional comparisons, museum collections or data sets constructed at the intersections of different methods and theories than those currently in use.

Of course, considering the "entire assemblage" is credible when the entire assemblage consists of hundreds of artifacts, but as samples get smaller it becomes more and more tempting to use high-frequency type tools as indicators of some sort. Paleolithic archaeology is necessarily wedded to small sample logic, like it or not. Even if we are considering a sample of 200 artifacts, an artifact class that amounts to 10 percent of the sample has only 20 specimens. So if we introduce any variation in manufacture or use among those 20, the entirety of the pattern becomes quite difficult to assess. Bring us down to a sample of 50 artifacts and it is quite impossible.

References:

Tomášková S. 2005. What is a burin? Typology, technology, and interregional comparison. J Archaeol Method Theory 12:79-115. DOI link

I skipped last week's (9/15/2006) Science, and so missed this article by Michael Balter on radiocarbon dating. But some online discussion boards have been talking about it, and this passage especially is worth reading:

Encouraged by their recent successes, radiocarbon researchers now have their eyes on the bigger prize of the 50,000-year limit. Indeed, when the IntCal group began work on the 2004 curve, it had high hopes of extending it back to this final barrier. Yet it was not to be. Although the marine data sets were reasonably consistent with each other up to 26,000 years ago, after that they began to scatter and diverge, in some cases by up to several millennia. Geochronologist Paula Reimer of Queen's University in Belfast, Northern Ireland, who coordinates the working group, says that the differences--among the raw data as well as among the researchers--were just too great: "We had four or five people, all of whom thought their records were right." So the group settled for publishing in Radiocarbon a comparison of the data sets earlier than 26,000 years, which they ironically called "NotCal"--meaning, Reimer and other members say, that it was not intended to be used as a calibration curve.

But archaeologist Paul Mellars of the University of Cambridge in the U.K. used the published data to essentially do just that. Mellars was eager to get the most accurate dates for possibly contemporaneous Neandertal and modern human sites in Europe. So he used the midpoint of the differing "NotCal" curves to approximately calibrate the radiocarbon ages of 19 hominid sites ranging from Israel in the East to Spain in the West. Using this best-guess method, Mellars found that modern humans had not only spread across Europe faster than previously thought, but that they had overlapped with Neandertals during a shorter interval: only about 6000 years rather than 10,000 years in Europe as a whole, and as little as 1000 years in some parts of the continent. Mellars concluded in the 23 February 2006 issue of Nature that Neandertals must have "succumbed much more rapidly to competition" from modern humans than many had assumed.

But Reimer and others say Mellars should not have used the NotCal data as he did. "It is dangerous to draw too fine conclusions using these data sets," says Reimer, because they have not been finalized and the divergences between them have yet to be reconciled. Other researchers have started asking van der Plicht whether they can use the "Mellars curve" for calibration. "This is a bad thing," says van der Plicht.

Mellars insists that archaeologists can't wait for a final calibration curve. "Are we all really expected to keep studies of modern human origins on hold for the next 5 years, until they decide they've finally got the calibration act together?" he asks. The working group, he argues, "has hijacked the term 'calibration' to mean an absolutely agreed, rubber stamped, legalistic, signed, sealed, and delivered curve." And even when the experts agree on a curve, Mellars says, it will not be "final and absolute" but "simply the best estimate from the data at the time."

Now, even something that isn't officially approved by geochronologists might still be correct. So the question is whether errors were introduced by Mellars into the chronology by using the "NotCal" not-calibrated calibration (and yes, the Mellars paper uses without noting the irony "the recent NotCal04 'best estimation' calibration curve").

The problems are noted in a communication to Nature last week (9/14/2006) by Chris Turney, Richard Roberts and Zenobia Jacobs:

Atmospheric ¹⁴C variability has not followed a simple, smooth pattern, as suggested by Mellars. Instead, smoothing took place during the statistical analysis of these data sets to develop the NotCal04 mean best-fit line. By using the mid-point of the mean best-fit line, Mellars artificially improves the apparent precision of calibrated ages in his Fig. 3; even 'infinitely' old ages are reported with improved precision, whereas calibration almost invariably results in age ranges that are significantly larger than the radiocarbon measurement error.

It's a bad sign when your method improves the precision of infinite dates. In fact, you always add to the variance of a measurement when you multiply it by some correction that itself entails measurement error.

But Mellars' central point was not principally about the ages of particular sites, but instead about the total time taken by modern humans to invade Europe. Can we still get an estimate of a reduced time period for this "invasion" if we use the calibrated dates properly?

To answer that, we need to look at two graphs. First, the graph used by Mellars (2006) to support the idea that the total time taken by modern humans to occupy Europe was short:

Radiocarbon dates for sites from West Asia and Europe, Figure 3 of Mellars (2006). Sites numbered as in original text.

