Anthropology.net

Synchronous extinction of North America’s Pleistocene mammals — PNAS

Following on from my recent post regarding the apparent lack of evidence for a Clovis comet, I want to address this recent paper by J. Tyler Faith, in which he and his fellow authors offer statistical evidence to suggest that the mammalian extinction event at the very end of the Pleistocene largely took place between 12 kya and 10 kya.

I had originally intended to review this paper alone, but after only a cursory amount of reading around, it soon became clear I needed to address some of the other research into this mysterious time, without recourse to an extraterrestrial impact to explain the sudden disappearance not only of large bodied mammals, but also significant numbers of birds at the same time, an anomaly that cannot be explained away simply by inferring overkill of mammals by human predators, hyperdisease or climate change as the main agents of destruction.

Rather than try to offer a specific answer to this massive extinction question of my own, I have instead attempted here to include consideration of a range of factors and circumstances over a longer period of time and from further afield (in Eurasia) to help explain the unique context in which the American extinctions took place. For reasons of necessitated brevity, I have in some cases only referred in passing to some papers, most of which are open access.  But suffice it to say, all these papers are worth reading in their entirety, if only to emphasize the idea that there is probably an intricate network of causal complexity that best accounts for the North American terminal extinction event, rather than a single, albeit spectacularly compelling cause that now as in the past,  is notable for its extremely elusive nature, and which in all likelihood, doesn’t actually exist.

This paper, by Faith et al, addresses the long-standing debate surrounding the timing of the megafaunal extinction event in the terminal Pleistocene, and in so doing trying to identify the contributory factors that led to the demise of 31 genera of fauna at that time. Here’s the abstract:

The late Pleistocene witnessed the extinction of 35 genera of North American mammals. The last appearance dates of 16 of these genera securely fall between 12,000 and 10,000 radiocarbon years ago (13,800–11,400 calendar years B.P.), although whether the absence of fossil occurrences for the remaining 19 genera from this time interval is the result of sampling error or temporally staggered extinctions is unclear. Analysis of the chronology of extinctions suggests that sampling error can explain the absence of terminal Pleistocene last appearance dates for the remaining 19 genera. The extinction chronology of North American Pleistocene mammals therefore can be characterized as a synchronous event that took place 12,000–10,000 radiocarbon years B.P. Results favor an extinction mechanism that is capable of wiping out up to 35 genera across a continent in a geologic instant.

In particular Faith et al set out to answer the question of whether it was an event drawn out over many millennia or one that involved simultaneous extinctions in the terminal Pleistocene  – with the implication that if this was a  staggered event there may be a gradual change in the environment that was the cause, whereas a for sudden event, one or more extraordinary explanations need to be sought.

Indeed, they conclude that their statistical models indicate the latter scenario, although other (undefined) scenarios were possible, with some extinctions – between 0 and 8 genera -  taking place prior to 12 kya, and that further the idea of comet strike or human hand are generally considered to be two of the most likely of an unknown number of as yet inconclusive theories that might have contributed to this simultaneous extinction event.

The authors propose that sampling error may account for the lack of information, concluding that two main causes might be responsible for the disappearance of these animals in the space of two thousand years, roughly equating to between 12 kya and 10 kya – an extraterrestrial impact, or overkill by humans. As noted elsewhere, the Last Apppearance Date for a species in the fossil record, doesn’t necessarily mean that every single animal had died by then, but that numbers may have been so reduced as to make them  ‘palaeontologically invisible’ but they were still in effect, extinct as a viable population – this invisibility is something that may turn out to be relevant to the question of credibly identifying a very early pre-Clovis human presence in the Americas, especially when addressing some of the claims of 50 kya, from sites such as Topper, and 40 kya from Mexico and Baja California.

However, as we have seen, and assuming the recently published data are correct, there is at present very little if any substantive geochemical evidence for a comet or asteroid strike. And as has been noted previously, it’s hard to imagine there were enough humans on the ground in Pleistocene America to effect such a widespread die off, regardless of whatever lithic technology they deployed – or even that they would deliberately have killed order of magnitudes more animals than they could eat or would have needed to process into manufactured artefacts, such as clothing from hides or utensils from teeth, ivory, sinews and gut etc.

The researchers used two simulations to assess the synchronous extinction theory, the first of which is referred to as the continental simulation, described thus:

In our first simulation, referred to as the continental simulation, each of the 1,955 stratigraphic occurrences are assigned randomly a pre- or post- 12,000 radiocarbon years B.P. date based on the observed relative frequency of terminal Pleistocene taxon dates in the fossil record (3.4% for the complete set of radiocarbon dates and 1.3% when excluding radiocarbon dates of intermediate reliability). For each of 10,000 iterations, the number of genera receiving a terminal Pleistocene taxon date is calculated. All of the 31 genera included in the analysis are assumed to survive to the terminal Pleistocene, and all occurrences are assumed to be equally likely to receive a terminal Pleistocene taxon date.

The continental simulation essentially estimates how many genera that we can expect to recover from the terminal Pleistocene if all of them had survived to that time, given the empirically derived probability of observing a terminal Pleistocene fossil occurrence. We ran two separate trials of the continental simulation, both including and excluding radiocarbon dates that received intermediate evaluation scores (30).

Next they describe their biogeographic simulation:

Our second simulation, referred to as the biogeographic simulation, recognizes that the extinct Pleistocene genera were not distributed uniformly across the continental United States and that some regions are more likely to provide a terminal Pleistocene taxon date than others. For example, the distribution of Hydrochoerus and Holmesina within the U.S. is limited to the southeast (28), an area that yields relatively few terminal Pleistocene taxon dates (Table S4).

Because of their biogeographic ranges, these taxa are less likely to have been recovered from terminal Pleistocene deposits if they had survived to that time. This issue is addressed in our biogeographic simulation, which recognizes seven physiographic zones within the continental United States (31) (Fig. 2). In this simulation, the stratigraphic occurrences of a given genus are assigned randomly to a physiographic zone based on its relative abundance in that region (Table S4). In turn, the probability that a simulated occurrence will be assigned a terminal Pleistocene taxon date is based on the relative frequency of terminal Pleistocene fossil occurrences known from that zone (Table S4). For each of 10,000 iterations, the number of taxa receiving a terminal Pleistocene date is calculated. The biogeographic simulation also explores the possibility of preterminal Pleistocene extinctions.

To do so, we prohibited between 0 and 15 randomly selected genera from receiving a terminal Pleistocene taxon date over 16 separate trials of 10,000 iterations. The biogeographic simulation estimates how many taxa that we can expect to recover from the terminal Pleistocene if anywhere from 16 to 31 genera had survived to that time. As with the continental simulation, we ran two trials of the biogeographic simulation, once using all of the terminal Pleistocene taxon dates and once excluding radiocarbon dates of intermediate reliability (30).

The authors conclude that all their models can be interpreted as being in accordance with an abrupt event at the end of the Pleistocene, although in contrast to the two previous papers, they contend that a cometary impact may have been one of four main options for consideration as a contributory factor – some of the others being overkill by humans, hyperdisease and climate change.

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In recent years a theory has emerged that seeks to explain three mysterious events that took place at around 13,000 years ago (kya) – the sudden cooling phase known as the Younger Dryas, at the end of the Bølling Allerød warm interstadial,  the sudden termination of the Clovis culture in North America, along with the mass extinction event there that saw the demise of over 30 genera of Pleistocene fauna, although this last event had been in progress from c.40 kya, and also affected further flung parts of the world such as Eurasia and Australia. (I’ll address this last point more fully in a forthcoming post ).

Previous theories postulated that a complex mix of terrestrial – albeit not clearly defined – factors had been responsible for these catastrophic events, which were viewed as having had separate causes, but were especially devastating because of their combined synchronicity.

Following research at numerous archaeological sites, notably by Firestone, West and Kennett, (open access paper), it was proposed that around this time a comet either hit the planetary surface, possibly on the Laurentide ice sheet, or exploded in mid air, initially causing widespread and ferocious burning, followed by a prolonged period of plunging temperatures which laid waste to the North American landscape, killing off much of the fauna, including humans, who had survived the primary fireball, in what has been proposed to have been a period akin to a nuclear winter.

