Elsevier

Quaternary International

Volume 242, Issue 2, 15 October 2011, Pages 570-583
Quaternary International

Multiple lines of evidence for possible Human population decline/settlement reorganization during the early Younger Dryas

https://doi.org/10.1016/j.quaint.2011.04.020Get rights and content

Abstract

Three approaches are used to test whether or not human populations across North America were affected by abrupt climate change and/or other environmental factors associated with the onset of the Younger Dryas (YD) cooling episode at ca. 12,900 cal BP. They are: (1) frequency analyses of Paleoindian projectile points from across North America; (2) time series of lithic assemblages from eleven Paleoindian quarry sites in the southeastern United States; and (3) summed probability analyses (SPA) of radiocarbon dates from cultural (human-related) sites across North America and parts of the Old World. The results of each analysis suggest a significant decline and/or reorganization in human population during the early centuries of the YD, varying in extent by region. Archaeological settings formerly heavily utilized, such as stone quarries in the southeastern U.S., appear to have been largely abandoned, while over large areas, a substantial decline occurred in the numbers of diagnostic projectile points and cultural radiocarbon dates. Later in the YD, beginning after about 12,600 cal BP, there was an apparent resurgence in population and/or settlements in many areas, as indicated by increases in projectile points, quarry usage, and human-related radiocarbon ages.

Introduction

Considerable interest has emerged about the potential effects of abrupt, large-scale climate change on plant and animal populations as well as humans, in part because of growing concerns about potential impacts of modern global warming. Since the end of the last Glacial Maximum ca. 18,000 cal BP, the most pronounced extended climate perturbation following the onset of rapid deglaciation was the Younger Dryas (YD) cooling episode. This began abruptly at ca. 12,900 cal BP (all dates are in calendar or calibrated years before present or BP, unless otherwise noted) and persisted for about 1300 years. Various hypotheses have been proposed to explain the abrupt cooling reversal at the onset of the YD, including shifts in continental meltwater outflow (Kennett and Shackleton, 1975, Broecker et al., 1989, Broecker et al., 2010, Carlson, 2007); outburst flooding (Teller, 1988, Murton, 2010); related changes in thermohaline circulation (Broecker et al., 1989, Alley, 2000); and cosmic impact (Firestone et al., 2007). These hypotheses are the subject of ongoing debate and will not be addressed here. It is well accepted that the onset of the YD led to widespread biotic changes in many parts of the Northern Hemisphere, although specific regional biotic and human responses are not well constrained. Investigations into the YD have led to appreciable recent debate about whether or not a significant decline and/or reorganization in human populations occurred at the onset of the YD ca. 12,900 cal BP (cf., Firestone et al., 2007, Anderson et al., 2008a, Anderson et al., 2008b, Anderson et al., 2009, Anderson et al., 2010, Buchanan et al., 2008, Collard et al., 2008, Meltzer, 2009, Holliday and Meltzer, 2010, Meltzer and Holliday, 2010, Steele, 2010). This paper explores what happened to human populations in North America during the YD using three somewhat interrelated lines of evidence: (1) Paleoindian projectile point frequency data; (2) changes in Paleoindian usage patterns of lithic quarries, and (3) summed probability analyses (SPA) of radiocarbon dates related to human activity. The primary focus of this contribution has been to compile and evaluate data using these approaches to determine whether or not the evidence is consistent with changes in human population at the onset of the YD.

Section snippets

Climate and culture change: basic assumptions

An extensive literature documents how changes in climate affect biotic communities and human societies. Climate parameters such as the type, rate, and magnitude of change help shape the degree of cultural change and may even produce human population bottlenecks. Of particular importance to early human societies was the potential effect of such change on food supplies, and whether this affected the incidence and intensity of epidemics, civil unrest, or warfare (e.g., Fagan, 2000, Fagan, 2004,

Analysis results (1): Clovis and post-Clovis projectile point frequencies in North America