You can see in this graph the effect of "calibration", at least according to Mellars -- it reduces the statistical error associated with each date. Indeed, the caption to this figure says:

Owing to the slope of the calibration curves, the error bars ( 1 s.d.) on the calibrated dates are smaller than those on the uncalibrated dates.

A moment's reflection reveals this to be a nonsensical statement. The error bars may be attributable either to measurement error (in the proportion of ¹⁴C) or to calibration error (relating the current proportion to the original atmospheric proportion). But these error estimates are applied to dates in "radiocarbon years" -- meaning that they don't include possible error in the original atmospheric proportion. Indeed, if they did include this error, these error bars would have to stretch to cover the NotCal-produced dates!

But the "slope of the calibration curve" certainly can't reduce error due to measurement in the sample. At best, the current calibration can predict that a given date must represent a slightly larger number of half-lifes than the uncalibrated date, because the original atmospheric proportion of ¹⁴C was higher than today. It can't reduce the standard error due to measurement, and therefore won't reduce the confidence interval on the date as reported in radiocarbon years (it certainly may reduce the total error, which is usually overlooked).

To understand how Mellars came to this erroneous conclusion -- and to see how it affects his assertion regarding the time period of modern human dispersal -- we need to consider the NotCal04 calibration curve itself:

Radiocarbon calibration data, Figure 1 from Turney et al. (2006). I added the pink rectangular regions. The lower pink rectangles represent the low variance on dates drawn from the NotCal correlation region, as apparently Mellars did. The upper, wide, pink rectangles represent the error that might be assigned to the full calibration process, including uncertainties in the underlying calibration data. In other words, they encompass the range of calendar dates that might be attributed to different samples of a single radiocarbon date. This error range does not necessarily include measurement error (except insofar as error on calibration samples is distributed just like error on fossil samples.

OK, you probably read the caption, so you get the gist of this picture and my pink rectangle additions. In short, the width of the NotCal calibration is very narrow, because it is a summary of many data sets. But the dispersion within those original data sets is very high. This means that for any given radiocarbon date, there is actually a very wide interval of possible calibrated dates that it might represent. The range of this dispersion is high partly because it includes dates from different regions and raw materials (here, mostly coral and shells) -- and these are exactly the kinds of problems that create variance in archaeological radiocarbon dates. So we should be looking at wide error bars -- much wider than we are used to doing.

Making this source of error explicit certainly doesn't decrease the error bars of measurements -- it vastly increases the error bars. This is a good thing -- it is a more accurate understanding of the potential error in radiocarbon dates.

But what can we conclude about the time interval represented by early modern humans (or more properly, of early Aurignacian sites, since it is far from demonstrated that they were left by modern humans) and their dispersal across Europe?

Looking at the Mellars graph, his interpretation is apparent from his numbers. The leftmost European site on his graph is number 4, Bacho Kiro. It is estimated at more than 43,000 radiocarbon years; Mellars put it at more than 46,000 "calibrated" years. The youngest site (17, Roc de Combe) is 35,000 radiocarbon years; Mellars put it at 40,000 "calibrated" years. So the interval from oldest to youngest is 11,000 radiocarbon years, compared to only 6,000 "calibrated" years, according to Mellars:

[W]e can now see from the new calibrated chronology that this must be shortened to at most about 6,000 yr (at least in the more central and northern parts of Europe), with periods of overlap within the individual regions of Europe (such as western France) of perhaps only 1,000-2,000 yr. Evidently the native Neanderthal populations of Europe succumbed much more rapidly to competition from the expanding biologically and behaviourally modern populations than previous estimates have generally assumed.

But again, this is quite plainly wrong. First, it assumes the reduction in length of the error bars, which the calibration process shows must actually be greatly increased in length. And second, it ignores the visually apparent "kink" in the calibration curve over just the time range represented by the early Aurignacian. That "kink" means that true dates over a very wide time range will come out with the same radiocarbon date estimate.

And remember that Neandertals persisted well after 40,000 years in the sequence, with a number of dates after 33,000 years ago now (and possibly as recent as 28,000). These dates are radiocarbon years, and calibrated dates might be older (and closer to the early Aurignacian "calibrated" dates). But they don't fit into the blitzkrieg model very readily.

The real question is whether the radiocarbon data address the pattern of change in biology and archaeology -- a sudden shift might still be a piecewise or mosaic transition, and a long shift might nevertheless have discrete boundaries. I think there is sufficient evidence that the transition in Europe was mosaic in character. From there, the pace of change (and migration or gene flow) might be 6000 years or 20,000, it doesn't much matter from the perspective of pattern. On the other hand, folks interested in climatic forcing and other more time-centric scenarios might care very deeply about whether we are looking at a short or long timeframe.

In any event, it is safe to conclude that the evidence for a rapid dispersal based on these data is pretty much all based on faulty statistics.

