Human Population Dynamics and the Emergence of Microblade Technology in Northeast Asia during the Upper Palaeolithic: A Current View

Abstract

The widespread distribution of microblade assemblages has been discussed in connection with human migration and cultural transmission across Northeast Asia during MIS 2. However, there has been no clear consensus among researchers on the interrelationships between the emergence of microblade assemblages and the construction of human population dynamics in Northeast Asia. Recent evidence makes systematic verification still necessary to determine whether the scenario of simple migration from North Asia is sufficient to explain spatiotemporal variation in lithic assemblages in different regions of Northeast Asia. Elucidating the diversity of reduction processes and knapping techniques among lithic assemblages across Northeast Asia is important for understanding of human population dynamics. This chapter reviews the current state of the study of microblade technology in Northeast Asia, focusing on the issues of the definition of microblades and microblade technology and their impacts on the current interpretations.

1. Introduction

Upper Palaeolithic lithic assemblages containing microblades are distributed across a wide area of Northeast Asia, including Northern China, the Korean Peninsula and the Japanese archipelago, during the marine isotope stage (MIS) 2. Elucidating the features of microblades and the processes of production is an interesting task for research to understand the structures of the tool equipment used by hunter-gatherers during this period. The roles that microblades and microblade technology played are a central focus of research among archaeologists studying hunter-gatherers’ behavioural strategies during the Late Pleistocene in Northeast Asia [1].

The widespread distribution of microblade assemblages has been discussed in connection with human migration and cultural transmission across Northeast Asia during MIS 2. Indeed, recent archaeological evidence has shown that significant techno-typological changes in lithic assemblages occurred throughout Northeast Asia at the beginning of MIS 2, and this enabled us to infer the occurrence of large-scale population movements and/or cultural diffusion [2, 3, 4]. The genetic analysis of ancient human fossils also suggests that several migration events occurred in North and Northeast Asia during MIS 2 [5]. Understanding the emergence of microblade assemblages would have important implications for explaining spatiotemporal changes not only in lithic production technology and function but also in human population dynamics across North and Northeast Asia.

However, there has been no clear consensus among researchers on the emergence and development of microblade assemblages in Northeast Asia until recently. The discrepancy between the definitions of a microblade and microblade technology led to confusion [6, 7]. It is more complicated than might be expected to define microblades and microblade technology. Previous works have tended to downplay the significant differences present in the definitions of these concepts and their impacts on the interpretations of the emergence of microblade technology and the construction of a robust archaeological approach to past population movements and/or cultural diffusion. This chapter reviews the current state of the study of microblade technology in North and Northeast Asia, focusing on the issues of human population dynamics reconstruction and the definition of microblades and microblade technology.

2. Microblade technology and human population dynamics

In the study of microblade assemblages in Northeast Asia, archaeologists have focused on techno-typological classifications of microblade cores and associated stone tools (e.g., burins), as well as their spatiotemporal variation for constructing cultural sequences. An emphasis on defining detailed classifications (or methods) for microblade reduction sequences has emerged [8]. Recent decades have witnessed rapid progress in the accumulation of radiocarbon dates associated with lithic assemblages at various sites in Northeast Asia. Some clear differences of opinion have emerged regarding the reliability of radiocarbon dating [9, 10], but consensus among researchers has been established in recent years regarding the importance of accurate and precise chronologies and a higher density of dates. This consensus has led to the construction of chronological frameworks at different sites and has given rise to a range of discussions regarding diachronic transitions within a region and in relation to correlating material culture across regions (e.g., [4, 6]).

Reconstructed cultural histories for the regions of Northeast Asia from MIS 3 to MIS 2 are as an important source of information for understanding human population dynamics during this period. Studies of microblade technology at and before the Last Glacial Maximum (LGM; 26.5–19.5 cal. ka) [11] have described population movements across regions of Northeast Asia. One scenario that has garnered attention is that microblade technology (this technology is referred by researchers in different ways, for example, morphometrically, technologically and functionally) that was distributed across North Asia (Siberia and Mongolia) during the latter half of MIS 3 [12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22] spread southward as a result of environmental changes taking place from the beginning of MIS 2 that led to the emergence of the Northeast Asian initial microblade assemblages (NAIMA) in Northern China, on the Korean Peninsula and on the Palaeo-Sakhalin-Hokkaido-Kuril (PSHK) Peninsula [2, 3, 4], although this has been disputed [7, 23]. A similar scenario regarding large-scale human migration from the beginning of MIS 2 caused by environmental changes is also hypothesised for Western Europe, where human populations moved southward from high-latitude regions [24, 25, 26, 27]. Focusing on population dynamics as a response to environmental changes in MIS 2 and making comparisons among different cases may provide important implications for the interrelationships between humans and the environment during environmental change.

If we assume that the emergence of microblade technology in Northeast Asia reflects large-scale human population migration, we must also determine how far this hypothesis is consistent with the results of genomic research. In recent years, several major papers have been established to demonstrate human genomic diversity during the Palaeolithic. Genome analysis in palaeoanthropological studies provides evidence for human population history and structures that are independent of any analysis of the archaeological record. For this reason, the debate over the relationship between the results of palaeoanthropological genome analysis and those of archaeological lithic analysis has become ever more important for understanding human population dynamics during the Pleistocene (e.g., [28]).