Evidence cited in support of this idea included raised levels of iridium and the presence of nano-diamonds on the ground, both of which are identified as markers for an extraterrestrial impact, as well as a so-called ‘black mat’, a carbon rich layer plainly visible in various archaeological trenches across numerous sites contemporaneous with these events.

More recently, two teams of researchers set out to evaluate the evidence, both of whose findings cast serious doubt on the comet theory, but leave unexplained the presence of nano-diamonds,with one team suggesting that if a cometary impact was responsible, the comet itself must have been radically different from anything currently known to science.

Two papers have been published at PNAS, and I’ll attempt to convey their import here – my thanks go to both teams for very kindly forwarding me copies of the full texts, (which currently reside behind comet-proof paywalls) so without further ado, here they are. First we have ‘Absence of Geochemical Evidence for an Impact Event at the Bølling Allerød/Younger Dryas Transition’, by François Paquay, a Doctoral graduate student in the Department of Geology and Geophysics at the University of Hawaii at Manoa (UHM), and his team, from which this is the abstract:

High concentrations of iridium have been reported in terrestrial sediments dated at 12.9 ka and are interpreted to support an extraterrestrial impact event as the cause of the observed extinction in the Rancholabren fauna, changes in the Paleoindian cultures, and the onset of the Younger Dryas cooling [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104:16016–16021]. Here, we report a platinum group element (PGE: Os, Ir, Ru, Rh, Pt, Pd), gold (Au) concentrations, and 187Os/188Os ratios in time-equivalent terrestrial, lacustrine, and marine sections to seek robust evidence of an extraterrestrial contribution.

First, our results do not reproduce the previously reported elevated Ir concentrations. Second, 187Os/ 188Os isotopic ratios in the sediment layers investigated are similar to average crustal values, indicating the absence of a significant meteoritic Os contribution to these sediments. Third, no PGE anomalies distinct from crustal signatures are present in the marine record in either the Gulf of California (DSDP 480, Guaymas Basin) or the Cariaco Basin (ODP 1002C). Our data show no evidence of an extraterrestrial (ET)-PGE enrichment anomaly in any of the investigated depositional settings investigated across North America and in one section in Belgium. The lack of a clear ET-PGE signature in this sample suite is inconsistent with the impact of a large chondritic projectile at the Bølling–Allerød/Younger Dryas transition.

As we can see, the original intention of this research was to confirm the comet theory by looking again at the evidence, but as is made clear throughout the paper, that confirmation simply failed to materialise. They examined the layer beneath the ‘black mat’, noting a lack of characteristic markers such as ‘shocked minerals, spherules composed of glass (or its alteration products), or Ni-rich spinels‘.

Observing further that anomalously elevated iridium levels alone don’t necessarily confirm an extraterrestrial impact, whereas other elements present stronger evidence. Analysis of Platinum Group Elements (PGEs) combined with Osmium (Os) isotopic samples revealed that the high levels of iridium (Ir) reported at sites were not confirmed by the authors’ own analytical process. This from the paper:

The PGE abundances for Murray Springs (AZ), Blackwater Draw (NM), Howard Bay (NC), Lake Lubbock (TX), Topper (SC), and Lommel (Belgium) sections are presented in Table S1. From these same sections, but on a different powder split, a comparison of 187Os/188Os, Os concentrations and Os/Ir ratios in different depositional settings is also given (Table S1; see also Table S2).

Firestone et al. (22) have reported 169 measurements of Ir at 14 sites up to 9,200 km apart in the 14C-dated BA/YD (see Fig.S1) bulk sediments, magnetic fraction, and the black mat, but not in the over- and underlying layers. In 5 of the 12 sites reported in table 1 in ref. 22, the Ir concentrations in the bulk sediment are 0.5 ng/g, and the concentrations in four sites (Murray Springs, Blackwater Draw, Lake Hind, and Carolina Bays, Max) reach 2.3–3.8 ng/g Ir. These values are comparable to those obtained at a number of KT boundary sites (e.g., 3.7 ng/g in Petriccio, Italy; 0.85 ng/g in Brazos River, TX; 5.7 ng/g in Beloc, Haiti; 2.9 ng/g in Frenchman River, Canada; and 1.4 ng/g in Hell Creek, MT (37). The Ir concentrations in the magnetic fractions of four samples (22) (Blackwater Draw, Wally’s Beach, Lommel, and Carolina Bay, Max) show concentrations between 15 and 117 ng/g [i.e., 25% of CI chondrites, Ir  460–472 ng/g; (38, 39)].

The data presented by Firestone et al. (24) also show a clear inverse correlation between Ni and Ir (Fig. S2A). This is rather unusual as Ni and Ir are both siderophile elements, enriched in meteorites compared to the terrestrial crust. Both elements typically show the same geochemical behavior during a meteorite impact on the terrestrial crust. In numerous crater impact sites such as Popigai (40) Lapparja¨vi (41), Morokweng (42), Clearwater East (43) and at the KT boundary (25), Ir and Ni display a positive correlation (Fig. S2B).

Table S1 shows that the new analyses do not confirm the elevated Ir values published by Firestone et al. (24). The PGE concentrations measured in bulk sediments are lower by at least an order of magnitude or more. Nugget effects, which cause small-scale inhomogeneities in PGE distribution and account for a variability of concentrations in geological samples (44–46), can be fully discarded here. The use of samples 10 g precludes any nugget effect and has been demonstrated to lead to good sample reproducibility (40), confirmed by repeated analyses in this study.

The authors further claim that all samples from the Younger Dryas black mat exhibit levels considered average for continental crust, whilst the sites at Murray Springs and Blackwater Draw may have shown higher levels of osmium and iridium as a direct result of the black mat’s formation process.

Moving next from land to sea, the team examined levels of osmium isotopes present in the ocean – previous research at Chicxulub  at the KT boundary (the end of the Cretaceous 65 mya – (but check this)) showed that when high levels of osmium borne on an extraterrestrial impactor entered the ocean, the Os isotopic ratios fell. To test the comet theory, two marine environments were analysed, the Gulf of California and the Cariaco Basin, located off Venezuela. The osmium isotope values in the Gulf of California were significantly higher than those in the Cariaco Basin, indicating the lack of cometary input, whilst the lower values detected in the latter did not correspond with the timing Younger Dryas, prompting the conclusion that there was no evidence for a ‘large chondritic impact event’ that had affected the ocean in the predicted manner.

Before heading back on to dry land for the discussion, it’s worth taking a quick look at the Cariaco Basin, as its unusual properties mark it apart from the average stretch of ocean, presumably making it an ideal model for this study, as this link to the CARIACO project explains.

Broadly speaking, the first part of the discussion reiterates and expands upon the osmium isotope studies in seawater, the lack of increased Platinum Group Elements that should be present on land in the wake of an impact, as well as normal levels of iridium found in Greenland ice cores. From there we move on to those mysterious nano-diamonds, an integral component in the comet theory, but which in the context of this paper, appear to be the true anomaly in this saga.

As we have seen, a cometary impact of the types with which we are familiar, should have left both a nano-diamond and PGE signature, but all we have are the nano-diamonds. This in turn causes the authors to speculate upon the properties of a putative comet, as we see:

Results presented here show that it is unlikely that the nanodiamonds were derived from any known meteoritic projectile, in contrast to suggestions of a swarm of comets or carbonaceous chondrite (26). Specifically, mass balance calculations show that if all of the nanodiamonds in the BA/YD sections are primary meteoritic material (1,500 ppm of the bulk; (75) (covering a fluence of 30% of Earth’s surface) (Fig. S1), and were not formed upon surface impact, a chondritic projectile of 1.2 km in diameter should produce an Ir fluence of 1 ng/cm2 that is clearly missing based on our results. For clarity, we emphasize that PGE and Os isotope data are sensitive indicators of undifferentiated meteoritic material.

Alternatively, to avoid PGE enrichment, it is possible to invoke the impact of one or several differentiated, PGEs-poor, possibly still unknown type of achondritic meteorites that vaporized in Earth’s atmosphere at the BA/YD transition is one possibility. However, the probabilities of the arrival of this type of projectile to Earth is low (www.unb.ca/passc/ImpactDatabase/), and this type of bolide lacks all allotropes of nanodiamonds.

