A note on the use of temporal frequency distributions in studies of prehistoric demography

Temporal frequency distributions of archaeological sites and radiocarbon dates are commonly used as proxies for prehistoric population levels based on the assumption that more people create a stronger archaeological signal. While this assumption is certainly correct, we question whether relative frequencies of sites or dates observed from prehistoric contexts are necessarily linked to human demography. In this paper, we demonstrate that the typical positive curvilinear frequency distributions observed in archaeological contexts also regularly occur in paleontological and geological contexts and are thus likely caused by the operation of time-dependent destructive processes, what we call “taphonomic bias.” Using a simple model, which assumes a constant rate of site loss over time, we show how taphonomic bias can produce positive curvilinear frequency distributions through time even in cases of population stasis, decline, and fluctuation. We conclude that caution must be used when attempting to infer demographic trends from frequency distributions alone.     

Deglaciation and Colonization: Pioneer Settlements in Northern Fennoscandia

We present new data on Early Mesolithic settlements in northern Sweden and discuss the process of pioneer colonization. A new set of radiocarbon dates from archaeological sites push deglaciation of northern Fennoscandia further back in time and demonstrate the rapid arrival of pioneer settlers. Environmental data reveal a highly productive early postglacial setting with plant communities unmatched in present ecosystems. The chronological and technological setting supports immigration from the north and northwest with pioneers relying on a long history of enculturating northern subarctic landscapes.     

Radiocarbon calibration curves,summed probability distributions,and early Paleoindian population trends in North America

Archaeologists increasingly examine summed probability distributions of radiocarbon dates to search for temporal trends in ancient human populations, including early North American population trends across the onset of the Younger Dryas climatic period (10,900 BC). We use both IntCal04 and IntCal09 to simulate and calibrate sequences of radiocarbon dates that represent evenly spaced calendar ages from 12,000 to 9000 BC and use IntCal09 to simulate two different demographic processes across this interval. The shapes of the calibrated summed probability distribution from our first set of simulations mirror many trends that have been interpreted in demographic terms and this shape shows clear links to the shape of the radiocarbon calibration curve. This is true for both IntCal04 and IntCal09, although these different curves produce different probability distributions. The shapes of the calibrated summed probability distribution from our second set of simulations differ somewhat but show virtually identical trends at points where the actual frequencies of calendar dates are very different. We conclude that changing frequencies of radiocarbon dates over time probably do contain demographic information, but that extracting this information is more difficult than archaeologists have acknowledged.     

Temporal frequency distributions of alluvium in the American Southwest: taphonomic,paleohydraulic, and demographic implications

The use of radiocarbon frequency distributions to reconstruct prehistoric human and animal populations must account for taphonomic loss and other factors that affect the archaeological and paleontological records. Surovell et al. (JAS, 36, 1715–1724) have recently proposed a correction for “taphonomic bias” that is based on the radiocarbon frequency of a global sample of volcanic deposits. Analysis of 717 radiocarbon dates sampled from the alluvium of the San Pedro and Santa Cruz rivers and their tributaries in southeastern Arizona shows that discovery and scientific biases also play an important role in the creation of radiocarbon frequency distributions, and that the rate of “taphonomic bias” in prehistory is not predicted by the radiocarbon frequency of volcanic deposits. The latter principle is further argued using a sample of 123 Pliocene to Clovis-age proboscideans from the San Pedro Valley. We propose an alternative model that is based on the nature of the stratigraphic record, with discovery bias, scientific bias, taphonomic loss, and the shape of the calibration curve all operating to influence the temporal frequency distribution of radiocarbon-dated prehistoric phenomena.     

Prehistoric population history: from the Late Glacial to the Late Neolithic in Central and Northern Europe

Summed probability distributions of radiocarbon dates are used to make inferences about the history of population fluctuations from the Mesolithic to the late Neolithic for three countries in central and northern Europe: Germany, Poland and Denmark. Two different methods of summing the dates produce very similar overall patterns. The validity of the aggregate patterns is supported by a number of regional studies based on other lines of evidence. The dramatic rise in population associated with the arrival of farming in these areas that is visible in the date distributions is not surprising. Much more unexpected are the fluctuations during the course of the Neolithic, and especially the indications of a drop in population at the end of the LBK early Neolithic that lasted for nearly a millennium. Possible reasons for the pattern are discussed.     