By the way -- has anybody else noticed that the vast preponderance of totally wrong research lately has been in Nature?

References:

Mellars P. 2006. A new radiocarbon revolution and the dispersal of modern humans in Eurasia. Nature 439:931-935. DOI link

Turney CSM, Roberts RG, Jacobs Z. 2006. Archaeology: Progress and pitfalls in radiocarbon dating. Nature 443:E3. DOI link

Very nearly this time last year, I commented on a paper by Brad Gravina, Paul Mellars, and Christopher Bronk Ramsey concerning the stratigraphy of the Châtelperron type site. The paper documented evidence for an "interstratification" of the Châtelperronian and Aurignacian-type industries in the site stratigraphy. If these industries were interstratified, it provides evidence for the early appearance of Aurignacian peoples, and their possible influence on Neandertals who apparently manufactured the Châtelperronian.

Later, Mellars discussed the result in a commentary about the importance of new radiocarbon stratigraphies. Along with new radiocarbon dates from other sites, the Châtelperron evidence seemed to make clear the importance of new technologies and old-fashioned detective work in setting straight the course of events during the Upper Paleolithic in Europe.

Well, now a new paper by João Zilhão and colleagues has set out the reasons why the Châtelperron work was all wrong. It basically comes down to jumbled stratigraphy:

The Grotte de Fées at Châtelperron originally contained important Châtelperronian and Mousterian deposits. Both were palimpsests of remains left in the framework of repeated, short-term, nonresidential human occupations alternating with carnivore denning; scant Aurignacian and Solutrean objects testify to later, sporadic human visits. The presence in levels B4-5a of low percentages of edge-damaged and surface-weathered lithic objects indicates some syndepositional disturbance, perhaps in relation to flooding by the stream running 6 - 8 m below.

After its discovery, this very small site was intensively exploited with little concern for the stratigraphy, resulting in the accumulation of successive generations of disturbed deposits. Consideration of the totality of the evidence shows that, as at El Pendo, Le Piage, and Roc-de-Combe, the pattern of Aurignacian -- Châtelperronian interstratification only can be an artifact of postdepositional disturbance, whether that disturbance was caused by natural processes in the Pleistocene or by archeological excavation and fossil hunting in the 19th century (Zilhão et al. 2006:12648).

Should we believe it? Well, there is that small detail about the stream -- seems like the sort of thing that you shouldn't leave out if you are trying to establish whether 10 or so Aurignacian-type tools are part of a continuous sequence or not. There is also a fairly good picture of the stratigraphic profile, which certainly looks like a jumble in the crucial parts.

The paper also documents artifactual and faunal evidence for a jumbled stratigraphy -- most notably showing strong biases in artifact size and surface weathering among the crucial layers. They find that artifacts in the upper "B" levels of the site (B1-3) were likely left very sporadically when the cave was mainly occupied by carnivores, giving strong possibility for the intrusion of later material into the next lower layer, B4. The fact that a Solutrian-type artifact was found in these upper B levels would seem to confirm the long period over which they were accumulating artifacts.

So yes, I believe it -- it is a really good case study in why archaeologists have so much trouble with sites of this time period. And in this instance, all the signs point to the real possibility of stratigraphic confusion.

The paper critically discusses other evidence for pre-Châtelperronian Aurignacian in Western Europe:

The case for a precocious Aurignacian further rests on interstratifications with the Châtelperronian at El Pendo (Spain), Roc-de-Combe, Le Piage, and Grotte des Fées at Châtelperron (France), all of which are questionable. At El Pendo, the different levels of the sequence, a slope deposit at the base of a large uvala, feature a diverse mix of archeological materials (an Upper Paleolithic sagaie, for instance, was found 5 m below the purported interstratification, the overlying deposits containing hundreds of Mousterian-like flakes and cores). At Le Piage, a Châtelperronian lens interstratified in the Aurignacian was described for a small area that, in fact, corresponds to a slope deposit yielding a mix of Châtelperronian, Aurignacian, and surface-weathered Mousterian items throughout the entire sequence. At Roc-de-Combe, an Aurignacian lens interstratified in the Châtelperronian reportedly ex isted under the cave's overhang (the external area featured a single, Mousterian level, and the internal area featured a normal Aurignacian-over-Châtelperronian sequence), but this "level" was a post facto theoretical construct assembled from several true excavation units, all of which featured a mix of Gravettian, Aurignacian, Châtelperronian, and Mousterian pieces (Zilhão et al. 2006:12643, citations elided).

The lack of any good evidence for such interstratification at any other site is why the Grotte des Fées was assigned such importance by Gravina et al. (2005) and Mellars (2006), but it is illuminating to see this terse review. Zilhão and colleagues conclude that the most credible explanation for the total pattern of evidence is that the Châtelperronian preceded the Aurignacian in Western Europe. The paper takes this as support for an autochthonous origin of the Upper Paleolithic Châtelperronian in Western Europe, and for relative cognitive sophistication among the Neandertals.