In the case of one or several surface impact(s) of achondritic projectile(s), which could explain the absence of PGEs in the studied BA/YD sections, it becomes difficult to explain the formation of nanodiamonds without a well-dated surface expression of one or several craters. So far, no BA/YD craters are yet known. Based on the existing distribution of terrestrial craters (76), one or several large craters of this very young age cannot be eroded, filled with younger sediments or erased by subduction.

Most likely such fresh impact crater(s) would have been found and confirmed many years ago. In the scenario of a 1- to 2-km diameter achondritic, PGEs-poor projectile exploding into the atmosphere or hitting only the Laurentide Ice Sheet, a crater would possibly not have been formed. However, in this case, a source of carbon is required to form the recovered lonsdaleite crystals, and the concentration of carbon in this type of meteorites is extremely low. It is possible that the nanodiamonds were formed during an airburst, but it does not explain the absence of a geochemical anomaly.

Therefore, a strong decoupling of PGEs and nanodiamonds exists which differs from other known impact events. The occurrence of high concentrations of cubic diamonds and nanodiamonds (1,340 ppb) (24) in multiple BA/YD sections, found within carbon spherules without an associated defined geochemical anomaly, is therefore not a robust diagnostic of an impact event.

Thus we have something of a mystery  – although other research has called the impact event into question, none as far as I’m aware appear so thoroughly to confound the idea as this paper. There remains however the question of what exactly created the nano-diamonds, and whether that agency was from outer space or terrestrial in origin, plus the vague possibility that the Earth was indeed hit by something whose precise nature and identity continue to elude us.

I had intended to cover another, related paper in this post, but rather than relegate it to the end of this one, I think it best to write it up separately, especially as it focusses more on the micro-spherules, or lack thereof, alluded to earlier in this post. And suffice it to say, there is a great deal more information in the reviewed paper, especially in the guise of graphs and graphics which I haven’t included here, and I’d be happy to forward a copy to anyone interested in looking at this research in greater detail.

François S. Paquay will be appearing next week at the Fall 2009 meeting of the American Geophysical Union

image from: Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling – Firestone et al, PNAS

see also: Press Release

Reassessing the Source of Long-Period Comets – by Nathan A. Kaib, Thomas Quinn

Topper Site

The Berkeley Laboratory Isotopes Project

Periodic Table

Reference: Absence of Geochemical Evidence for an Impact Event at the Bølling Allerød/Younger Dryas Transition, by François Paquay, Greg Ravizza (also from UHM), Steven Goderis and Philippe Claeys from Vrije Universiteit Brussel, Frank Vanhaeck from the Universiteit Ghent, Matthew Boyd from Lakehead University, Todd A. Surovell from the University of Wyoming at Laramie, and Vance T. Holliday and C. Vance Haynes, Jr. from the University of Arizona at Tucson.

www.pnas.org/cgi/doi/10.1073/pnas.0908874106 (correct link will be posted when available).

As mentioned previously, the Royal Society are celebrating 350 years of publication, and in recognition of this they are offering free access to a vast number of papers, both past and present – indeed the current edition of the Proceedings of the Royal Society B (Biological Sciences) treats us to a Special Issue ‘Recent advances in Chinese palaeontology,’ organized and edited by Xing Xu, Zhe-Xi Luo and Jia-Yu Rong. As well as what appears to be a whole slew of interesting articles discussing an impressive array of fossils dating all the way back to the Cambrian, the final article concerns one of our more direct ancestors, in the guise of Homo erectus.

Here’s the abstract:

A new Homo erectus endocast, Zhoukoudian (ZKD) V, is assessed by comparing it with ZKD II, ZKD III, ZKD X, ZKD XI, ZKD XII, Hexian, Trinil II, Sambungmacan (Sm) 3, Sangiran 2, Sangiran 17, KNM-ER 3733, KNM-WT 15 000, Kabwe, Liujiang and 31 modern Chinese. The endocast of ZKD V has an estimated endocranial volume of 1140 ml. As the geological age of ZKD V is younger than the other ZKD H. erectus, evolutionary changes in brain morphology are evaluated. The brain size of the ZKD specimens increases slightly over time.

Compared with the other ZKD endocasts, ZKD V shows important differences, including broader frontal and occipital lobes, some indication of fuller parietal lobes, and relatively large brain size that reflect significant trends documented in later hominin brain evolution. Bivariate and principal component analyses indicate that geographical variation does not characterize the ZKD, African and other Asian specimens. The ZKD endocasts share some common morphological and morphometric features with other H. erectus endocasts that distinguish them from Homo sapiens.

I’ll just add a few brief notes from the paper, starting with the age of the fossil ZKD V – it was originally dated to c. 230 kya, (kya = thousands of years ago) but more recent research has pushed back the date to something between 400 kya – 500 kya, “using ²⁶Al/¹⁰Be on buried quartz sediments and lithic artefacts from layers 7–10″.

This aluminium/beryllium isotopic dating  technique was in the news earlier in 2009 when it was revealed that the oldest occupants of the site may have lived as long ago  as 680,000 – 780,000 years ago, some 200 ky earlier than previous dating analyses had suggested, and further that they may have been specifically adapted to a cold climate.

The component fragments of the ZKD V skull were recovered in two separate excavations, the first of which took place in 1934 and the second in 1966. Here are details of other remains that were used in comparison to ZKD V from the paper:

Weidenreich (1935, 1943) studied the craniums of ZKD II, III, X, XI, XII and the portions of ZKD V that were then available. He suggested that the fundamental morphology of the ZKD crania remained unchanged over time. When Qiu et al. (1973) were able to study the more complete ZKD V cranium, they determined that it not only has the typical ZKD morphological characters, but also that it has what they described as more progressive features. For instance, the skull of ZKD V has a high and round temporal bone, a reduced occipital torus, and a short distance between inion and the internal occipital protuberance. Other evidence for temporal variation in ZKD H. erectus derives from studies of the human teeth (Zhang 1991) and the lithic industry (Pei & Zhang 1985).

In this paper, we analyse an unpublished endocranial cast of the ZKD V specimen and compare it with other H. erectus (ZKD II, III, X, XI, XII, Hexian, Sambungmacan (Sm) 3, Trinil II, Sangiran 2, Sangiran 17, KNM-ER 3733, KNM-WT 15 000) and Homo sapiens (Kabwe from Zambia, Liujiang from China, and a comparative modern Chinese sample). Our objective is to facilitate a more comprehensive understanding of ZKD H. erectus brain morphology and to re-examine the variability of H. erectus.

There foll0ws a more detailed discussion of the gross morphology of ZKD V, compared with cranial features of the other specimens in the study, whilst the section on bivariate morphometric analysis offers more in the way of specific measurement and statistical considerations.

Finally, a word or two on the overall context of ZKD V and its correlation to other specimens for Asia and Africa:

The taxonomic affinity of the ZKD hominins has long been questioned. Previous analyses, mostly based on study of external cranial morphology, led researchers to propose that the ZKD crania possess unique morphological and morphometric features distinguishing them from other Asian as well as African hominins (Kidder 1998; Anton 2002, 2003; Kidder & Durband 2004). According to Anton (2002), regional differentiation exists between northern Asian and southeast Asian H. erectus, and the ZKD H. erectus sample exhibits less variation than the early Indonesian sample. Other researchers argue that the cranial features thought to define Asian H. erectus are also expressed on some African specimens (Rightmire 1998). Differences between the Far Eastern and African hominins are viewed as minor and not indicative of more than one species (Braüer 1994).

Detailed endocast studies comparing Asian and other H. erectus specimens are limited in number. Begun & Walker (1993) suggested that the ZKD H. erectus endocasts are overall morphologically similar to KNM-WT 15 000. In a previous study, we found that Hexian from central-eastern China is morphologically most similar to the ZKD specimens (Wu et al. 2006). Interestingly, the nine-variable and six-variable PCA results of this study show that the six ZKD endocasts do not cluster together, and do not present a different pattern from the African or the other Asian specimens. Our research on endocast size and shape provides no support for the argument that ZKD H. erectus or other Asian H. erectus specimens represent a morphologically distinct species…

…Our studies indicate that the ZKD endocasts share some morphological and morphometric features with the African and other Asian specimens that distinguish them from the modern Chinese comparative sample. We also note that the ZKD V endocast shows some progressive features compared with the other ZKD H. erectus— ‘progressive’ in the sense that ZKD V differs in ways that foreshadow the greater overall brain height and fuller lobes that generally characterize H. sapiens. This is not unexpected given its later geological age and the possibility that as much as half a million years may be represented by the ZKD sample.