Prehistoric demography of North America inferred from radiocarbon data

Large radiocarbon datasets are increasingly used as a paleodemographic proxy, although potential sources of bias in such records are poorly understood. In this paper, we use more than 25,000 radiocarbon dates extracted from the Canadian Archaeological Radiocarbon Database (CARD) to estimate long-term population trends in North America, while critically examining biases in such records. The frequency distribution of CARD dates shows a positive curvilinear pattern, such that older dates exist in lower numbers than more recent dates, which in part reflects the removal of cultural carbon from the archaeological record through processes such as erosion and dissolution. The average annual growth rate of radiocarbon dates in CARD was calculated and used to derive estimates of the population of North America from the Paleo-Indian to the Contact Periods. While taphonomic bias has likely affected the CARD data, other factors, such as the overrepresentation of Paleo-Indian and Archaic radiocarbon dates, may have offset any bias due to taphonomy. A quantitative reconstruction of Native American population shows that population increased rapidly around 2000 cal yr BP, reaching a maximum of 2,500,000 people by ～AD 1150. From this time until European contact, the population declined, possibly due to the effects of increased sedentism and population density.     

Ancient DNA reveals a major genetic change during the transition from hunting economy to reindeer husbandry in northern Scandinavia

The timing and origin of reindeer domestication has been highly debated. Recent molecular analyses show several mitochondrial lineages of domestic reindeer across Eurasia suggesting different origins of Fennoscandian and Siberian domestic reindeer. In order to investigate the origin of domestic Fennoscandian reindeer, we sequenced a mitochondrial control region fragment of 68 ancient reindeer remains from archaeological sites in Finnmark, the major county for extant reindeer husbandry in Norway, spanning from ca. BC 3400 to AD 1800. The majority of the Stone and Iron Age reindeer assemblages in Finnmark are from settlements in the eastern part of the county, in the Varangerfjord area. The reindeer remains from these settlements show affiliation to the large and complex Beringian haplotype cluster, found in extant reindeer from the Kola Peninsula to north-eastern Russia. A distinct haplotype shift is observed in the late medieval period, when the typical haplotype signatures of extant domestic Fennoscandian reindeer appeared in coastal regions of both eastern and western Finnmark. These haplotypes were not found among the Stone and Iron Age wild reindeer samples of Finnmark, suggesting that this population was not ancestral to extant domestic reindeer of Fennoscandia.     

Correcting temporal frequency distributions for taphonomic bias

In this paper, we expand upon a prior study [Surovell, T.A., Brantingham, P.J., 2007. A note on the use of temporal frequency distributions in studies of prehistoric demography. Journal of Archaeological Science 34, 1868–1877.] that explored the problem of taphonomic bias. Taphonomic bias refers to the tendency for younger things to be over-represented relative to older things in the archaeological record due to the operation of destructive processes like erosion and weathering. Using a database of radiocarbon dated volcanic deposits from Bryson, R.U., Bryson, R.A., Ruter, A. [2006. A calibrated radiocarbon database of late Quaternary volcanic eruptions. Earth Discussions 1, 123–124.], we develop an empirical model of taphonomic bias. In contrast to our prior study in which we modeled taphonomic bias as an exponential function wherein the likelihood of site loss remains constant through time, we argue that the probability of site destruction actually decreases with site age. We further demonstrate how this model can be used to correct temporal frequency distributions and extract demographic histories. We illustrate this approach using databases of radiocarbon dates from rockshelter and open-air sites in the Bighorn Basin, Wyoming, USA, and mammoths and humans in Siberia, Russia.     

Spatial dynamics of human dispersals: Constraints on modelling and archaeological validation

In recent years there has been growing interest in the application of travelling wave models to the spatial dynamics of human dispersals, and their archaeological validation. These models enable predictions of the velocity of population expansion, derived from estimates of reproductive rates and of individual mobility. In this paper we discuss some intrinsic constraints on the application of such models to dispersal events which have been documented in the archaeological record. There is significant uncertainty in radiocarbon dating of first occupation at different locations, and in the reconstruction of evolving population distributions from time-averaged archaeological distribution maps. We calculate some archaeological boundary conditions for the accurate estimation of travelling wave profiles and velocities, and demonstrate their significance for two archaeological case studies: the first peopling of the Americas, and the Neolithic transition in Europe.     

RADIOCARBON DATING ARCHAEOLOGICAL SAMPLES IN THE EASTERN MEDITERRANEAN, 1730 TO 1480 BC: FURTHER EXPLORING THE ATMOSPHERIC RADIOCARBON CALIBRATION RECORD AND THE ARCHAEOLOGICAL IMPLICATIONS*

The East Mediterranean Radiocarbon (Inter‐)Comparison Project (EMRCP) has measured time series of radiocarbon ages for known age samples of German oak (GeO) and for samples from the near‐absolutely placed Gordion juniper dendrochronology from central Anatolia. In this paper, we review the data for the calendar years from 1730 to 1480 bc , relevant in particular to controversy and debate concerning the absolute date of the Minoan eruption of the Santorini (Thera) volcano. We consider the issue of the radiocarbon (¹⁴C) dating of the Santorini eruption, and the problem of how this relates to the archaeological record and historical chronology of Egypt in light of the ¹⁴C data. We find that these ¹⁴C data, and other recent radiocarbon work, provide good grounds to be confident in the possibility of a robust radiocarbon‐based chronology for the eastern Mediterranean. In contrast, as the radiocarbon case becomes stronger, questions must be asked about some archaeological dating: in particular, at the site of Tell el‐Dab‘a in the Nile Delta of Egypt.     

