Middle Paleolithic

Well, I already snarked on the science headlines that have been claiming volcanoes "wiped out" the Neandertals. Some variation of this story, swapping in a different Neanderkiller, has been circulating since around 1890. But is there any truth to the headlines?

(see UPDATE below)

The source of the story is a paper in the October issue of Current Anthropology, by Golovanova and colleagues [1]. The paper reviews the chronology of Mezmaiskaya Cave, a site occupied by Neandertals and successive Upper Paleolithic peoples, in the Russian Caucasus. This site produced the skeleton of an infant, from which DNA evidence has been recovered. As Golovanova and colleagues describe, the deposit additionally contains volcanic ash from two eruptions that happened around 40,000 years ago.

The latter of the two eruptions appears to coincide with a long abandonment of the site:

Hominin occupation of Mezmaiskaya Cave changed dramatically after the later volcanic eruption represented in layer 1D. This eruption was probably more powerful than that in layer 2B-1. Layer 1D has a thickness up to 0.7 m and in some areas is composed of a relatively clean sediment lacking any inclusions (fig. A10). Limestone fragments, bones, and lithic artifacts are absent, and even pollen grains are rare. Pollen data show that extreme deterioration to a very cold and dry climate occurred in this time period....A chemical analysis of layer 1D indicates that the volcanic ash apparently derives from an eruption in the Kazbek volcanic province that occurred around 40,000 years ago. Because no Neanderthal specimens or MP lithic industries postdate layer 1D at Mezmaiskaya, this eruption seems to have significantly disrupted the ecological niche of local Neanderthals, possibly resulting in their rapid disappearance in this region.

The Kasbek volcanic province is in the Caucasus, so we're talking about a large eruption relatively local to the site. This is the sort of event you might well expect to have a strong impact on a dispersed hunter-gatherer population. The Middle Paleolithic people (presumably Neandertals) might have locally declined in numbers, or they might have moved on. The region need not have been abandoned entirely; a new population might have entered the area without using the same site. In this case, when new people began to use the site much later, the newbies were using an Upper Paleolithic industry.

A relatively local effect of volcanism in the Caucasus is one thing, but the extinction of Neandertals across western Eurasia is quite a bit more. How does the paper go from local event to a regional extinction?

The local eruption was the second event to leave ash in the Mezmaiskaya sequence. The first was a different eruption from Mt. Elbrus, which had a smaller impact than the second, as discussed below.

At issue in the paper is the possible coincidence of the second eruption and consequent abandonment of the site with a much larger volcanic event in Italy:

The CI [Campanian Ignimbrite] eruption from the Phlegrean Fields, southern Italy—the largest eruption documented in the Mediterranean region during the past 200,000 years (Wohletz, Civetta, and Orsi 1999)—drastically impacted European ecosystems. The most recent numerical (⁴⁰Ar/³⁹Ar) age determinations for CI eruption vary from to BP and cluster around 40,000 BP (Fedele, Giaccio, and Hajdas 2008:839).

This eruption produced the CI in Italy and Y5 tephra in Central and Eastern Europe and Eastern Mediterranean (Fedele et al. 2003; Fedele, Giaccio, and Hajdas 2008). High-altitude clouds of volcanic ash from this eruption had a significant effect on global climate. The resulting ash fall covered km2 of land and sea (fig. 1), and the Y5 tephra layer accumulated in the Eastern Mediterranean as far as Cyprus—more than 1,500 km from its source (Mussi 2001:191). The Y5 tephra is also identified in the EUP sequence at Kostenki in the Middle Don River in Russia (Holliday et al. 2007). In Eastern Europe, the ash layer varies from 1–2 cm in the eastern limit (between Penza and Rostov) to 5–8 cm in the west and southwest (southern Ukraine and Moldova) and averages about 3–4 cm (Laverov et al. 2005:51). Obviously, the area affected by this ash fall was much larger than the documented Y5 tephra sites.

Golovanova and colleagues propose the hypothesis that the climate effects of this CI event caused the demise of the Neandertals:

Our new data provide support for the hypothesis that the MUP transition in western Eurasia coincides with one of the most globally significant volcanogenic catastrophic events in the recent history of the earth. The large and coeval volcanic eruptions (from an unusually large CI eruption in the Apennines to a smaller eruption in the Caucasus) had a sudden and devastating effect on the ecology and forced the fast and extreme climate deterioration (so-called volcanic winter, perhaps comparable to the effect of nuclear winter) of the Northern Hemisphere in the beginning of Heinrich Event 4. We guess that this catastrophe likely may have both drastically destroyed the ecological niches of Neanderthals, possibly resulting in the mass death of hominins and prey animals and the severe alteration of foraging zones, and caused Neanderthal depopulation from Central Europe to the Caucasus.