In conclusion, the researchers appear  convinced that African and Asian erectus specimens conform to a single African origin theory, although I suspect that others in the field will find sufficient detail in the data that suggest a far more complex aspect to this era of human evolution.

image: Reconstructed skull and endocast of ZKD V: (a(i)(ii)) superior view; (b(i)(ii)) left lateral view; (c(i)(ii)) anterior view; (d(i)(ii)) right lateral view; (e(i)(ii)) basal view; and (f(i)(ii)) posterior view. Reconstructed areas are shown in black. Scale bar, 4 cm.

Reference: A New Homo erectus (Zhoukoudian V) Brain Endocast From China, by Xiujie Wu1, Lynne A. Schepartz and Wu Liu, Published online before print April 29, 2009, doi: 10.1098/rspb.2009.0149 Proc. R. Soc. B  22 January 2010   vol. 277  no. 1679  337-344

Thanksgiving is now well and truly over, as are the lives of numerous birds, in this case turkeys, that were consumed as part of the tradition, whilst even larger quantities of this particular bird are slated for slaughter and consumption as Christmas once more raises its ominous spectre on the festive horizon. I’m not sure for how long the consumption of birds has been a main feature of human feasting occasions, but as we see from the linked paper, humans have been eating various species of bird for hundreds of thousands of years, which is surprising in the context of how difficult it must have been for our ancestors to acquire this food item with what we might consider to be comparatively limited technological prowess. Two aspects of this study particularly interested me, the first that archaic humans were able to acquire avian prey, and second that on many occasions, it appears that the acquired meat may have been eaten in its raw state. Whether it was eaten by humans or given to other animals such as tamed hunting birds is something I’ll address in due course.

As we have seen in previous posts, there are numerous caves and rock-shelters across Spain which offer a wealth of finds and associated data, affording us invaluable insights into the life-styles of ancient humans, particularly when it comes to trying to ascertain which prey animals were hunted and consumed in the Middle Pleistocene.

As the authors Blasco and Fernández Peris note in their paper, much attention on this subject is paid to larger prey animals and the ways in which they were hunted, butchered and consumed, whilst the data from smaller prey comes under less scrutiny. In this paper they show how that around 150k years ago, archaic humans such as Homo heidelbergensis or possibly Homo neanderthalensis consumed, Aythya sp. a type of marsh-dwelling duck, although the birds themselves may on occasion have been eaten raw. How these birds were actually caught remains for now an open question, but we can be fairly sure that advanced hunting skills would have been necessary in order for this prey to have been a regular feature on the menu, assuming the birds weren’t opportunistically scavenged.

Here’s the abstract of the paper that’s behind a paywall, but because author Ruth Blasco has very kindly forwarded me a copy, I’m pleased to be able to offer more comment than might otherwise have been the case:

Abstract:

The consumption of small prey dates back to the Plio-Pleistocene chronologies in some African sites. However, the systematic acquisition and consumption of small prey in the pre-Upper Palaeolithic times is still a highly debated topic in Europe. Although the utilization of leporids has been recorded in several pre-Late Pleistocene European sites, the evidence of bird consumption is not as common for these periods. Nevertheless, Level XI (MIS 6) of Bolomor Cave has clear diagnostic elements to document the acquisition and use of birds (Aythya sp.) for food in the form of: (1) cutmarks on bones of both the front and hind limb; (2) presence of burning patterns on the extremities of the bones (areas of the skeleton with less meat); and (3) human toothmarks on limb bones.

The capture of birds is classified as quick-flying game in the archaeological sites. The acquiring of fast-running (mostly lagomorphs) and quick-flying small prey requires a sophisticated technology and involves obtaining and processing ways different from those used for large- and medium-sized animals. From this perspective, the aim of this paper is to examine possible patterns in the processing sequence of birds from Level XI of Bolomor Cave and to improve the data on their butchery and human consumption in the Middle Pleistocene of Iberian Peninsula.

The introduction goes on to discuss how avian prey may have been overlooked as a contributory factor to ancient humans as the amount of energy derived from their consumption is obviously much less than sources of meat on the hoof. Moreover, because the processing and consumption of smaller prey require little or no use of stone tools, as hands and teeth can be effectively deployed, less evidence of lithic activity appears on the bones of those birds that were eaten. However, as the authors note, other evidence in the guise of tooth-marks, breakages and alteration by fire of bird bones can serve equally well as clues that such remains found at ancient sites were there as a result of human activity rather than from the activities of other scavenging animals, birds of prey, or death by natural causes at the site in question.

Details of previous research at other sites is given here:

So far, the older evidences on avian remains were identified in the Early Pleistocene of Sima del Elefante (Spain) (Huguet, 2007) and of Dursunlu (Turkey) (Gu¨ leç et al., 2009). At the Sima del Elefante site, one cutmark on a proximal metaphysis of a large sized-bird radius was observed at Level TE9a. In Dursunlu, several incisions on distal metatarsus of a large bird were also documented. In more recent chronologies, an anthropogenic use on Pyrrhocorax graculus bones was suggested in the ‘‘acheulean cabin’’ of the Lazaret in France (Bouchud, 1969).

This study was based on the spatial distribution of the bird remains, which are more abundant inside the cabin. Nevertheless, this distribution has been the subject of debate. According to Villa (1983), this phenomenon is due to the natural formation process at Level V of the site. Some species, such as crows and pigeons, are known to nest on the wall of the caves and their bones are frequently found in karstic contexts. It is possible that some of these birds died from natural causes and others may have been brought by birds of prey (Bubo bubo) in form of pellet or by carnivores (Vulpes vulpes, Felis silvestris or Lynx spelaea) that occasionally inhabited the cavity (Lumley et al., 2004).

However, cutmarks on one Columba livia right humerus have been identified at UA 25 of Lazaret cave (Lumley et al., 2004; Roger, 2004). On the other hand, the bird accumulations in the Middle Pleistocene of the A´ ridos site (Spain) were interpreted by Mourer-Chauvire´ (1980) as the result of human hunting. However, the avian skeletal representation of this site is not biased (Mourer-Chauvire´ , 1980) and therefore, the interpretation of bird accumulation by hominids could be problematic. In these cases, the identification of other diagnostic elements of anthropogenic processing on skeletal remains should be considered….

…In Bolomor Cave, the consumption of small prey is common throughout the entire stratigraphic sequence. At this site, cutmarks on leporid bones (Oryctolagus cuniculus) are documented repeatedly from MIS 9 to MIS 5e (Blasco, 2006; Sanchis Serra and Ferna´ndez Peris, 2008). Anthropogenic processing marks are also observed on tortoise remains (Testudo hermanni) at Level IV (Blasco, 2008) and on one swan humerus (Cygnus olor) at Level XII (Blasco, 2006). This paper aims to add available data on the consumption and butchery of birds at Level XI in Bolomor Cave. Level XI is one of the levels, within the stratigraphic sequence of the site, which presents the highest percentage of very small sized animals in relation to ungulates and allows us to examine possible patterns of bird consumption.

As Cova de Bolomor might not be familiar to all, a brief word on its location and archaeological history is in order. The cave itself is faces north east, and is located on Monduver Mountain in the Valldigna Valley, near the town of Tavernes, Valencia in eastern Spain. Described as a karstic rock shelter, the site opened up around 500k years ago, and thus far, 17 archaeological levels have been identified, indicating numerous human occupations, where fossil remains, stone tools and hearths testify to activities that took place there.

As we see from an article in El Pais back in 2007, Neanderthal remains dating to 130k years ago have been found in the levels above XI, and comprise a milk tooth, an adult tooth and a partial skull, whilst other faunal remains indicate that animals such as macaque monkeys, rhinoceros and hippopotamus shared the immediate neighbourhood. The Neanderthal remains had been in the local museum since 1982, encased in a chunk of rock. As far as I can tell,  Bolomor was known to be of archaeological interest since the 19th century, but nevertheless the site suffered considerable damage in the 1930s, when explosions from nearby quarrying activities caused lumps of rock from the shelter to be scattered in the vicinity, which in turn were collected and taken to the museum for study and research.

