Late Pleistocene hominin settlement patterns and population dynamics in the Zagros Mountains: Kermanshah region

Abstract

The Middle and Upper Palaeolithic artifacts of the Zagros Mountains are relatively better understood than those in other parts of the Iranian Plateau. However, settlement systems, land use and Palaeolithic population dynamics for this region have received less attention. Here we present research on the study of human behavior that contributes to a better understanding of the early human colonization of Eurasia. Specifically, we focus on the Kermanshah region of the west-central Zagros to evaluate hominin dispersal and adaptation by investigating hominin settlement patterns and behavioral responses to the new and diverse environments and topography of this part of the Zagros region. Our survey in Kermanshah documented over 260 new Palaeolithic localities, enabled us to draw Middle and Upper Palaeolithic site distribution patterns and population dynamics which reveal that this part of the Zagros was intensively populated in both the Middle and Upper Palaeolithic. This research demonstrates that the Zagros in general, and the Kermanshah area in particular, were by no means impassable but include intermountain plains connected to each other by valleys associated with permanent water and raw material sources. Middle Palaeolithic settlements are most abundant in areas with high topographic contrast that contain high mountains, flat plains, and diverse resources. Eventually, the Zagros was one of a handful of important interglacial refugia in south-western Asia for hominins during the Upper Pleistocene and may have served as a core area from which colonizations and recolonizations of Eurasia occurred during multiple dispersals.

Introduction

The Zagros region transcends the borders of modern-day Iran, Iraq and Turkey, and is the largest geological zone of south-western Asia (Fig. 1). Its position, size and orientation places the Zagros at the centre of a human migration ‘crossroad’ between east-west and south-north. It provides critical information for understanding the Palaeolithic settlement of the Iranian Plateau and beyond and is of pivotal importance for models of hominin evolution in south-western Asia. Existing archaeological records for this region indicate a rich record of hominin activity that can elucidate patterns of early hominin migration out of Africa towards Europe and Eurasia. Geographically, the Zagros Mountains are an area of elevated topography, with climatically, geologically and biogeographically variable habitats and ecozones. Hominins would have encountered this area almost immediately upon leaving East Africa, and its complex topography and humid microclimate (Oberlander, 1965) offered a habitat that early hominins had not encountered on the African continent nor in the adjacent regions.

The Zagros region has been somewhat neglected by paleoanthropologists and has, so far, played little role in the story of hominin evolution. This situation partly results from the lack of extensive and purposeful Palaeolithic research in the region due to challenging political and logistical conditions (Heydari-Guran, 2014:1). The dispersed and unequal distribution of Palaeolithic sites across the region, as well as the size of the area, make it difficult to put the missing parts of the puzzle of human evolution together for this region. Consequently, the role of the Zagros is often absent from archaeological theories concerning the hominin dispersal to Eurasia and the evidence of hominin presence underestimated or ignored, or alternatively considered as a mountainous barrier region during late MIS 5, MIS 4 and beginning of MIS 3 the harsh climatic conditions of the Late Pleistocene (i.e. Dennell, 2009, Dennell, 2010, Dennell, 2017; Field and Lahr, 2006). Moreover, theorists argue that the strong presence of Neanderthals in the Zagros region (e.g. Shanidar; Trinkaus, 1983) prevented early anatomically modern humans (AMHs) from entering and establishing populations in the area (e.g. see Boivin et al., 2013). Although questions surrounding the origin of Upper Pleistocene hominins, their dispersal into Eurasia, and their potential relationships with other populations outside of Africa have received much attention (e.g. Boivin et al., 2013; Pagani et al., 2016; Bae et al., 2017), the issue of subsistence strategies and how they evolved in novel environmental contexts with variable habitats remains less explored (Hublin and Richards, 2009). An array of studies has examined the strong and direct relationship between the natural landscape and the distribution and behaviour of terrestrial organisms, including humans (Bailey and King, 2011).

Organisms respond to environmental heterogeneity at different scales and in different ways, and spatial heterogeneity, such as that found in the Zagros region, can influence the movement patterns of organisms (Pickett and Cadenasso, 1995), and thus affect dispersal rates and foraging behaviours even among humans. The mechanics of human movement through a biogeographical landscape can provide a record of how a group searches for, interacts with, and uses heterogeneous resources in response to landscape structure (Romero et al., 2008). Therefore, the different patterns of human movement, activities, and procurement strategies should be considered as a response to different types of landscapes (Heydari-Guran, 2014:4).