References:

Gravina B, Mellars P, Ramsey CB. 2005. Radiocarbon dating of interstratified Neanderthal and early modern human occupations at the Chatelperronian type-site. Nature 438:51-56. DOI link

Mellars P. 2006. A new radiocarbon revolution and the dispersal of modern humans in Eurasia. Nature 439:931-935. Full text (subscription)

Zilhão J, d'Errico F, Bordes J-G, Lenoble A, Texier J-P, Rigaud J-P. 2006. Analysis of Aurignacian interstratification at the Châtelperronian-type site and implications for the behavioral modernity of Neandertals. Proc Nat Acad Sci USA 103:12643-12648. DOI link

Thank goodness for blogs. Thanks to GNXP and Dienekes, I've been looking at the new paper by Paul Mellars. Here's the title:

Why did modern human populations disperse from Africa ca. 60,000 years ago? A new model

The thing is, this is nearly indistinguishable from Richard Klein's model. There are only two possible distinctions between Mellars and Klein. The first is with regard to the Skhul and Qafzeh hominids: Klein interprets these as "near-modern" samples lacking significant evidence of modern behavior; Mellars accepts evidence for symbolic behavior at Qafzeh including possible grave goods, perforated shells, and pigment use.

The second is that Mellars interprets Klein as supporting a "sudden change in the cognitive capacities of the population involved, entailing some form of neurological mutation" (Mellars 2006:9384) at 40,000 to 50,000 years ago. In contrast, Mellars supports either a sudden change or a gradual change in cognitive capacities, entailing either neurological mutations or environmental changes, at 80,000 years ago.

So I guess the only difference is the timing, since I read Klein as essentially agnostic about the mechanism of cognitive evolution (he mentions mutation as a possible mechanism, but clearly has no specifics on this point).

And if Mellars is willing to accept that the Qafzeh burials are evidence of symbolic behavior, it is hard for me to see how his position can be differentiated from d'Errico, who after all has only pointed out that similar evidence for Neandertal symbolic behavior must be interpreted in similar cognitive terms. Now that seems to me like an impossible coincidence...

Brumm and Moore (2005) review the "symbolic revolution" in the light of the Australian archaeological record.

In brief, until the mid-Holocene, there is no strong evidence in the Australian record for the systematic use of symbolism. What evidence there is consists of isolated and sporadic examples. In contrast, the mid- to late-Holocene exhibits a pattern of changes like that in Upper Paleolithic Europe, at least with respect to symbolic behavior:

As decades of archaeological research have revealed, Aboriginal social and economic systems appear to have 'intensified' and become more complex in the last 7000 years, but particularly during the middle to late Holocene (Allen and O'Connell 1995; Beaton 1985; Lourandos 1983; 1997; Lourandos and Ross 1994). Fishing technologies like rock walls, weirs, shell hooks and other equipment, as well as complex technologies for processing toxic plants appear towards the late Holocene, suggesting increased diet breadth and an intensification of marine and plant food resource extraction (Evans and Jones 1997). Along with and possibly closely related to economic intensification there appears to have been a marked increase in site usage and population density, synchronous with a growth in the size and frequency of social aggregation (Lourandos 1997). Long-distance exchange networks circulating such articles as stone artefacts, ochre and pearl shell throughout the Australian continent (see McBryde 1987) date to the middle to late Holocene, with the most extensive trading networks emerging only within the last millennium or so (Davidson et al. in press; Hiscock 1988; Tibbett 2002). Stone technology increases in complexity, a process which includes the emergence of Levallois-like stone-reduction methods around 6000 years ago (Dortch 1977; Dortch and Bordes 1977; Moore 2003a). Blade-based lithic industries and backed artefacts become well established at about the same time (Figs. 4 and 5). Ground-edge axes become widespread in the middle Holocene after a Late Pleistocene hiatus (Morwood and Hobbs 1995), and distinctive tools like large bifaces (Moore 2003b), bifacially-flaked points (Akerman and Bindon 1995), and tula adzes (Moore 2004) emerge in the Holocene (Brumm and Moore 2005:165-166).

The passage goes on to discuss changes in artistic representation, religious systems, and burial practices that also occurred in the mid-Holocene. This would seem to be the closest thing in Australia to a "revolution", but on temporal and climatic grounds, it probably is an Australian manifestation of the expansion of human population size that also occurred in pre-agricultural populations in the Old and New World alike.