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A new paper by Martin A.J. Williams et al, on the Mount Toba eruption 73,000 years ago, proposes that the destructive aftermath of the event caused widespread de-forestation in India, some 3,000 miles distant from Sumatra, the island on which the volcano was located. Here’s the abstract of that paper which is behind a paywall, but commented upon in Science Daily, to which I’ll refer shortly:

Abstract

The cooling effects of historic volcanic eruptions on world climate are well known but the impacts of even bigger prehistoric eruptions are still shrouded in mystery. The eruption of Toba volcano in northern Sumatra some 73,000 years ago was the largest explosive eruption of the past two million years, with a Volcanic Explosivity Index of magnitude 8, but its impact on climate has been controversial. In order to resolve this issue, we have analysed pollen from a marine core in the Bay of Bengal with stratified Toba ash, and the carbon isotopic composition of soil carbonates directly above and below the ash in three sites on a 400 km transect across central India.

Pollen evidence shows that the eruption was followed by initial cooling and prolonged desiccation, reflected in a decline in tree cover in India and the adjacent region. Carbon isotopes show that C3 forest was replaced by wooded to open C4 grassland in central India. Our results demonstrate that the Toba eruption caused climatic cooling and prolonged deforestation in South Asia, and challenge claims of minimal impact on tropical ecosystems and human populations.

The story is taken up by Science Daily,  in Supervolcano Eruption In Sumatra Deforested India 73,000 Years Ago, where the sheer scale of the event is reflected in this description of the eruption and the site itself:

The volcano ejected an estimated 800 cubic kilometers of ash into the atmosphere, leaving a crater (now the world’s largest volcanic lake) that is 100 kilometers long and 35 kilometers wide. Ash from the event has been found in India, the Indian Ocean, the Bay of Bengal and the South China Sea.

The bright ash reflected sunlight off the landscape, and volcanic sulfur aerosols impeded solar radiation for six years, initiating an “Instant Ice Age” that — according to evidence in ice cores taken in Greenland — lasted about 1,800 years.

During this instant ice age, temperatures dropped by as much as 16 degrees centigrade (28 degrees Fahrenheit), said University of Illinois anthropology professor Stanley Ambrose, a principal investigator on the new study with professor Martin A.J. Williams, of the University of Adelaide. Williams, who discovered a layer of Toba ash in central India in 1980, led the research.

The report then goes on to comment on the debate that has sprung up surrounding the idea that this event nearly wiped humanity off the face of the planet, causing a putative genetic ‘bottleneck’ event, whereby the diversity of the human gene pool was dramatically reduced, prompting some researchers to contend that the anatomically modern human population immediately after Mount Toba may have numbered only about 15,000 individuals. This idea has however been contested, most notably in a 2007 paper by Michael Petraglia et al, in which it is suggested that Middle Palaeolithic technology appears to have continued across the region without significant interruption, following investigations at the site of Jwalapuram.

The Science Daily report also gives details of how Williams and his team were able to deduce the climatic impact of the eruption, as we see from this:

To address the limited evidence of the terrestrial effects of Toba, Ambrose and his colleagues pursued two lines of research: They analyzed pollen from a marine core in the Bay of Bengal that included a layer of ash from the Toba eruption, and they looked at carbon isotope ratios in fossil soil carbonates taken from directly above and below the Toba ash in three locations in central India.

Carbon isotopes reflect the type of vegetation that existed at a given locale and time. Heavily forested regions leave carbon isotope fingerprints that are distinct from those of grasses or grassy woodlands.

Both lines of evidence revealed a distinct change in the type of vegetation in India immediately after the Toba eruption, the researchers report. The pollen analysis indicated a shift to a “more open vegetation cover and reduced representation of ferns, particularly in the first 5 to 7 centimeters above the Toba ash,” they wrote in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. The change in vegetation and the loss of ferns, which grow best in humid conditions, they wrote, “would suggest significantly drier conditions in this region for at least one thousand years after the Toba eruption.”

The dryness probably also indicates a drop in temperature, Ambrose said, “because when you turn down the temperature you also turn down the rainfall.”

The carbon isotope analysis showed that forests covered central India when the eruption occurred, but wooded to open grassland predominated for at least 1,000 years after the eruption.

“This is unambiguous evidence that Toba caused deforestation in the tropics for a long time,” Ambrose said.

This disaster may have forced the ancestors of modern humans to adopt new cooperative strategies for survival that eventually permitted them to replace Neandertals and other archaic human species, he said.

That last sentence regarding Neanderthal extinction seems to me to be stretching a point, especially when we bear in mind that Neanderthals survived Mount Toba by around 50,000 years, and there is nothing specific in the archaeological record that points to sudden innovations by AMH at this time. Even if we take into account the findings at Blombos for example, where it was originally proposed that the first modern human attempts at creating art were made, around 77,000 years bp, and subsequently at several even earlier sites in North Africa, it is clear that the path, or at least a side-road of that path to so-called modernity had been embarked upon prior to the eruption. It is notable howeverthat this particular mode of behaviour seems to disappear until modern humans made their mark in Upper Palaeolithic Europe around 42,000 bp.

To demonstrate that AMH would have changed the way in which they made a living to the extent that it gave them some sort of killer advantage would require a more exhaustive analysis on floral and faunal populations as well – obviously prey species would have been affected by the eruption, but whether entire species were wiped out causing AMH to adopt different food hunting and gathering methods is an open question. It seems parsimonious to suggest that a reduced human population would have been able to survive on a reduced (but not extinct) prey population, meaning that supply would still have roughly matched demand, and that no large changes in material culture would have been necessary.

What we don’t know of course is the impact the Toba eruption might have had on the mindsets of both AMH and Neanderthals who may have occupied the region,  and maybe late-surviving H. erectus, all of whom would no doubt have been awed by the sheer magnitude and extent of the destruction visited upon their world; titanic explosions that rained down debris from the sky, causing rapid deterioration of climate and associated habitats could well have spawned thoughts that the world was coming to an end, though whether such disasters were routinely ascribed to the natural world or some kind of divine or hellish intervention, is again, an unknown.

However, there is one location in Africa, and dated to 70,000 bp, that might offer an intriguing hint that some kind of behaviour linked to abstract belief through use of ritualistic symbolism in the guise of destruction, was present at this early date. The 2006 report, again from Science Daily, World’s Oldest Ritual Discovered Worshipped The Python 70,000 Years Ago documents a discovery by Associate Professor Sheila Coulson, from the University of Oslo, which describes what might be the earliest known example of the ritual destruction of humanly crafted objects, in this case, red spear-points, that were fashioned from stones sourced from hundreds of kilometres away from the Tsodilo Hills, site of the cave, described in part here:

“Stone age people took these colourful spearheads, brought them to the cave, and finished carving them there. Only the red spearheads were burned. It was a ritual destruction of artifacts. There was no sign of normal habitation. No ordinary tools were found at the site. Our find means that humans were more organised and had the capacity for abstract thinking at a much earlier point in history than we have previously assumed. All of the indications suggest that Tsodilo has been known to mankind for almost 100,000 years as a very special place in the pre-historic landscape.” says Sheila Coulson.

Sheila Coulson also noticed a secret chamber behind the python stone. Some areas of the entrance to this small chamber were worn smooth, indicating that many people had passed through it over the years.

