Spatiotemporal diversification of projectile point types in western North America over 13,000 years

https://doi.org/10.1016/j.jasrep.2019.01.029Get rights and content

Highlights

  • Projectile point type diversity increases exponentially through time.

  • Spatial extent of projectile point types decrease exponentially through time.

  • Projectile point type diversification is a space-filling process.

  • Diversity increases with population growth and increasing temperature over the Holocene.

Abstract

North America was initially colonized by humans during the late Pleistocene, and over the course of the Holocene material culture diversified as local populations adapted to regional environments. However, to date, while anthropologists and archaeologists have long been interested in diversity, little is known of the process of diversification over space and time. Here, we focus on the diversification of the archaeological record of western North America over 13,000 years. By compiling time series of projectile point types and their spatial distribution, we quantify the empirical record of diversification in this region. Our results show that projectile point diversity increases exponentially over time, consistent with a simple evolutionary branching process. The spatial extent of projectile points decreases exponentially over time at a similar rate. Therefore, the evolutionary diversification of projectile point types in western North America is a fractal-like space-filling process, likely reflecting increasingly localized adaptations to regional environments and a consequent reduction in the spatial extent of cultural networks.

Introduction

Understanding diversity and diversification lies at the heart of evolutionary approaches to science. Mathematically, diversification is best modeled as an evolutionary branching process (Karlin, 2014; Kimmel and Axelrod, 2016) where ancestral forms diverge over time in response to the interaction of internal dynamics and external stimuli resulting in the origination of descendent forms, be they biological species or human cultural traits (Henrich and McElreath, 2003; Maffi, 2005; Nettle, 1999; Nunn, 2011). As the human species expanded its range out of Africa, human socioeconomies diversified as populations encountered and adapted to new environments (Hiscock, 2013). Coupled with global-scale climate changes at the end of the Pleistocene, regional technological adaptations led to the modification of ecosystems (i.e., niche construction) that created coevolutionary feedbacks between human populations, their technologies and their environments. In several places around the planet these coevolutionary feedback loops resulted in the increased management and the eventual domestication of plants and animals (Bellwood, 2005). As a result, human cultures, socioeconomies, and social complexity diversified worldwide over time as local adaptations, and their diffusion (Bailey et al., 2012; Bellwood and Renfrew, 2002; Diamond and Bellwood, 2003), led to novel technological, economic, and cultural innovations creating spatiotemporal patterning in the archaeological record.

Social scientists have long been interested in quantifying human cultural diversity. Since the mid-1990s anthropologists have sought to understand the global biogeographic structure of linguistic diversity (Axelsen and Manrubia, 2014; Cashdan, 2001; Collard and Foley, 2002; Currie and Mace, 2012; Gavin et al., 2013; Mace and Pagel, 1995; Maffi, 2005; Nettle, 1999). Similar research has explored ethnic (Ahlerup and Olsson, 2012; Burnside et al., 2012; Cashdan, 2001; Michalopoulos, 2012; Pagel and Mace, 2004), economic (Kummu and Varis, 2011), sociopolitical (Currie and Mace, 2009; Turchin et al., 2018), and mythological diversity (Berezkin, 2005, Berezkin, 2009). Phylogenetic approaches are commonly employed to reconstruct the evolutionary diversification of languages (Atkinson, 2011; Bouckaert et al., 2012; Gray and Atkinson, 2003; Greenhill et al., 2010; Grollemund et al., 2015; Pagel et al., 2007), sociopolitical complexity (Currie et al., 2010, Currie et al., 2013; Walker and Hamilton, 2011), mythologies (d'Huy, 2013a, d'Huy, 2013b, d'Huy, 2013c) and folktales (Da Silva and Tehrani, 2016; Pagel, 2016; Tehrani, 2013).