The paper contrasts a "short-range" model for the evolution of behavioral modernity with a "long-range" model. In the "short-range" model, the behavioral "package" of modern humans evolved recently and quickly resulted in the dispersal of a single population across the Old World. Australians in this hypothesis must descend from this initial dispersing population, which was intensively symbol-making. Brumm and Moore consider this view problematic, since symbol-making was evidently not a central focus of Australian behavior until the Holocene:

On the other hand, if one accepts that the first colonizers were behaviourally modern -- and this is the opinion of most Australian researchers -- then the criteria used by the 'short-range' camp to identify
modern human behaviour in the Old World is undermined. The Australian record demonstrates that fully modern symbolling humans did not necessarily produce a repetitive package of symbolic traces. This in turn supports Wadley's (2001) position that a single case of symbolic storage may be sufficient for identifying modern human behaviour. The 32,000-year-old Mandu Mandu shell beads are perhaps the least ambiguous evidence for symbolic storage recovered to date from the Australian Pleistocene; they can, by themselves, confirm Davidson and Noble's (1992) contention that the first colonizers of Australia were behaviourally modern.

A pause, for dramatic effect...

Furthermore, if modern symbolic behaviour in early Australia produced a patchy archaeological record, there is no clear reason for rejecting the 'modernity' of the Middle Pleistocene record of the Old World solely on the basis of its patchy distribution.

We suggest that the Holocene Australian example could indicate that the rapid pace of change during the symbolic revolution in Africa and Europe roughly 50,000-40,000 years ago has little to do with the emergence of modern human behaviour and more to do with social, demographic, or other causes. It is possible, for example, that these changes simply reflect the reaching of an organizational threshold, that regional populations had reached a level at which new channels of information transmission became necessary to alleviate conflict and establish boundaries (Kuhn and Stiner 1998, 157) (Brumm and Moore 2005:167-168).

This also characterizes the views of Barton et al. (1994, discussed in this post) regarding the intensification of symbolic expression, and particularly art, in Upper Paleolithic Europe. There also, the real intensification of symbolic expression may not have corresponded with the arrival of modern humans, but instead apparently with demographic change and greater population densities.

References:

Brumm A, Moore MW. 2005. Symbolic revolutions and the Australian archaeological record. Camb Arch J 15:157-175. DOI link

That's "Upper Paleolithic", not "Upper Peninsula." Barton et al. (1994) discuss the interpretation of Paleolithic art in Western Europe. A good short summary is this passage (p. 190):

Viewing art as a communication medium that monitors information flow allows us to propose an explanation for observed patterns in Palaeolithic and post-Palaeolithic art, and to model changing alliance networks in European forager populations from the late Pleistocene through the early Holocene.

They conclude that the tradition of parietal art in Southwest France and northern Spain reflects demographic pressures associated with increases in population density, stress on existing alliance networks, and claims for property rights.

The information exchange approach taken here argues that parietal art is an example of Wiessner's emblemic style; that emblemic style is, among other things, a monitor of demographic stress, and that the appearance of parietal art in late Pleistocene Europe resulted from the closing of social networks under increasing population density (ibid:199).

They suggest that this use of emblemic style is merely an archaeologically visible instance of a system based in archaeologically invisible referents, and that this visibility is a function of group size and resource availability:

As noted, both assertive and emblemic style almost certainly existed among prehistoric foragers, but are not usually recoverable archaeologically. Ethnographic data indicate that emblemic style in forager contexts is often associated with features of the landscale (e.g. Denbow 1984; Lewis-Williams 1984). That is, it functions to identify sacred localities, prominent topographic features, the boundaries of more or less exclusive economic territories and other geographic landmarks. Under conditions of low population density, changing group membership and open social networks, the significance of such landscape features is transmitted from one generation to the next by means of the oral traditions of small, fluid social units; the physical marking of such features is rarely necessary. With aggregation, however, the need for more effective means of both inter- and intra-group communication arises. It becomes necessary to reinforce oral tradition within larger social units, whose members might not participate in a single tradition nor interact with one another on a regular basis.

I wanted to note the contrast they draw between two "explanatory paradigms" for patterns in Paleolithic art:

Art and social interaction

The first sees distributional patterning in Paleolithic art, and more generally style, as a monitor of the degree of cultural affinity among social groups through time or in terms of shared cultural traditions. This 'social interaction' model has roots in both the Old and New Worlds. In North America, it dates back to A. L. Kroeber, Clark Wissler and the 'culture area' studies of the 1930s. Social interaction theory defined style in a strongly normative way as repetitive behavior that acts as a kind of psychological 'filter' to constrain variety and reduce information overload. Style functions at the level of the individual and is essentially passive; that is, it reflects normative constraints learned unconsciously through enculturation. In art and in artefact design, style is construed to exhibit modal properties taken to reflect, an a more or less direct way, group norms and values. These modal properties are often considered to be isomorphic with the temporal and spatial boundaries of identity-conscious social units -- in other words, an ideational definition of style, but with alleged material correlates (Clark 1993) (ibid.:186).

In other words, "style" in artifacts reflects the boundaries of meaning in the minds of people who made the artifacts. It is unintentional -- a byproduct of the process of learning a limited set of information. Because of a lack of intentionality, the analysis of style may uncover the social units themselves, consisting of individuals who shared boundaries of meaning. Style is therefore a marker of cultural affinity.