Invited response to K. Ryan’s comments on Coltrain et al. (2004) and Coltrain (2009): is Native Point “Burial 21” Dorset in age; were historic-era burials European in origin and how important were caribou in Sadlermiut diets?

This is an invited to response to K. Ryan’s comments on Coltrain et al. (2004) and Coltrain (2009). Both publications present stable isotope data and AMS radiocarbon dates on a suite of eastern Arctic burials from three sites in north-western Hudson Bay. In these articles, we examined the importance of bowhead whaling among Thule foragers at Silimiut and Kamarvik and contrasted their subsistence strategies with those of the proto-historic Sadlermiut, using the stable and radio-isotope chemistry of purified bone collagen to monitor variability in resource acquisition over time. Ryan dismisses a Dorset-era radiocarbon date on a burial collected by Collins from the T-1 site asserting that a single radiocarbon measurement is not a reliable indicator of age and thus the burial is Sadlermiut not Dorset. She also contests our assessment that two historic-era individuals in the Sadlermiut mortuary assemblage were either European or consumed diets relatively high in European foods. Ryan further argues that our reconstruction of protohistoric Sadlermiut diets is not in keeping with the archaeofaunal record. Her primary concern is a perceived lack of agreement between a subset of our findings and the archaeological record.     

A comment on Steele’s (2010) “radiocarbon dates as data: quantitative strategies for estimating colonization front speeds and event densities”

We show that Steele’s (2010) criticisms of Hamilton and Buchanan (2007) and Buchanan et al. (2008) do not hold water and demonstrate that his re-analyses of Hamilton and Buchanan’s (2007) and Buchanan et al'.s (2008) datasets are flawed. In the process, we highlight some important issues for researchers interested in using radiocarbon dates to reconstruct population movements and demography. Most notably, we explain why OLS regression is preferable to RMA regression when estimating diffusion velocity, and demonstrate that the summed probability distributions yielded by CalPal are more reliable as guides to past demographic change than those produced by Calib and OxCal.     

The earliest evidence of domesticated wheat in the Crimea at Chalcolithic Ardych-Burun

Abstract

This paper reports the discovery of the earliest evidence of domesticated wheat in the Crimean peninsula from the Ardych-Burun shell midden site, Ukraine. The Ardych-Burun site dates to middle of the 4th millennium cal b.c. For the first time, the chronology of a Ukrainian Chalcolithic period site has been established through direct radiocarbon dating of cereal grains retrieved from it. This discovery allows for a wider discussion of the chronology and geographical origins of domesticated plant species in Ukraine and the role the Caucasian corridor may have played in the spread of agriculture into eastern Europe. The presence of cereal crops in the southern Crimea enriches our understanding of the subsistence strategies of the coastal population, which was previously linked only with pastoralism, hunting, and the exploitation of marine resources.     

Reevaluating the Age of the Iberomaurusian in Morocco

Chronological evidence for the Iberomaurusian is currently very limited and there are problems with some of the published radiocarbon dates. In this paper we present new AMS dating results from well-stratified cave sequences at Ghar Cahal, Kehf el Hammar and Taforalt in northern and eastern Morocco. The longest of these sequences, from Taforalt, shows an intermittent occupation history spanning the period ca. 18,000–11,000 bp (radiocarbon determinations presented in this paper are expressed as ka bp or bp, whilst approximate calendar ages are expressed as Cal bp) with a marked intensification of cave use soon after ca. 13,000 bp. Using calibrated AMS ages in comparison to sea surface temperature evidence from the Alboran Sea core MD95-2043 and more generally to Greenland ice δ¹⁸O core records, we suggest that there may have been a relationship, albeit a complex one, between climatic events and cave activity on the part of Iberomaurusian populations.     

The use of summed radiocarbon probability distributions in archaeology: a review of methods

Using a database of Australian archaeological radiocarbon dates (n = 2996), this paper explores three key methodological issues associated with the use of summed probability plots of radiocarbon data: 1) the minimum sample size needed for a statistically reliable plot; 2) the effect of radiocarbon calibration on the structure of these plots; and 3) the application of a taphonomic correction to such time-series data. The results identify several protocols, recommended as best-practice when using summed probability plots: 1) a minimum sample size of 500 radiocarbon dates should be used, and the sample size and the mean of the standard deviations of the radiocarbon dates (ΔT) in the sample should both be reported; 2) a moving average trendline of 500-800 years should be used to offset the effects of the calibration process; and 3) Surovell et al. “Correcting temporal frequency distributions for taphonomic bias” [Journal of Archaeological Science 36 (2009) 1715-1724] is explored, with modifications and temporal limits (<25,000 cal years BP) proposed. Correction of time-series data using theoretical taphonomic correction curves is useful as a heuristic tool but can obscure real trends if applied routinely. Comparison between summed probability plots and other occupation data is presented and shows good correlation. However it is recommended that plots are supplemented by other archaeological indices and the cross-comparison of such multiple proxies will strengthen identification of occupation trends.     