Ostensibly there’s nothing to suggest that the human activities in this cave of the python were directly or even indirectly influenced by the Mount Toba eruption thousands of miles away, and indeed the dates for both the eruption and ritual activity in the African cave aren’t exact, but assuming Toba was the preceding event, it would be interesting to know if, when and to what extent news of Toba reached ancient African ears, and exactly how the eruption and ensuing catastrophic decline in environment and climate may have been reported and interpreted.

via Gene Expression

image: Landsat satellite photo of Lake Toba, Sumatra, Indonesia. (Credit: Image courtesy of NASA / via Wikimedia Commons)

References:

Environmental Impact of the 73 ka Toba super-eruption in South Asia, Article in Press, Corrected Proof , by Martin A.J. Williams , Stanley H. Ambrose, Sander van der Kaars, Carsten Ruehlemann, Umesh Chattopadhyaya, Jagannath Pal and Parth R. Chauhan, doi:10.1016/j.palaeo.2009.10.009

Middle Paleolithic Assemblages from the Indian Subcontinent Before and After the Toba Super-Eruption, by Michael Petraglia et al, Science 6 July 2007: Vol. 317. no. 5834, pp. 114 – 116 DOI: 10.1126/science.1141564

Current Anthropology, December 2009, Volume 50 number 6 is now out, which as will be apparent from the headline, marks no less than 50 years in the field, and there are a number of essays contained therein which reflect on the past, present and future of this publication. Here’s part of editor Mark Aldenderfer’s introduction to the proceedings:

In this issue we celebrate 50 years of Current Anthropology. By no means the most long‐lived anthropology journal (that honor must go to the Journal of the Royal Anthropological Institute, which technically began its run in 1872 but whose origins can be traced to 1863), it is certainly unique. The six celebratory essays explore the history of this remarkable journal from the perspectives of past editors, beginning with Cyril Belshaw, who took over from Sol Tax, the journal’s founder, and then Adam Kuper, Richard Fox, and Ben Orlove, as well as two past presidents of the Wenner‐Gren Foundation, Sydel Silverman and Richard Fox. Barbara Metzger, who joined the journal as a copy editor in 1964 at Tax’s behest and became arguably the central figure of the journal through the terms of five editors, provides another perspective on CA’s evolution. These very personal reflections offer us insights into not only the history of the journal but also the changing nature of scholarly publishing and the ways in which CA shaped, and was shaped by, the contours of these changes.

Although Sol Tax first saw CA as a venue for reviews and news, the realities of scholarly publishing even then moved him toward a broader conception of the idea of “current” research. Over the decades, as our editors have stressed, current meant just that—publishing not just the new for the sake of newness and currency but also the best of that research. Here the journal over the decades has been tremendously successful. Although I am aware of dissatisfaction with and rejection of quantitative measures of journal impact, such measures are nevertheless one way to document the quality of a journal and its influence on a field. Using the Institute for Scientific Information’s impact factor formula as reported in their annual Journal Citation Reports (see http://tinyurl.com/ygvxffq for definitions and caveats), since 1997, CA has ranged from the first to the seventh position of all indexed anthropology journals (lower numbers are better). This is a remarkable achievement for a four‐field journal in an era of increasing specialization, and the past editors must be heartily congratulated for keeping CA timely, relevant, and important to the field across these five decades. For the sake of modesty, I will forgo comparisons with the other two major four‐field journals!

As ever, the contents are behind a paywall, albeit one which in my opinion is very good value for money – as I’ve mentioned before, the cost of a digital annual subscription isn’t much different from what some journals charge for access to a single paper, and moreover the papers published in CA this year have been especially wide-ranging, informative and thought-provoking, a trend which I imagine will continue long into the future.

To access the Table of Contents, just click this link.

Back in August of this year, two words I frequently encountered when trying to visit sites of interest in Andalucía, southern Spain, were“Cerrado” (closed) and “No”, which as a tourist you take in your stride, leg it to the nearest hostelry and reconsider the rest of the day from the perspective of its slightly less interesting alternatives. As an eminent archaeologist working on what is potentially one of the more important sites in Spanish archaeology, with the prospect of confirming the latest known Neanderthals to have lived anywhere in the world, you might hope for more positive words from those tasked with permitting your work to go ahead unhindered. But as we see from the sorry tale unfolding below, this is not always the case, especially where the cave of La Carihuela is concerned.

Martin Cagliani at Mundo Neandertal points us towards this story, in which Spanish archaeologists are complaining that the local Junta (legislative assembly) of Andalucía will not allow the re-excavation of the Mousterian layers in the cave which it closed in 1996, (although work seems to have been conducted at least as late as 1998 by Carrión, linked PDF, Fig.2) where it is claimed there are Neanderthal remains dating to around 21,500 years bp, located within the cave of La Carihuela, about 45 km from Granada. If confirmed, this would make these Neanderthals far younger even than those whose artefactual traces have been found at Gorham’s Cave on Gibraltar dating to around 24,500 bp, at the same time perhaps taking the species’ existence right up to the Last Glacial Maximum.

The news article referred to is in Spanish, and is reported at Público.es, from which I’ll roughly translate some of the more pertinent points, while there’s also a freely accessible paper (PDF) on the subject of pollen sequences in the cave, as well as a description of its layout, the stratigraphic sequences within the galleries,  published in 2006, to which I’ll briefly refer throughout.

The report begins by describing how the cave might be the site of the very last Neanderthals tthat once walked this planet, because following the discovery of a male (Neanderthal) skull back in the 1950s, in the vicinity of Mousterian stone tools, it was realised shortly thereafter that according to pollen analyses, the layer from which the fossil had been retrieved might date to as late as 21,500 years bp.

Excavations began in earnest during the late 1970s, and by the early 1990s, a team of 30 researchers were working there, putting it on a par with Atapuerca, near Burgos in the north,  for the amount of effort invested in the site. But in 1996, following what is described as an arbitrary decision by local authorities, this work came to a sudden halt, and despite repeated requests from the archaeological community to reopen the cave, the Junta has remained obstinately silent on the case, allegedly not even picking up the phone to engage in the debate, according to D. Gerardo Vega Toscano. Profesor Titular, Dpto. de Prehistoria. UCM, Madrid.

He remarks that the scientists in this case are effectively at the mercy of the politicians, who basically don’t give two hoots whether the cave is the last refuge of the Neanderthals, or simply a hole in the ground.

One wonders from reading this whether the Junta is a fit and appropriate body to hold sway over such affairs, and moreover where the Spanish Ministry of Culture stands in this – surely it should be they who decide the scientific importance and appropriate funding levels required by such sites, and I find it hard to believe that no-one from the Ministry has seen fit to intervene.

Vega Toscano is for his part unconvinced of the very late date of 21,500 bp proposed for the remains, which he cites as absurd, opining instead that a date of 28,000 years bp is a more realistic proposition – it should be noted here that the estimate based on the pollen samples uses 28,440 bp and 21,430 bp as its parameters, with the real date presumably falling somewhere in between the two. The oldest known actual remains of Neanderthals are from Zafarraya, occupied between 31,000-27,000 bp, and the remains at La Carihuela should provide secure dates assuming that the specimens are in good enough condition.

Gorham’s Cave on Gibraltar is also known as a late Neanderthal refuge, with a most recent date of 24,500 bp ascribed there to Mousterian artefacts, while in Portugal at Lagar Velho, what appear to be the remains of a hybrid Neanderthal child are also put at 24,500 bp, so there seems no reason why a similar date shouldn’t apply at La Carihuela, and maybe 21,500 years bp, or a millennium or two beforehand, in the overall context isn’t completely out of the question. The fact that Mousterian technologies appear to have continued to be employed right up to the very end is interesting in itself, suggesting a lack of contact between archaic and anatomically modern populations – whether further investigations within Carihuela will reveal late-surviving Neanderthals were using bone or antler implements in addition to their own Mousterian tool-kits remains to be seen, but seems doubtful.

Contrary to the opinions of Vega Toscano, there is however support for the much later Neanderthal survival dates, as the article goes on to report the opinions of José Carrión, Professor of Botany at the University of Murcia, who remarks that 21,000 years bp marks the start of the Glacial Maximum, when temperatures plunged ever deeper for the following 3,000 years, a situation he believes could have tipped Neanderthals over the edge, coinciding with the extinction of fauna such as the mastodon and sabre-toothed tiger. (Although Neanderthals had previously survived through at least 2 previous ice ages, they had done so in the absence of competition from AMH, and as far as I’m aware, no major faunal extinctions had taken place in the earlier glaciations either, or at least not to the extent that Neanderthal prey animals disappeared from the menu).

Carrión further makes the point that apart from pollen dating, the bones from La Carihuela can be dated, and so might yet reveal themselves to be younger than the Gorham’s Cave presence – whether the fossil skull mentioned earlier has been dated isn’t stated here, and whether it continues to languish unexamined in a Granada museum, isn’t clear. Other researchers have dismissed the idea that climate alone could have accounted for the demise of the Neanderthals, preferring instead to cite a multitude of inter-related factors.

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As this paper is freely accessible for the next 7 days, I’m posting it here in the hope that as many readers as possible will have time to read it through. Molly Fox et al turn their thoughts to the question of why women are able to live for many years after they able to conceive offspring, a phenomenon seemingly at odds with the idea that members of a species tend to die off once their reproductive days are over.