To date, the west-central Zagros Mountains includes two hot-spots of Palaeolithic research: the Khorramabad (e.g. Hole and Flannery, 1967; Roustaei et al., 2004; Bazgir et al., 2017) and Kermanshah (e.g. Coon, 1957; Biglari and Taheri, 2000; Biglari and Heydari [Guran], 2001; Biglari, 2001; Biglari and Shidrang, 2016; Shidrang et al., 2016; Mohammadi Ghasiran et al., 2017; Heydari-Guran and Ghasidian, 2017) regions of the Iranian Plateau. In this paper, we focus on the Kermanshah region. Based on the geology, and topographical and climatological conditions, we divided the Zagros into four ecozones of northern, west-central, central and southern. Each ecozone yields several home-range zones. The characteristics of these ecozone and home-range zones are described elsewhere (Heydari-Guran, 2014). The Palaeolithic occupation areas are normally superimposed on the valleys and plains and formed between mountain ranges where major streams course through.

Earlier sporadic studies concerning the Palaeolithic in Kermanshah (e.g. see Smith, 1986, Biglari and Heydari [Guran], 2001, Biglari and Abdi, 1999, Biglari and Taheri, 2000, Jaubert et al., 2006, Heydari-Guran, 2014, Shidrang et al., 2016, Biglari and Shidrang, 2016, Mohammadi Ghasiran et al., 2017) had already putatively revealed that this region could be key in the reconstruction of hominin behaviour and migration. Yet, despite its potential importance, no extensive or research-oriented work, such as that conducted in Khorramabad (Hole and Flannery, 1967; Otte et al., 2007; Bazgir et al., 2017), has been carried out in Kermanshah.

Since 2009, the authors have conducted a project to track early hominin migrations and occupation, and the associated cultural and behavioural attributes in the Kermanshah region (Heydari-Guran and Ghasidian, 2017). Physio-geographically, Kermanshah is an ideal candidate for tackling some of the major outstanding questions for hominin evolution that surround this region, of which three major issues are addressed here:

A) The first, and perhaps most intriguing issue, is the nature and timing of the initial dispersal of hominins from Africa (Bar-Yosef and Belfer-Cohen, 2001; Dennell, 2010). Evidence of Palaeolithic occupation in the area, namely the Gakia hand axe site, dated the earliest occupation at Kermanshah to the Lower Palaeolithic (LP) (Biglari and Heydari [Guran], 2001). This evidence, despite being limited, is related to the Acheulean and could be related to Homo erectus and demonstrates that the Kermanshah region was an attractive habitat for hominins from the early Pleistocene onwards. The evidence of LP in the adjacent area of Mehran Plain (Biglari et al., 2000) further implies that there is a high probability of colonization of the Zagros during the earlier Palaeolithic periods, further supported by evidence of numerous hand axes from the foothills of the northern Zagros Mountains (Heydari-Guran, 2015). To date, no research has been carried out to address the temporal gap between the LP and the beginning of the Middle Palaeolithic (MP). This project, therefore, targets this issue as a period for a major contribution to our understanding of hominin dispersal and evolution in this area, and documents the behavioural and subsistence changes from LP to the Upper Palaeolithic (UP), as well as any evidence of MP industries that predate the Zagros Mousterian.

B) The second issue revolves around hominin evolution during the MP period in the study region. All researchers unanimously dealt with the MP of the Zagros, referred to its cultural tradition as the Zagros Mousterian (Dibble, 1984; Dibble and Holdaway, 1993; Biglari, 2001). Using this term not only limited the industry to the Zagros region but also, inversely, meant that every MP lithic industry of the Central Plateau of Iran was automatically and arbitrarily assigned to this cultural entity (Biglari et al., 2009). Adopting this approach has meant that much of the variability within these MP cultures has been overlooked. It seems that the main obstacle to a comprehensive view of MP diversity, as well as to UP diversity, is the archaeologists' bias. Most of the detailed lithic artefact studies have been performed by specialists who were trained in a European school of thought (Smith, 1986) and were under the influence of the high-quality Palaeolithic research on the European techno-complexes of the Mousterian and Aurignacian. However, we now know that technological diversity and complex dynamics within the MP, no matter how well researched, cannot necessarily be generalized to other parts of the world, especially the Middle East (Kuhn and Hovers, 2006:4). Research on the MP industries of the other parts of the country (i.e. Central Plateau of Iran) has revealed considerable variability among the MP lithic assemblages, not just in the Zagros Mousterian, but across all MP techno-complexes (Heydari-Guran et al., 2015). The MP variability in the Iranian Plateau is of great importance while it is likely that the Neanderthals occupied highlands of Zagros during MIS 5 and 4, the rest of the plateau could be colonized by other hominins including early modern human.