A northern Neolithic? Clay work,cultivation and cultural transformations in the boreal zone of north‐eastern Europe,c.5300–3000 bc

The adoption of pottery in eastern Fennoscandia in the later sixth millennium BC has traditionally been understood in straightforward technological and practical terms, and as a development that did not mark other significant changes in local culture or ways of life. Recent research in the region, combined with new ideas about Neolithization in Eurasia more generally, nonetheless suggests that the adoption of pottery was associated with more fundamental cultural and environmental transformations than has previously been thought. This article brings together diverse old and new data from north‐eastern Europe and discusses the character and dynamics of cultural and human‐induced environmental change following the adoption of pottery. The aim is to provide a scenario of long‐term cultural changes and, in particular, to consider the significance and broader implications of the very practices of clay use and cultivation, as well as their links to wider cultural and environmental phenomena.     

Optically stimulated luminescence dating of Southern High Plains archaeological sites

The Southern High Plains of North America is rich in archaeological sites, but many are not well constrained chronologically, owing to a lack of material for radiocarbon dating. A program of optically stimulated luminescence (OSL) dating, applying mainly single-grain analyses, was therefore initiated. Many samples have independent age estimates from radiocarbon to check the OSL results, but OSL age estimates are also provided for those sites that otherwise lack secure chronological control. Sediment samples for OSL were obtained primarily from Paleoindian and Archaic localities, though include deposits of more recent age. Through the analysis of single grains, equivalent dose—the numerator of the age equation—is evaluated independently on numerous grains. The distribution of these values is relatively broad for some samples, and this is attributed to post-depositional mixing. Mixing is also evident in some samples with more narrow distributions. Selecting portions of the mixed distributions for age determination allows more accurate dating for some samples, but the nature of the distributions limits the resolution on others, conclusions that cannot be as easily drawn from multi-grain analysis. Where independent age control is available, most OSL results broadly conform; however, some samples show discrepancies that are not readily explained, but may relate to association or dose rate problems. This underscores the desirability of obtaining where possible suites of chronological evidence.     

Towards a Chronology of the Jerzmanowician—a New Series of Radiocarbon Dates from Nietoperzowa Cave (Poland)

The period around 50 000–35 000 years ago constitutes one of the most debated research issues in European archaeology of the Palaeolithic. In this time period, the transition from the Middle to the Upper Palaeolithic took place. Locally, in different areas of Europe, this shift is recorded in so‐called transitional assemblages. The eastern fringe of these transitional assemblages is represented by the Jerzmanowician, the unit described on the basis of a lithic assemblage from Nietoperzowa Cave (Poland). The unit is a part of a European transitional complex called the Lincombian–Ranisian–Jerzmanowician. Up to now, the radiocarbon dates presented in the literature have only allowed us to set the age of the Jerzmanowician at c.40 000–45 000 ka cal bp . In this study, we present 42 new radiocarbon dates. We attempt to set the archaeological record of the Jerzmanowician from Nietoperzowa Cave in an accurate chronological framework, based on Bayesian statistical processing of radiocarbon dates. We conclude that the lower boundary of layer 6 in Nietoperzowa Cave can be statistically located in the range 44 000–42 000 cal bp and the upper limit for the Jerzmanowician is estimated to c.31 000 cal bp . New data raises a question on the correlation with upper layer 4. In the light of the new chronology, the attribution of the archaeological inventory from layer 4 to the Jerzmanowician seems questionable.     

Population and forest dynamics during the Central European Eneolithic (4500–2000 BC)

The population boom-and-bust during the European Neolithic (7000–2000 BC) has been the subject of lively discussion for the past decade. Most of the research on this topic was carried out with help of summed radiocarbon probability distributions. We aim to reconstruct population dynamics within the catchment of a medium sized lake on the basis of information on the presence of all known past human activities. We calculated a human activity model based on Monte Carlo simulations. The model showed the lowest level of human activity between 4000 and 3000 BC. For a better understanding of long-term socio-environmental dynamics, we also used the results of a pollen-based quantitative vegetation model, as well as a local macrophysical climate model. The beginning of the decline of archaeologically visible human activities corresponds with climatic changes and an increase in secondary forest taxa probably indicating more extensive land use. In addition, social and technological innovations are important, such as the introduction of the ard, wheel, animal traction and metallurgy, as well as changes in social hierarchy characterizing the same period.