The ‘Grandmother Hypothesis’ is described and expanded upon thus in the linked paper:

With menopause occurring around age 50, women survive several decades longer than their gametes (Dorland et al. 1998; Hawkes 2003). Why should women have such conservative life histories that they save up enough energy for 25 years of reproductive retirement? Human females represent a particular conundrum in evolutionary studies: after menopause they are unable to reproduce and have no obvious way to increase their genetic contribution to future generations. As this is the basis for natural selection, many researchers have sought to explain how post-menopausal longevity is adaptive in women.

Among evolutionary biologists, the ‘grandmother hypothesis’ is the most widely recognized explanation for human female post-reproductive longevity. It suggests that vigorous, skilled, elderly women are able to contribute to their grandchildren’s survivorship through nutritional provisioning (Hawkes et al. 1998; Hawkes 2003). According to Hamilton’s relatedness coefficients (Hamilton 1966), grandmothers share a quarter of their DNA with grandchildren, and so a woman can increase her genetic contribution to subsequent generations by keeping her grandchildren alive and healthy. Supporters of this model often refer to the Hadza, a modern foraging society in Tanzania, where grandmothers are more effective than children at extracting tubers from the dry ground. While a mother is breastfeeding an infant, and thus unable to forage enough to provide for weaned children, the grandmother provides food for the older siblings (Hawkes 2003; Hawkes & Jones 2005).

The authors further suggest that this may be a behavioural and survival trait that can trace its roots back to the early Pleistocene, 1.7m-1.9m years bp (described in the paper as the Plio-Pleistocence boundary, recently re-dated to 2.6m years bp), when global cooling caused the expansion of African tuber-friendly grasslands, prompting ancient hominids to include a great many more tubers in their diet. From these origins, where grandmothers are suggested to have been important contributors of nutrition to two generations of descendants, researchers such as Soffer and Adovasio have taken the theory further, suggesting that grandmothers contributed a much greater role in child-rearing than simply providing nutritional foodstuffs.

The interesting aspect of this paper is how the authors suggest simply having a grandmother isn’t equally beneficial to grandchildren of either gender, with clear differences suggesting that in some instances having a maternal grandmother can be better for boys than a paternal grandmother, whilst a grand-daughter with a maternal grandmother appears to benefit most of all, as indicated here:

Tests of the grandmother hypothesis have been carried out on modern and historical populations. Most of the data correlate grandchild survivorship with grandmother survival and/or proximity, and it is often reported that only maternal grandmothers (MGMs) are found to have a positive effect on grandchild survivorship (Sear et al. 2002; Voland & Beise 2002). Studies that have not distinguished between MGMs and paternal grandmothers (PGMs) have found no correlation between grandmother’s presence and grandchild survivorship (Hill & Hurtado 1991; Lahdenperä et al. 2004). To date, only two previous studies known to the authors have distinguished between boys and girls when investigating the effect of both grandmothers.

A study of a Japanese population found that the presence of a PGM had a negative effect on boys and a positive effect on girls, while the presence of an MGM had a positive effect on children of both sexes, especially on boys (Jamison et al. 2002). They point to cultural features of the society as a possible mechanism for these findings. A study of an Ethiopian population reported the sex-specific information, but it was not analysed in the paper (Gibson & Mace 2005). More tests of the grandmother hypothesis are summarized in Sear & Mace (2007).

The authors continue by proposing the following:

The grandmother hypothesis is based on the fact that women are genetically related to their grandchildren, and we should not overlook the nature of that genetic relatedness. Grandsons and granddaughters differ in the proportion of their X-chromosomes shared with MGMs and PGMs (figure 1). According to our proposed X-linked grandmother hypothesis, if grandmothers invest in grandchildren because of their genetic relatedness with them, then their adaptive incentive to invest may vary in a way that mirrors this variation in genetic relatedness. As a consequence, grandmothers’ differential investment in grandchildren could cause differential survivorship of those grandchildren…

…Although the X-chromosome contains only about 4.4 per cent of our DNA, with its estimated 1529 genes, it contains perhaps approximately 8 per cent of all human genes (Pennisi 2003; NIH 2007; Parang et al. 2008; NCBI 2009a). The dramatic differences in X-relatedness between grandmothers and grandchildren confound the Hamiltonian concept that grandchildren are 25 per cent genetically related to each grandparent. If approximately 92 per cent of our genes are autosomes, then a grandmother shares one-quarter of that, or approximately 23 per cent of her total genes with a grandchild, plus X-relatedness.¹

If a grandmother shares no X-chromosome with a grandchild, then their overall genetic relatedness is approximately 23 per cent, and if they share an entire X-chromosome, then it would be approximately 31 per cent. Therefore, MGMs and grandchildren are likely to share 25 per cent of their genomes, while PGM and granddaughter may share a total of approximately 31 per cent of their genes, with a likelihood of 27 per cent inheritance, while a PGM and grandson may share only approximately 23 per cent.

We can only wonder whether these conclusions were borne out in ancient communities and whether it was realised that there was closer bonding and greater survival amongst children with certain alloparental configurations, or whether child-care was undertaken on a more ad hoc basis, whereby other surrogate mothers who were still of reproductive age were also co-opted into rearing off-spring when the need arose. Moreover, infant mortality was probably high and seemingly arbitrary, especially where actions of predators, illness and infections were concerned, in which case the grandmother effect would have been diminished, except in those cases where an older person such as a grandmother would have had greater experience in recognising symptoms and knowing of potential remedies, something which presumably could also have applied also to grandfathers.

I’m not sure at what age humans living in the early and later stages of the Pleistocene would have become grandparents, but my guess would be quite young, possibly by age 30-35, though whether females would also have become unable to conceive by that age I don’t know; but it seems there could have been some overlap, during which time a grandmother could herself have still given birth to children, unless a menopausal clock kicked in soon after their own off-spring had given birth, which seems unlikely. If we still assume an age of 50 for menopause however, by the time she reached 50, a Pleistocene woman could easily find herself in the role of great-grandmother, though whether humans in significant numbers reached that ripe old age back then, again seems unlikely.

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There’s been some coverage of a recent announcement by Svante Pääbo of the Max Planck Institute, who opines that Neanderthals and anatomically modern humans had sexual encounters as they co-habited in Upper Palaeolithic Eurasia from around 42,000 bp to 24,500 bp. The main article is over at the London Times, from which this is an excerpt:

Paabo recently told a conference at the Cold Spring Harbor Laboratory near New York that he was now sure the two species had had sex — but a question remained about how “productive” it had been.  “What I’m really interested in is, did we have children back then and did those children contribute to our variation today?” he said.

“I’m sure that they had sex, but did it give offspring that contributed to us? We will be able to answer quite rigorously with the new [Neanderthal genome] sequence.”  Such an answer might ease the controversy over recent contradictory discoveries regarding Neanderthals. Some fossils seem to have both modern human and Neanderthal features, suggesting that the two species interbred. Yet DNA scans have shown that Neanderthal genes were very different from those of modern man.

Pääbo is reported to be at the point of publishing his analysis of the Neanderthal genome, and it seems clear that he has gleaned something from the data that has prompted this latest assertion; previous research has been interpreted as indicating that if the two species did interbreed it was at a very low level, apparently evidenced by the almost complete lack of a Neanderthal presence in our own genome today.

Gene Expression comments thus:

The way Paabo is couching it, what he has found then seems likely to be evidence that humans who had just expanded Out of Africa contributed to the genomes of Neandertals. In other words, modern human introgression into Neandertals. Of course if the gene flow was from modern human to Neandertals exclusively, then it would be an evolutionary dead end since that lineage went extinct.

In any case, for several decades some fossil-based paleoanthropologists have been claiming that there are “intermediate” individuals in the record which indicate modern human-Neandertal hybridization. Most prominently Erik Trinkaus. If Paabo’s finding becomes more solid, then it seems time to update the probabilities on these sorts of claims based purely on morphology.

The story is taken up at Ad Hominin, where the following opinion is expressed:

Today, most researchers acknowledge that some sexual encounters could have occurred between Neandertals and modern humans. The more interesting question is how common were these encounters and did they leave their mark on the modern gene pool. Undoubtedly, modern humans and Neandertals would have recognised each other as fellow humans but this does not mean that they would have acted humanely to each another.