Art and information exchange

The second approach to art is essentially a functionalist one that views it as the remains of communication systems involving the exchange of information (Braun and Plog 1982). As employed here, the 'information exchange' theory of style originated with Polly Wiessner (1983, 1984, 1985), who views art as an act of social communication defined, at various levels and scales, by style. Style, in turn, as its behavioral basis in a fundamental human cognitive process: the personal and social identification of images through visual comparison. In sharp contrast to the pattern searches of social interaction theory, style is defined here by its determining processes, rather than by its material conditions.

In this paradigm, "style" is a functional element of artifacts that may or may not correspond to cultural entities. It has an adaptive function in the intentional transfer of information, such as information about social status or property. Since the imposition of style is deliberate, it does not mark cultural units in a straightforward way, but instead marks patterns of activity that may or may not be linked to cultural entities.

I like this second concept, because it assumes that people are intentional agents with respect to stylistic representation. But I think that elements of the first are also necessary, since there clearly are boundaries to meaning that are important in the function and interpretation of stylistic information. Indeed, without boundaries to delimit meaningful representations, there can be no transfer of information (The importance of these delimitations on meaning is well illustrated by modern art, which is often more about the placement of boundaries to meanings than it is about stylistic or representational elements).

References:

Barton CM, Clark GA, Cohen AE. 1994. Art as information: explaining Upper Palaeolithic art in Western Europe. World Archaeol. 26:185-207.

A paper (PDF) by Tom Higham and colleagues presents a redated chronology for the late Neandertals from Vindija, Croatia. There are two directly dated hominid specimens (Vi-207 mandibular fragment and Vi-208 parietal fragment). Earlier work by Smith et al. (1999) had dated the two specimens to between 28,000 and 29,000 BP.

The current paper notes a possible problem with contamination by more recent carbon in the specimens, which would make the dates younger than they ought to be. So Higham et al. (2006) used a new method that filters out small molecules from the collagen extracted from the bone. This resulted in older date estimates, 32,400 +- 800 BP, and 32,400 +- 1800 BP, respectively.

There is a news release describing the work.

The paper also provides a useful short review of the current radiocarbon chronology of late Neandertal and early modern skeletal remains in Europe. This quote is illuminating:

This situation currently makes it difficult to use an archaeological complex, such as the Aurignacian, as a correlate for the spread of modern humans across Europe during this biocultural evolutionary transitional time period (in contrast to Mellars 2005). Several factors play into this ambiguity. It is possible that the dating difficulties described above with reference to Vindija may be more widespread than hitherto anticipated, and that the 4,000-year gap between the earliest directly dated modern humans and the earliest Aurignacian is a function of radiocarbon acccuracy on the few dated specimens...

I pause the quote to point out that the authors earlier note the lack of association with skeletal remains for the early Aurignacian; thus the question is whether the early Aurignacian itself is dated too early. Of course, if the problems with the radiocarbon chronology were of the same type that they found with the Vindija bones (i.e., contamination with young carbon), the other dates wouldn't be too old, they would be too young. So it would have to be some other problem. Maybe all the supposedly old early Aurignacian will turn out to be

The gap may be a function fo the scarcity of Aurignacian human remains and the low number of dated specimens...

Although perhaps one wouldn't expect that all the dated specimens would be archaeologically recent compared to the Aurignacian as a whole...

Alternatively, it may be a result of semiindependence of the spread of the Aurignacian (a cultural process) and the westward dispersal of early modern humans (a biological population process) (Higham et al. 2006:555).

The fact is that we don't currently know. It seems sort of unlikely that the current collection of fossils and sites is adequate to tell us -- if there were skeletal associations with several early Aurignacian sites, that would be one thing, but there just aren't. The current chronology does place Mladec younger than Vindija, so the prior overlap of Neandertal and early modern specimens in central Europe is no longer. It makes it even more suggestive that the Vindija G1 assemblage includes Aurignacian elements.

References:

Higham T, Ramsey CB, Karavanic I, Smith FH, Trinkaus E. 2006. Revised direct radiocarbon dating of the Vindija G₁ Upper Paleolithic Neandertals. Proc Nat Acad Sci USA 103:553-557. Abstract

Smith FH, Trinkaus E, Pettitt PB, Karavanic I, Paunovic M. 1999. Direct radiocarbon dates for Vindija G1 and Velika Pecina Late Pleistocene hominid remains. Proc Nat Acad Sci USA 12281-12286. Full text online

This LiveScience story covers a paper by David Steadman that seems not to be available yet at PNAS.

The arrival of humans onto the American continent and the great thaw that occurred near the end of the last Ice Age both occurred at roughly the same time, about 11,000 years ago. Until now, scientists were unable to tease apart the two events.