That's a very clearly stated hypothesis. A volcanic eruption initiated climate effects that the regional population of Neandertals could not survive.

However, Golovanova and colleagues include in their paper several critical facts that run against this hypothesis:

1. The Mezmaiskaya sequence itself shows Middle Paleolithic people returning and proliferating after a large relatively local eruption. The Elbrus eruption apparently left ash in layer 2B-1, with a low density of bones and a very low frequency of bison compared to caprids. The excavators interpret the layer as a very low-intensity use of the cave. The pollen evidence suggests a "cold, dry climate". In other words, the paleoclimate and faunal evidence are both consistent with the hypothesis that the eruption had effects on Neandertal populations in the Caucasus. But then the Neandertals apparently returned in force:

The intensity of site use increased, however, during the accumulation of the upper MP layers 2A and 2 when the climate become cool and wet. Although the lithic industry changed slightly after the environmental crisis of layer 2B-1, it still remained typically MP Eastern Micoquian. Skeletal and mtDNA evidence indicates that Neanderthals produced both the earlier and the later MP industries at Mezmaiskaya (Briggs et al. 2009; Golovanova et al. 1999; Green et al. 2010; Ponce de Leon et al. 2008). Thus, the late MP environmental crisis at the cave had repercussions for local Neanderthals but did not cause a break in the continuity of occupation or technology.

That makes it seem pretty unequivocal. Neandertals survived and effectively adapted to at least one volcanic event in this area. That eruption did not kill them off, and it did not leave the area devoid of Neandertals in a way that facilitated a "modern human invasion."

It was only after the second volcanic event that Middle Paleolithic people declined at the site.

At issue is whether this second event was coincident with the CI eruption. The ash in the Mezmaiskaya sequence is not from the Y5 tephra, it is attributable to a much nearer source. I do not fully understand why the authors attribute this second event to the same time as the CI event; the time between layers 2 (terminal Mousterian) and 1C (early Upper Paleolithic) appears to have occupied a few hundred years, between 32,000 and 34,000 radiocarbon years BP. Calibration will move those dates older by a few thousand years (I discussed radiocarbon calibration a few years ago). But I think the CI eruption, around 40,000 years ago, doesn't fit well with this later event. It might fit with the earlier eruption, in my view, as Elbrus lava flows include 40,000 BP.

In any event, I think the associations of either local volcanic event with the larger CI event is at best uncertain. The record at the site makes it pretty clear that Neandertals were effectively adapting to the changing local climates and faunal abundance that coincided with the first eruption.

2. The initial Upper Paleolithic of Kostenki had appeared before the Y5 tephra was deposited. I wrote about the identification of this Y5 tephra at Kostenki a couple of years ago ("An earlier initial Upper Paleolithic at Kostenki"). As my post indicated, the identification of the ash layer with the Campanian Ignimbrite event suggested an earlier date for the initial Upper Paleolithic on the Russian Plain.

From the standpoint of the Neandertal volcanic winter hypothesis, this sequence of events is a problem, which Golovanova and colleagues discuss:

In any case, with or without the Kostenki addition, the few CI-bearing sites show that this eruption could have also extinguished the first wave (Proto-Aurignacian) of EMH expansion into Europe (Fedele, Giaccio, and Hajdas 2008): “At all key sites, where sedimentary resolution is good, the CI tephra directly seals archaeological layers that contain assemblages of the MUP mosaic, often variants of ‘Aurignacian’-like or so-called Early Upper Paleolithic Industries. … The layers above the CI tephra, where they are not culturally sterile, contain later and often much later properly defined Upper Paleolithic industries” (841). Thus, the CI-bearing sites demonstrate clear evidence of the break in habitation and culture change—a whole gamut of archaeological attributes for population replacement.

The volcano is supposed to explain the MUP transition, but occurs earlier than the MUP transition in some areas, but later in others. Golovanova and colleagues propose an ad hoc hypothesis to account for this mismatch: some early Upper Paleolithic modern humans were also wiped out.

Many researchers might find this idea tempting. It might, for example, explain why the (few) skeletal remains of the earliest Aurignacian people have such a high proportion of Neandertal features. We could propose that the initial Upper Paleolithic represents a degree of population mixture that later populations do not; the discontinuity between them could have been caused by climate extremes.