Countless social and psychological studies have shown humans to have a very strong “us versus them” mentality, that no doubt also existed in our ancestors. It is unlikely that modern humans and Neandertals had an easy relationship. Most sexual encounters that took place between the two were likely opportunistic and probably involved enslavement and rape.

Of course we have absolutely no evidence regarding the circumstances under which these liaisons may have taken place, and I imagine the last sentence of the quote above is obliquely referring to the way in which the indigenous Indian populations of the Americas were almost wiped from the face of the Earth by the tide of white Europeans, who staged one of the most brutal and violent land-grabs in recorded history, as they claimed other peoples’ territories for their own, killing thousands in the process.

However, Upper Palaeolithic Europe was a very different place to the Americas of a few centuries ago, with no centralised governments, mobilised armies, or even slavery, as suggested above. I’m not even sure what the duties of a putative slave in the UP would actually be, or how such a state of affairs could even be enforced. The sheer numbers of humans involved in the theft of native peoples’ lands far eclipsed the populations of Ice Age Europe, so although there might have been competition for land and resources, it would have been on a far smaller scale than in modern times.

Moreover, the technological and cultural gap between Neanderthals and incoming moderns was comparatively narrow, as opined by Professor Chris Stringer of the Natural History Museum in London:

“It’s possible that Neanderthals and humans were genetically incompatible, so they could have interbred but their children would have been less fertile,” said Stringer.  This phenomenon is seen in many other species such as when lions breed with tigers and horses breed with zebras.  “I used to believe Neanderthals were primitive,” said Stringer, “but in the last 10,000-15,000 years before they died out, around 30,000 years ago, Neanderthals were giving their dead complex burials and making tools and jewellery, such as pierced beads, like modern humans.”

The popular notion of inter-species sex, as apparent in the previously quoted post, was that brutish Neanderthal men had their wicked way with anatomically modern women by dragging them behind the nearest bush, reinforcing the old stereotype of rapacious cavemen that has so blighted the way in which our archaic ancestors have been viewed for nigh on 150 years.

Because the population of Europe in the Upper Palaeolithic was probably very low in both modern and archaic communities, contact was likely to have been infrequent – indeed it seems quite possible that members of both species lived entire lifetimes without encountering one another – as Neanderthal numbers began to decline, any encounters would become increasingly rare.

And when moderns and Neanderthals did make primary contact, it could have been under any number of circumstances, some of which may have resulted in violence and death, whilst others might have developed into co-operation, friendship, up to and including, romance and kisses. Yet other encounters might have ended in polite ‘nice-to-meet-you’ handshakes, after which the two species quietly got on with minding their own business, without harbouring any particular feelings for or against their new acquaintances.

As a brief aside, I can’t help but speculate that it might have been easier for Neanderthal women to give birth to inter-species offspring than their AMH counterparts – bearing in mind that Neanderthal babies were more robust, the shape and size of their skulls, even when hybridised, would have made it more difficult for AMH mothers to give birth. A Neanderthal woman who had conceived a child fathered by an AMH male would maybe have found it easier to give birth to the hybridised and possibly smaller baby she was carrying – so should we expect to find that hybridised children conceived by Neanderthal women survived in greater numbers than those conceived by AMH mothers? And how would we then consider the evolutionary social factors that led to relationships between the two species that caused AMH men to bond and breed with Neanderthal women? Such a question may be answered in part from this further quote from Ad Hominin:

The recent announcement by Svante Pääbo that he is sure that Neandertals and modern humans had sex is quite a bold pronouncement coming from a scientist. It raises the question of whether this ascertain is based on some hard evidence they found while sequencing the Neandertal genome. It is possible that if there was some Neandertal genes passed on to the first moderns in Europe, they could have got eliminated from the subsequent gene pool as population sizes fluctuated during the more severe climatic episodes. A more likely scenario is that Pääbo’s team found evidence of modern introgression in the Neandertal genome. In all likelihood the incoming modern humans were more numerous than the Neandertals, thereby absorbing the endemic populations through genetic swamping.

This would seem to reinforce the point that any enforced sex is more likely to have been instigated by incoming AMH males on the female Neanderthal population, if we are to take modern history of human conquest and genocide into account and apply the same mind-set to life 30,000 to 40,000 years ago. But the fact that the both modern and archaic populations may have co-existed in Europe for 10,000-15,000 years at least hints that there was no large-scale or organised species cleansing undertaken by AMH, and it’s quite possible that both they and the Neanderthals behaved a great deal better towards each other than has often been the case in our own recorded histories.

It remains to be seen whether this latest research is able to resolve this question of interbreeding, or whether instead tentative clues will emerge that raise more questions than answers.

See also: Video – Svante Pääbo discussing the Neanderthal Genome Project on YouTube.

Science Daily report on a paper published back in June which I appear to have missed, and as it’s freely accessible at PNAS, I’m pleased to be able to link to it here. This is the abstract:

Food storage is a vital component in the economic and social package that comprises the Neolithic, contributing to plant domestication, increasingly sedentary lifestyles, and new social organizations. Recent excavations at Dhra’ near the Dead Sea in Jordan provide strong evidence for sophisticated, purpose-built granaries in a predomestication context
11,300–11,175 cal B.P., which support recent arguments for the deliberate cultivation of wild cereals at this time. Designed with suspended floors for air circulation and protection from rodents, they are located between residential structures that contain plant-processing instillations. The granaries represent a critical evolutionary shift in the relationship between people and plant foods, which precedes the emergence of domestication and large-scale sedentary communities by at least 1,000 years.

One of the authors is Ian Kuijt, who in the current edition of Current Anthropology authored a paper addressing the same subject, namely ‘What Do We Really Know about Food Storage, Surplus, and Feasting in Preagricultural Communities?’ which is behind a subscription paywall, so here’s a brief extract from that:

Food production, social inequality, and storage are interrelated. Despite the general acceptance of this proposition, the roles of storage in emerging social inequality and the development of food production remain poorly understood. Food storage is an awkward topic for researchers as it is not always manifested in ways that are visible or material (see Forbes and Foxhall 1995; Ingold 1983; Stopp 2002; Testart 1982). The reconstruction and definition of what is storage is highly complex, and centers on practices and materials that are not always well preserved.

The identification of storage features, as well as the scale of storage, is undermined by several constraints. First, due to differential preservation, not all food storage can be identified in the archaeological record. While not random, direct preservation of foods through burning or other agents of conservation is inconsistent and unlikely to be representative of the entire range of foods used and stored in a prehistoric economy.

Second, ethnographic accounts of hunter‐gatherers and farmers provide evidence for a wide range of storage practices, some of which occur off site (Stopp 2002). Third, while we can use ethnography to help us understand the past use of architectural features, it is possible that Neolithic storage practices differed from our comparative cases. The archaeological understanding of past storage practices is based largely on preserved features and structures that are empty, and burned paleobotantical remains are rarely recovered. Researchers are often left with no alternative but to develop circumstantial arguments that specific features were used for food storage.

Some researchers (e.g., Hayden 2009, in this issue) argue that the pre‐agricultural Near Eastern Early (14,500–12,800 cal BP) and Late Natufian periods (12,800–11,500 cal BP) were characterized by sufficient food storage and surplus to allow for individuals to gain social power over others. The Natufian periods, which are distinctly different from each other, were characterized by significant seasonal residential sedentism and the extensive harvesting of wild plants (Bar‐Yosef 1998). As with earlier peoples, the Early and Late Natufians were focused on intensive and extensive harvesting of wild cereals (Bar‐Yosef 1998). Natufian people utilized a remarkably wide range of wild plants and animals and probably had a detailed knowledge of the seasonality and availability of these resources. Certainly the increased degree of sedentism in the Early Natufian period suggests that people were able to reduce seasonal food risks to the point where they could live in the same areas for one or more season of the year.

References: Evidence for food storage and predomestication granaries 11,000 years ago in the Jordan Valley, by Ian Kuijt and Bill Finlayson, Published online before print June 22, 2009, doi: 10.1073/pnas.0812764106

Rethinking the Origins of Agriculture: What Do We Really Know about Food Storage, Surplus, and Feasting in Preagricultural Communities? by Ian Kuijt, Current Anthropology Volume 50, Number 5, October 2009 © 2009 by The Wenner‐Gren Foundation for Anthropological Research. All rights reserved. 0011-3204/2009/5005-0009$10.00 DOI: 10.1086/605082