To get around this problem, David Steadman, a researcher at the University of Florida, used radiocarbon to date fossils from the islands of Cuba and Hispaniola, where humans didn't set foot until more than 6,000 years after their arrival on the American continent.

The West Indian ground sloth, a mammal that was the size of a modern elephant, also disappeared from the islands around this time.

"If climate were the major factor driving the extinction of ground sloths, you would expect the extinctions to occur at about the same time on both the islands and the continent since climate change is a global event," Steadman said.

Seems simple.

Why is it that the BBC always picks up stories like this one? (via palanthsci)

The 20cm-long, 3cm-wide stone object, which is dated to be about 28,000 years old, was buried in the famous Hohle Fels Cave near Ulm in the Swabian Jura.

The prehistoric "tool" was reassembled from 14 fragments of siltstone.

Its life size suggests it may well have been used as a sex aid by its Ice Age makers, scientists report.

Did you have to go there, BBC? "Tool"?

Go to the story. See the picture. Cringe at quotes like this one from Nick Conard:

"In addition to being a symbolic representation of male genitalia, it was also at times used for knapping flints"

And please try to consider what it says about Neandertals that they never made one.

It's not "The Rabbit", but I suppose they had to make do...

A few weeks ago, I posted on recent work by Clive Trueman et al. (2005) that showed a prolonged coexistence of some extinct Australian megafauna with early humans.

Today, I saw this new paper by Gifford Miller and colleagues. Here's the abstract:

Most of Australia's largest mammals became extinct 50,000 to 45,000 years ago, shortly after humans colonized the continent. Without exceptional climate change at that time, a human cause is inferred, but a mechanism remains elusive. A 140,000-year record of dietary delta13C documents a permanent reduction in food sources available to the Australian emu, beginning about the time of human colonization; a change replicated at three widely separated sites and in the marsupial wombat. We speculate that human firing of landscapes rapidly converted a drought-adapted mosaic of trees, shrubs, and nutritious grasslands to the modern fire-adapted desert scrub. Animals that could adapt survived; those that could not, became extinct.

The paper has an accompanying commentary by Christopher Johnson that explains it well:

Miller et al. studied past diets of the emu (Dromaius novaehollandiae) and an even larger flightless herbivorous bird, the extinct Genyornis newtoni (see the first figure), in the arid and semi-arid regions of the south Australian interior. By analyzing carbon isotopes in individually dated eggshells, they were able to compare the contributions of plants that use the C4 photosynthetic pathway (mainly tropical and arid-adapted grasses) and those that use the C3 pathway (most shrubs, trees, and nongrass herbs) to the diet of the birds that laid the eggs. Their collection of eggshells covers the past 140,000 years, encompassing the whole of the last glacial cycle.

Miller et al. found a sudden change in emu diet between 50,000 and 45,000 years ago. Before 50,000 years ago, emus had variable diets, with a strong contribution from C4 plants; after 45,000 years ago, they ate mostly C3 plants. Genyornis eggshells were common before 50,000 years ago, but they abruptly disappeared at the same time as the diet of the emu changed. Before then, Genyornis also ate a mixture of C3 and C4 plants, but its diet was much less variable than that of the emu through the same period, which suggests that it was a more specialized feeder (Johnson 2005:255).

This paper argues that climate change could not be responsible because there was no climate change 45,0000 years ago. Trueman et al. (2005) argued that climate change was likely responsible because the animals survived alongside humans until 30,000 years ago, when climate changes did happen. Neither the paper nor the commentary note or cite Trueman and colleagues' work. This is not necessarily a surprise, since the papers were in press at the same time, but seems like an omission.

An article by Nature news does notice the contradiction, and has this to say:

Fossils found at Cuddie Springs, New South Wales, seem to indicate that ancient fauna lived side-by-side with humans for several thousand years before finally succumbing to encroaching desertification as little as 30,000 years ago (see "Did climate shift kill off giant Australian animals?").

But Miller argues that more accurately dated fossils are needed to support this theory. "The Cuddie Springs dating remains very contentious," he says. "Most agree that the extinction event occurred between 50,000 and 45,000 years ago."

Well it is always true that better dates would help. But I think we have a lot to learn about the dynamics of ancient mass extinctions, also. Burning could well have changed the Australian habitat in ways congenial to some animals (that is, after all, why people started burning to begin with) but ultimately bad for others. But could it have wiped out the entire ecological niche of a species? Or was a reduced population ultimately rendered more susceptible to human predation? Or climate change? Or were they simply outcompeted by other animals who could handle the loss of C4 [corrected on 8/1/05] resources? Lots of questions, few answers.