C) The third issue is the chronology of the MP/UP occupation of the Zagros region. Despite Smith's (1986) emphasis on this problem, so far our knowledge of the actual age of the MP and UP in this region has not improved over the past four decades. Absolute dates for the MP of the Zagros come from the high altitude shelter site of Houmian (ca. 2000 m asl) in Kuhdasht region of the west-central Zagros (Bewley, 1984) dating to 123 kya +3400/−3200 years ago based on thorium‑uranium on a bone fragment, and Mar Tarik Cave in Bisetun (Jaubert et al., 2006) dating to 148 ± 35 kya years ago (see map 1 for the location of the sites in the Zagros and Table 1). However, the latter comes from a stalagmite at the base of the archaeological sequence and is not directly related to the material culture in the cave. Nevertheless, in light of the new data on the MP of the Zagros, these dates appear to be inconsistent with the actual reality of MP in Zagros.

Compared to the MP, the UP dates provide a more complete timeframe of activity across the Zagros Mountains. These dates are available from Shanidar Cave in the northern (Solecki, 1963), Yafteh and Kaldar Caves in the west-central (Hole and Flannery, 1967, Otte et al., 2011, Bazgir et al., 2017), and Ghār-e Boof in the southern Zagros (Ghasidian, 2014). The Bayesian modeling for the UP occupation of the Zagros indicates the UP occupation of the region began approximately 45,000 years ago (Beccera-Valdivia, 2017). In the lack of absolute dating on important sites like Warwasi Rockshelter (Olszewski, 1999), lithic techno-typological analysis evaluates the periods of occupations in the site. The UP occupation at Ghār-e Boof and Shanidar was slightly older than the west-central Zagros Mountains namely at Yaftehat Yafteh Cave (Ghasidian et al., 2019) (Table 1).

D) The last issue addresses the fascinating and complicated matter of the MP to UP transition. This issue is specifically important since it addresses the questions related to MP diversity (i.e. Rolland and Dibble, 1990; Shea, 2003), human replacement and admixture events between anatomically modern humans and other hominin groups during Late Pleistocene in Eurasia (Prüfer et al., 2014. Bae et al., 2017), and the “UP revolution” (Bar Yosef, 2002). During the early Upper Pleistocene, the west-central Zagros ecozone sites are characterized by the presence of rich Levallois/Mousterian artefacts of the MP (probably made by Neanderthals, ca. 60 kya; Solecki, 1963) and burin and blade industries of Baradostian (probably made by AHMs, ca. 40 kya; Solecki, 1958) in the UP period. But among these sites, just two - Ghar-e Khar Cave (Shidrang et al., 2016) and Warwasi Rockshelter (Braidwood and Howe, 1960) - yielded complete sequences spanning from the MP to the Epipalaeolithic. Other sites such as Mar Tarik (Jaubert et al., 2006) and Kobeh Cave (Marean and Kim, 1998) are both associated with a single occupation layer attributed to the MP. These assemblages have been interpreted as evidence for either cultural exchange between incoming UP people and indigenous MP groups or “transitional” phases of the in-situ evolution of local MP culture (Shidrang et al., 2016; Tsanova, 2013). However, researchers have cautioned that the lithic assemblages from these sites may have been artificially mixed through the lumping of distinct strata during excavations. For instance, in Warwasi there was no evidence of a gradual transition from MP to UP visible in the lithic techno-typological traits and the UP characteristics were considered rather intrusive to the region (Ghasidian et al., 2019; Tsanova, 2013; Hole personal communications 2016).