But we don't need climate or volcanism. Later Upper Paleolithic people retained similarities to Neandertals, which reduced in frequency over time. This is most readily explained by continued gene flow into a sparse European population from West Asia. A volcano-induced climate catastrophe is superfluous: It doesn't add to the explanation of a sustained genetic transformation of Europe that continued through the later Upper Paleolithic and Neolithic.

3. "Catastrophes" are not rare. The record of climate change during the last glaciation shows frequent strong oscillations. Some of these occurred at the same time as known eruptions, and so might be associated with them, but most climate oscillations have no obvious cause. Up to 40,000 years ago or so, the Neandertals survived them all. They survived the Toba event, largest eruption by volume in the Pleistocene, with no evidence of ill effects.

The "intensity of occupation" of archaeological sites naturally fluctuated for many reasons. In Paleolithic contexts, sites were almost never inhabited continuously. We usually don't know why a local population returned more often to a site, or why the later population may have used the site less often, but those changes in pattern will make a big difference to the occupation intensity. It's not enough to show that a fluctuation in occupation intensity was coincident with an eruption or climate event -- such coincidences are inevitable even when "occupation intensity" changed randomly.

What role volcanoes?

Bad things happened in the past. Many of those bad things -- megadroughts, volcanoes, asteroid impacts, flesh-eating bacteria -- probably killed a lot of people.

But our ability to find the effects of these death-dealing events is a lot more limited than you might assume. Less than a thousand years after the Black Death, how many signs of it are still evident today? To the exceedingly clever, who know where to look, there are a few. If we discount historical records, which do not exist for the Pleistocene, and limit ourselves to very small samples of bone and stone remains, it becomes very difficult to demonstrate this widespread epidemic, which reduced the population of some parts of Europe by up to half.

Most Paleolithic sites document exceedingly low-intensity use of an area by ancient people, and have gaps of thousands of years. The hope of finding a single event with a short duration is near zero, unless it affected many sites in the same way.

The extinction of a widespread group of hominids would be one kind of event we might test. In the current example, I think the data point to a clear conclusion: Not all Neandertals were killed, starved, or slowly declined due to the effects of any single volcanic eruption. Too many of them clearly survived the time of the large eruptions, and the available archaeological indicators suggest that their populations tended to recover after climate extremes had been reached. They were very resilient to climate change, more than many other mammals.

It's not possible to rule out that one or more eruptions may not have had important effects, even ones that may have devastated some local populations. This is possibly the case at Mezmaiskaya. Nor is it possible to exclude the hypothesis that climate changes of greater and greater amplitude may have stressed their populations, contributing to the Neandertal demise.

That's one of the returning frustrations of the archaeological record. An event might have been a major tragedy in human terms, but essentially invisible to us today. Meanwhile, the large-scale dynamics of human populations, including speciation and extinction, do not appear to fit the record of catastrophic eruptions. I don't see that as the end of the story, but a more interesting prologue to our understanding of ancient human dynamics.

UPDATE (2010-10-16): I received a note from Golovanova and Doronichev, kindly pointing out a serious error in my post. I had misread their paper -- I described it as supporting a coincidence of CI with the first ash evidence at Mezmaiskaya, but the paper clearly argues that the CI event was "coeval" with the second ash, in layer 1D of the site.

I have extensively updated the part of the post that refers to the CI eruption.

I'm skeptical that the CI and Kazbek ashfalls could have happened near the same time, because the latter seems by radiocarbon evidence to be 2000 or more years later than 40,000 years ago. But the ESR dates are arguably consistent with the idea that the two eruptions coincided. I wouldn't push a chronology argument very far, not without a list of calibrated radiocarbon and ESR/TL dates from the relevant eruptions. But the multiplicity of events helps to reiterate the basic point that geological events happened, and fluctuations of site intensity happened, and it will take a coincidence across many sites to correlate the two.

References

I wrote about Crete twice last month ("Crete: Pleistocene port of call?", "More tools from Crete"). Now John Noble Wilford writes about Strasser and Panagopoulou's work: "On Crete, New Evidence of Very Ancient Mariners". The article reviews the finds, and then gives space to a bunch of speculations.

The exposed uplifted layers represent the sequence of geologic periods that have been well studied and dated, in some cases correlated to established dates of glacial and interglacial periods of the most recent ice age. In addition, the team analyzed the layer bearing the tools and determined that the soil had been on the surface 130,000 to 190,000 years ago.