Others have measured the pace of cultural evolution using archaeological data by quantifying rates of change in artifact form over time (Perreault, 2012). Researchers studying the evolutionary diversification of stone tool technologies, for example, often use morphometric cladistic approaches to measure rates of change in continuous measures of shape, as opposed to the discrete traits required by phylogenetics (Buchanan, 2006; Buchanan et al., 2011; Buchanan and Collard, 2010a, Buchanan and Collard, 2010b; Buchanan and Hamilton, 2009; Costa, 2010; Eren and Lycett, 2012; Iovita, 2011; Iovita and McPherron, 2011; Lyman et al., 2008, Lyman et al., 2009; Lyman and O'Brien, 2000; Mesoudi and O'Brien, 2008a, Mesoudi and O'Brien, 2008b; O'Brien et al., 2001, O'Brien et al., 2002; Thulman, 2012). The resulting evolutionary structure gives insight into the processes of innovation, selection, and drift in the diversification process. Approaches that explicitly consider the spatiotemporal diffusion of technologies and populations use geolocated radiocarbon databases. Here, population expansions, or the diffusion of innovations, are traced through spatiotemporal gradients in the radiocarbon record (Cavalli-Sforza et al., 1993; Collard et al., 2010; Fort, 2012; Fort et al., 2004; Hamilton and Buchanan, 2007, Hamilton and Buchanan, 2010; Pinhasi et al., 2005).

In this paper, we focus on the diversification of stone tool technologies in North America from the initial colonization by humans in the late Pleistocene through the Holocene. Specifically, we examine the spatiotemporal diversification of projectile point types in western North America over a period of about 13,000 years. While the specific timing and nature of the initial colonization of the Americas is an area of active debate (Braje et al., 2017, Braje et al., 2018; Potter et al., 2017, Potter et al., 2018), most experts agree that late Paleolithic hunter-gatherer populations from northeast Asia entered North America via the Bering Land Bridge, first appearing in western Alaska sometime during the late Pleistocene (Hamilton and Buchanan, 2010; Madsen, 2004; Meltzer, 2009). A small founding population later entered the North American continent south of the ice sheets and rapidly expanded across the continent (Hamilton and Buchanan, 2007). Both the genetic and archaeological records show that this small founding population exhibited low levels of diversity. However, recent research shows that early Paleoindian populations had already diversified into distinct, spatially discrete regional variants across North America by ~12,000 cal BP (Buchanan et al., 2016a). Moreover, this diversification suggests an adaptive radiation as regional variation in stone tool technologies and projectile point shapes correlate with regional variation in the body size spectrum of major mammalian prey species (Buchanan et al., 2011).

We chose western North America as our study region as there are various data sets available with which to study diversification over time. First, we summarize the available data. Second, we analyze projectile point type diversification over time. Third, we analyze projectile point type diversification over space. Fourth, we then consider the spatiotemporal dynamics in relation to population growth and regional climate changes over the study period. We also address potential sampling bias in the identification of projectile point types over different time periods.

Section snippets

Projectile point types

We extracted data from Justice's projectile point typologies of the US Southwest (Justice, 2002a), and California and the Great Basin (Justice, 2002b). For each projectile point type, we recorded maximum date (origination) and minimum date (extinction) (Fig. 1), and calibrated them using the calpal Intcal 13 calibration curve (Danzeglocke, 2018). We then digitized the projectile point distribution maps for each type (where available) built shape files of their spatial distribution and measured

Discussion

Our results describe a complex diversification process where, following the initial human colonization of North America and expansion throughout western North America over the late Pleistocene, as temperatures increased over the Holocene, populations grew, innovated, and subdivided into increasingly localized subpopulations. Projectile point diversity consequently increased in proportion to population size, as did the replacement rates of projectile point types.

Cultural diversification of any

Acknowledgements

We thank James Hartley for help digitizing the projectile point spatial extent data and to the anonymous reviewers of the paper whose comments greatly improved the content of the paper.

References (114)

  • M.J. O'Brien et al.

    Cladistics is useful for reconstructing archaeological phylogenies: Palaeoindian points from the southeastern United States

    J. Archaeol. Sci.

    (2001)
  • M.J. O'Brien et al.

    Two issues in archaeological phylogenetics: taxon construction and outgroup selection

    J. Theor. Biol.

    (2002)
  • S.G. Ortman et al.

    Settlement scaling and economic change in the Central Andes

    J. Archaeol. Sci.

    (2016)
  • M. Pagel

    Anthropology: the long lives of fairy tales

    Curr. Biol.

    (2016)
  • B.A. Potter et al.

    Early colonization of Beringia and northern North America: chronology, routes, and adaptive strategies

    Quat. Int.

    (2017)
  • P. Ahlerup et al.

    The roots of ethnic diversity

    J. Econ. Growth

    (2012)
  • Q.D. Atkinson

    Phonemic diversity supports a serial founder effect model of language expansion from Africa

    Science

    (2011)
  • J.B. Axelsen et al.

    River Density and Landscape Roughness Are Universal Determinants of Linguistic Diversity

    (2014)
  • D.H. Bailey et al.