Paleoindian projectile points occur across North America within a number of geographically widespread and variable stylistic horizons (Fig. 1). The ‘Clovis horizon’ is dated to ca. 13,050 to 12,900 cal BP, just prior to the YD onset, and is marked by classic Clovis points, which typically have flat to weakly indented bases and fluting only partly along the blade (Morrow, 1996, Tankersley, 2004, Waters and Stafford, 2007, Meltzer, 2009). This point style was replaced during the early part of the

Analysis results (2): southeastern quarry assemblages

The documentation of Clovis and immediate post-Clovis use of quarry sites in the southeastern U.S. has not been an easy task, and reflects decades of collection and excavation by avocational and professional archaeologists. For the southeastern U.S., records were compiled of archaeological assemblages from eleven major stone quarry sites that were used extensively during the Clovis period and for most of prehistory thereafter. These represent major known quarry sites used by Clovis populations

Analysis results (3): summed probability analyses

Further investigation of possible changes in North American human populations during the last deglacial interval from about 14,000 to 11,000 cal BP used summed probability analyses (SPA). This analysis relies on changes in the frequencies of radiocarbon dates from cultural sites (e.g., Rick, 1987, Housley et al., 1997, Gkiasta et al., 2003, Miller and Kenmotsu, 2004, Gamble et al., 2005, Thomas, 2008, Buchanan et al., 2008, Blockley and Pinhasi, 2011). The procedure involves calibrating

A test of SPA in North America

SPA was first used to test whether or not a long hypothesized decline in human and bison populations on the Great Plains during the Altithermal, or Atlantic period, an extended period of warming during the Mid-Holocene from ∼9000–5000 cal BP, whose effects varied from region to region (Reeves, 1973, Frison, 1978:201; Wedel, 1986, Mayewski et al., 2004, Anderson et al., 2007), could be identified. Available dates from the Canadian Archaeological Radiocarbon Database (CARD, 2005) were divided

Younger Dryas SPA results for North America

The same 14C dates published by Buchanan et al. (2008) and spanning from ∼14,000 to 11,000 cal BP and including the YD interval, were used to analyze multiple regions of North America (Fig. 9). Contrary to Buchanan et al. (2008) and as supported by Steele (2010), there is an abrupt decline at the YD onset at or close to 12,900 cal BP, followed a few hundred years later by a distinct rebound that continued for several hundred years. The decline at the YD onset was more than 50%, similar in

SPA results for North America

Buchanan et al. (2008) recognized a decline in 14C summed probabilities at ∼12,800 cal BP, approximately the time of the YD onset or slightly later, but interpreted that decline as relatively minor, essentially no more significant from other fluctuations observed from ∼13,000 to 9500 cal BP. To evaluate whether or not the decline observed in many areas after ∼12,900 cal BP represented noise, a test was conducted in which the radiocarbon database was divided into several different regions and

SPA results on other continents

Using the radiocarbon databases in Table 2, Table 3, SPA were conducted with cultural 14C dates for other parts of the Northern Hemisphere (Fig. 11) to determine whether or not a decline occurred at the onset of the YD. These results (Fig. 12) are similar to those in North America in some but not all areas (i.e., the Mideast). Apparent population declines or plateaus associated with the YD onset appear in all continental areas north of the equator.

Europe displays a drop in 14C summed

Conclusions

All three datasets, projectile points, quarries, and SPA data, indicate that a major human population decrease (bottleneck), or alternatively population reorganizations (i.e., dramatic changes in settlement patterning), occurred over broad areas of North America at the onset of the YD cooling episode ∼12,900 cal BP. The SPA results provide evidence that similar declines or changes occurred across much of remainder of the Northern Hemisphere with the exception it, seems, of the Middle East. In

Acknowledgments

The authors wish to thank Stuart J. Fiedel, Ted Goebel, Erik Johanson, Shane Miller, Kenneth E. Sassaman, Thomas W. Stafford, Jr., Stephen J. Yerka, and two anonymous reviewers for their advice and comments during the the preparation of this paper. The research reported herein was facilitated by interactions with numerous colleagues in recent years, whose openness and assistance is deeply appreciated. Those interested in furthering the work with PIDBA are encouraged to submit primary data for

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