Dr. Runnels said he considered this a minimum age for the tools themselves. They include not only quartz hand axes, but also cleavers and scrapers, all of which are in the Acheulean style. The tools could have been made millenniums before they became, as it were, frozen in time in the Cretan cliffs, the archaeologists said.

Dr. Runnels suggested that the tools could be at least twice as old as the geologic layers. Dr. Strasser said they could be as much as 700,000 years old. Further explorations are planned this summer.

Ancient artifacts may be exposed to the elements once again and then re-incorporated into more recent sedimentary contexts, a process called "reworking". It happens. But it's a stretch, unless there is some independent evidence that the tools and surrounding rocks bear signs of battering from water transport or other contextual evidence of reworking.

Going out and saying that the tools could be "as much as 700,000 years old" is just overreaching -- it's like they're trying to say this is comparable to the "earliest" evidence of watercraft. And you really have to stretch the dates to get there: Flores was apparently inhabited by 800,000 years ago.

At the end:

But archaeologists and experts on early nautical history said the discovery appeared to show that these surprisingly ancient mariners had craft sturdier and more reliable than rafts. They also must have had the cognitive ability to conceive and carry out repeated water crossing over great distances in order to establish sustainable populations producing an abundance of stone artifacts.

Maybe. Maybe not. What evidence is there that the crossings were "repeated"? Imagine what would serve...finding Crete-derived rocks in a mainland site would do it, or vice-versa. Any evidence of transport. I don't imagine we'll find any earlier human-introduced fauna, and a human-induced extinction might result from a single invasion, not a "sustained" record of multiple crossings.

I pointed to one such faunal turnover in my last Crete post, which would point to a human invasion in the mid-Middle Pleistocene. Parallel technical change with Greece or North Africa after this time would show multiple contacts -- but such evidence would suppose a long archaeological record that we don't yet have.

I just don't think it helps to speculate so freely. Sure, we might find things that surprise us. But the actual facts are surprising enough to justify funding much more work.

Bruce Bower reports on excavations by Thomas Strasser on the Mediterranean island of Crete: "Ancient hominids may have been seafarers".

At Preveli Gorge, Stone Age artifacts were excavated from four terraces along a rocky outcrop that overlooks the Mediterranean Sea. Tectonic activity has pushed older sediment above younger sediment on Crete, so 130,000-year-old artifacts emerged from the uppermost terrace. Other terraces received age estimates of 110,000 years, 80,000 years and 45,000 years.

These minimum age estimates relied on comparisons of artifact-bearing sediment to sediment from sea cores with known ages. Geologists are now assessing whether absolute dating techniques can be applied to Crete’s Stone Age sites, Strasser says.

I would set a high bar for evidence on this one. No details are available; it was a conference presentation.

One possibility: According to Alexandra van der Geer and colleagues (2006), there was a faunal turnover on Crete 300,000 years ago. The earlier fauna included a 1.5-meter dwarf mammoth and dwarf hippos. The hippos were hoof-walkers apparently adapted to a "more terrestrial" activity pattern. Sometime after 400,000 years ago, this fauna was replaced. No more hippos or mammoths, and new, larger, mainland-derived elephants. As they wrote (125):

The dwarf elephant may be large compared to the mammoth of the previous period, but it is still about 30% smaller than its mainland ancestor E. antiquus, which has a shoulder heigth of 3.7 m. The dwarf elephant has strongly curved tusks. It is still a matter of debate why this elephant did not reach a pygmy size.

The arrival of humans is one possibility. Sondaar and van der Geer (2002) suggested that Sardinia-Corsica might have undergone similar turnovers induced by human arrivals during the Middle and Late Pleistocene.

But that's entirely speculation. I want to see some dating and good descriptions of the artifacts and their context.

If the artifacts found by Strasser represent a genuine occupation, the Cretans would presumably have been seafaring Neandertals. Or Preneandertal-derived hobbits. Man, I wish I'd made that one of the 2010 predictions!

References:

van der Geer A, Dermitzakis M, de Vos J. 2006. Crete before the Cretans: The reign of dwarfs. Pharos: Journal of the Netherlands Institute in Athens 13:119-130.

Sondaar PY, Van der Geer AAE 2002. Plio-Pleistocene terrestrial vertebrate faunal evolution on Mediterranean islands, compared to that of the Palearctic mainland. Annales Géologiques des Pays Helléniques 1e Série 39, A: 165-180.