    Latitude, population size, and the language-farming dispersal hypothesis

    Evol. Ecol. Res.

    (2012)
  • D.B. Bamforth et al.

    Technology, flaked stone technology, and risk

    Archeol. Pap. Am. Anthropol. Assoc.

    (1997)
  • P. Bellwood

    First Farmers: The Origins of Agricultural Societies

    (2005)
  • P.S. Bellwood et al.

    Examining the Farming/Language Dispersal Hypothesis

    (2002)
  • Y. Berezkin

    The cosmic hunt: variants of a Siberian-North-American myth

    Folklore

    (2005)
  • Y.E. Berezkin

    Why are people mortal? World mythology and the “out-of-africa” scenario

  • L. Bettencourt et al.

    A unified theory of urban living

    Nature

    (2010)
  • L.M.A. Bettencourt et al.

    Growth, innovation, scaling, and the pace of life in cities

    Proc. Natl. Acad. Sci.

    (2007)
  • L.M. Bettencourt et al.

    Professional diversity and the productivity of cities

    Sci. Rep.

    (2014)
  • G. Bond et al.

    A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates

    Science

    (1997)
  • E. Boserup

    Population and Technological Change: A Study of Long-Term Trends

    (1981)
  • R. Bouckaert et al.

    Mapping the origins and expansion of the Indo-European language family

    Science

    (2012)
  • T.J. Braje et al.

    Finding the first Americans

    Science

    (2017)
  • T.J. Braje et al.

    Arrival routes of first Americans uncertain—response

    Science

    (2018)
  • R.U. Bryson et al.

    A calibrated radiocarbon database of late Quaternary volcanic eruptions

    eEarth Discuss.

    (2006)
  • B. Buchanan et al.

    An assessment of the impact of resharpening on Paleoindian projectile point blade shape using geometric morphometric techniques

  • B. Buchanan et al.

    A formal test of the origin of variation in north American early Paleoindian projectile points

    Am. Antiq.

    (2009)
  • B. Buchanan et al.

    Drivers of technological richness in prehistoric Texas: an archaeological test of the population size and environmental risk hypotheses

    Archaeol. Anthropol. Sci.

    (2016)
  • B. Buchanan et al.

    Investigating the scale of prehistoric social networks using culture, language, and point types in western North America

    Archaeol. Anthropol. Sci.

    (2017)
  • W.R. Burnside et al.

    Human macroecology: linking pattern and process in big-picture human ecology

    Biol. Rev.

    (2012)
  • E. Cashdan

    Ethnic diversity and its environmental determinants: effects of climate, pathogens, and habitat diversity

    Am. Anthropol.

    (2001)
  • L.L. Cavalli-Sforza et al.

    Demic expansions and human evolution

    Science

    (1993)
  • R. Cesaretti et al.

    Population-area relationship for medieval European cities

    PLoS One

    (2016)
  • I.F. Collard et al.

    Latitudinal patterns and environmental determinants of recent human cultural diversity: do humans follow biogeographical rules?

    Evol. Ecol. Res.

    (2002)
  • M. Collard et al.

    Causes of toolkit variation among hunter-gatherers: a test of four competing hypotheses

    Can. J. Archaeol.

    (2005)
  • M. Collard et al.

    What drives the evolution of hunter–gatherer subsistence technology? A reanalysis of the risk hypothesis with data from the Pacific Northwest

    Philos. Trans. R. Soc. Lond. Ser. B Biol. Sci.

    (2011)
  • M. Collard et al.

    Risk, mobility or population size? Drivers of technological richness among contact-period western North American hunter–gatherers

    Philos. Trans. R. Soc. B

    (2013)
  • A.G. Costa

    A geometric morphometric assessment of plan shape in bone and stone Acheulean bifaces from the Middle Pleistocene site of Castel di Guido, Latium, Italy

  • T.E. Currie et al.

    Political complexity predicts the spread of ethnolinguistic groups

    Proc. Natl. Acad. Sci.

    (2009)
  • T.E. Currie et al.

    The evolution of ethnolinguistic diversity

    Adv. Complex Syst.

    (2012)
  • T.E. Currie et al.

    Rise and fall of political complexity in island South-East Asia and the Pacific

    Nature

    (2010)
  • T.E. Currie et al.

    Cultural phylogeography of the bantu languages of sub-Saharan Africa

    Proc. R. Soc. B

    (2013)
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