References:

Johnson CN. 2005. The remaking of Australia's ecology. Science 309:255-256. Full text online

Miller GH. et al. 2005. Ecosystem collapse in Pleistocene Australia and a human role in megafaunal extinction. Science 309:287-290. Full text online

Australia is well known for its unique animals. It has the most extensive diversity of marsupial mammals found anywhere in the world. Together with nearby New Guinea, it is home to the only monotreme mammals in the world, the platypus and echidna. It has not one but two species of very large flightless birds, the emu and cassowary. And until historic times, its only placental mammals were humans, dingos, and bats. So much is common knowledge.

But before the arrival of humans, the Australian fauna was even more extensive for the inclusion of many kinds of very large animals, or megafauna. These include Diprotodon, which is often compared to a rhinoceros in size and adaptive pattern, Zygomaturus, which was a somewhat smaller, bison-sized herbivore, the "marsupial lion" Thalacoleo carnifex, the giant 9-foot kangaroo Procoptodon goliah, and the large flightless bird Genyornis. A guide to the extinct Australian megafauna is available from the Museum Victoria site.

What happened to these large animals? Some archaeologists have hypothesized that the appearance of humans in Australia by 50,000 years ago may have led directly to the extinction of the megafauna. This hypothesis would be essentially like that proposed for the disappearance of the American megafauna, including mammoths, giant ground sloths, horses, and many other species in the terminal Pleistocene, called the "overkill" hypothesis. A new paper in PNAS by Clive Trueman and colleagues (2005) addresses this hypothesis by examining the archaeological evidence for megafaunal extinction.

In Australia, the evidence for the "overkill" hypothesis has mainly been derived from the coincidence of the arrival of humans and the extinction of the megafauna. As described by Trueman et al. (2005), most studies have placed the most recent evidence of megafaunal elements at around 46,500 years ago. The present evidence for human occupation of Australia places it certainly by 45,000 years ago, possibly as early as 60,000 years ago. Some archaeologists have persistently suspected that the date of occupation may be even earlier, and occasionally dates for archaeological sites have emerged to support an earlier date, only later to be questioned and retracted. In any event, there has been relatively little evidence for a substantial period of interaction of humans and megafaunal species, as would be documented by finding these species together with archaeological remains for a substantial period of time.

The current study examines one such site. From the abstract:

A number of key sites with megafauna remains that significantly postdate 46.5 ka have been excluded from consideration because of questions regarding their stratigraphic integrity. Of these sites, Cuddie Springs is the only locality in Australia where megafauna and cultural remains are found together in sequential stratigraphic horizons, dated from 36-30 ka. Verifying the stratigraphic associations found here would effectively refute the rapid-overkill model and necessitate reconsideration of the regional impacts of global climatic change on megafauna and humans in the lead up to the last glacial maximum. Here, we present geochemical evidence that demonstrates the coexistence of humans and now-extinct megafaunal species on the Australian continent for a minimum of 15 ka (Trueman et al. 2005:8381).

The chemical analysis in the paper was concentrated upon demonstrating that the bone remains actually belonged within the sediments where they were found, so that the site stratigraphy is a true record of the intercalation of human artifacts and megafaunal remains. A 1996 report at the University of Sydney Archaeology department documents the Cuddie Springs site in some detail, including the evidence for butchering of megafaunal species. So the find is not new, but its improved documentation has some substantial importance in the context of megafaunal extinction in Australia.

Here is an excerpt from the discussion:

The verification of late survival for at least some Australian megafauna has broad ramifications. Although prolonged persistence of the megafauna after human arrival certainly does not rule out a role for humans in their extinction, it does demonstrate that the extinction of the megafauna occurred over a time scale of many thousands of years. In Australia, there is no evidence for either megafaunal kill sites or contemporaneous technologies typically associated with big-game hunting (such as spear-throwers or stone-tipped projectile points). Arguments for human-mediated megafaunal extinction have commonly rested on the strength of a circumstantial case (i.e., that extinctions preceded significant climate change); therefore, humans must have been responsible. However, sites other than Cuddie Springs have yielded megafauna remains that are significantly younger than 46.5 ka, and an increasing body of evidence attests to the onset of climatic instability in Australia from ~50 ka, culminating in full glacial conditions as early as 30 ka. Climate instability is characteristic of the Late Pleistocene and is coincident with faunal extinctions on all continents (Trueman et al. 2005:8383-8384, citations elided).

In other words, climate change is very much in the game for explaining these extinctions. On the other hand, there is no real way to take humans out of the game. People were clearly hunting these animals as they expanded in population size at an unknown rate. In other regions of the world, increases in human population size were associated with increases in the breadth of prey species and apparent impacts on low-recovery rate species. Whether Australia is another example of this phenomenon will require not only a better understanding of the timing of megafaunal extinctions, but also a better modeling of ancient human population dynamics.

References:

Trueman CNG, Field JH, Dortch J, Charles B, and Wroe S. 2005. Prolonged coexistence of humans and megafauna in Pleistocene Australia. Proc Nat Acad Sci USA 102:8381-8385. PNAS online