Recent findings of ancient DNA have indicated a scenario according to which Homo sapiens populations that had spread eastward in the northern part of the Eurasian continent and were distributed across North Asia (i.e., Ancient North Eurasians and Ancient North Siberians) came into contact in Northeast Asia with populations of Homo sapiens that had spread eastward across southern Eurasia and were distributed in East Asia (i.e., East Asians). This scenario grounds the hypothesis that the populations that had spread to the Americas diverged in a similar process to that described above [5, 29, 30, 31, 32, 33]. It remains to be definitively shown in what period and region this contact began and the archaeological phenomena to which it corresponds. However, it can be predicted that the archaeological emergence of microblade technology in Northeast Asia from the beginning of MIS 2 is closely related to the population history described above. Further study of NAIMA will yield evidence for the discussion of the relationship between population dynamics and cultural histories in Palaeolithic archaeology.

The assessment of two particular phenomena has greatly influenced the establishment of the above-mentioned hypothesis regarding the emergence process of NAIMA. The first regards the extent of the impact of cooling on population movements in Northeast Asia during the LGM. In particular, several studies have noted that the number of archaeological sites in Southern Siberia decreased during the LGM, and the region was temporarily unoccupied [34, 35, 36, 37, 38]; recognition of this has played a major role in the formation of the hypothesis presented here. Second, from the onset of MIS 2, across various regions of Northeast Asia, significant changes occurred in types of stone tools and in lithic production technology (e.g., [39, 40, 41, 42, 43]). The elucidation of cultural sequences in Northeast Asia has produced significant results regarding the interpretation of population dynamics during the LGM, which is specifically linked to the possibility that human population migration occurred. Research has also focused on the dispersal of microblade technology as a link between phenomena recognised in Northeast Asia.

For several decades, the central theme of archaeological research on the Palaeolithic period has been developing an understanding of the spatiotemporal diversity of lithic assemblages and their formation. As a result of these investigations, many archaeological interpretations of the Palaeolithic record rely on changing environments and its impact on the supposed movement of human populations. Indeed, it is often argued that population movements are responsible for changes in the archaeological record, such as in the case of NAIMA. However, other researchers have proposed criticisms of the theoretical and empirical basis for the use of distinctive sets of artefacts as proxies for past populations [44, 45, 46]. A recent point of controversy related to the question whether similarities in material culture across different regions reflect migration, diffusion (cultural transmission) or convergent evolution among human populations and the basis on which to distinguish these factors (e.g., [47, 48, 49]). Furthermore, frameworks of cultural history that understand diachronic transitions within a region as reflecting movements of human populations must be reconsidered, as increased interactions between different populations can lead local cultures to rapidly evolve and attain greater complexity [50]. Thus, the simple explanation that the spatiotemporal distribution of similar typological and technological sets corresponds to the distribution of specific human populations is no longer valid. We are thus far from being able to make reliable inferences regarding human population movements and/or cultural diffusion in the Upper Palaeolithic of Northeast Asia. We now need to develop better ways of thinking about human population dynamics and changes in material culture in Northeast Asia from MIS 3 to MIS 2 taking into consideration the diversity of factors that structure the archaeological record.

3. Microblade and microblade technology: definitions

Various ideas have been proposed by many researchers regarding the definitions of microblades and microblade technology, and this has led to considerable confusion in the debate. The following indicators are used in those definitions:

1. morphometric features, such as the size or shape of the side edges and ridges (e.g., [51, 52]);

2. tool function, indicated by whether the microblades were inserted into slots grooved along the sides of wood, antler or bone projectile armatures, as well as used as knives or sickles (e.g., [53]);

3. systematic production of microblades from prepared cores, including boat-shaped cores or wedge-shaped cores (e.g., [54, 55]); and

4. specific knapping technique for the removal of microblades, that is, application of pressure knapping techniques (e.g., [6, 56, 57]).

In practice, these indicators are used both individually and in combination with each other in the definitions. There is a direct link between differences in definitions and differences in the understanding of the spatiotemporal distribution of microblade technology or the formulation of scenarios for the emergence and development of microblade technology. It is important to understand the differences and implications of each definition chosen.

These definitions are important aspects of the understanding of the characteristics of microblade technology. However, they present problems for the assessment of the spatiotemporal variability of microblade technology and with regard to what can be identified from an archaeological record. The validity and significance of archaeological definitions should be examined, including whether these definitions can be based on the available archaeological record.

First, microblades inserted in slot grooves along the sides of antlers have been recovered from a few Upper Palaeolithic sites in Siberia [58, 59]. However, except for these cases, no artefacts have been found in the condition in which the microblades of the Upper Palaeolithic were used. In addition, although there has been some use-wear analysis of microblades in the Upper Palaeolithic of Northeast Asia [60, 61, 62, 63, 64, 65, 66], their diversity in time and space has yet to be elucidated. Microblades are widely distributed across a wide range of natural environments in Northeast Asia, so it is unreasonable to assume a single limited function for them. Functional definitions alone cannot identify microblades or microblade technology from the archaeological records distributed across Northeast Asia; thus, they should be supplemented by definitions that are based on morphometric features.

Second, some researchers have adopted definitions that emphasise standardised sequences in the production of microblades, with the use of wedge-shaped or boat-shaped cores as useful indicators. This has been regarded as a useful approach for understanding changes in technology and behaviour in specific regions and periods within Northeast Asia. However, this framework is not a valid indicator of the diversity of microblade technology found throughout Northeast Asia. In fact, in Northern China and across the Japanese archipelago, there is widespread evidence of reduction processes through which microblades were produced not only from wedge-shaped and boat-shaped cores but also from pyramidal, cylinder and narrow-faced cores (e.g., [4, 40, 67, 68]). Some cases also exist in which multiple reduction sequences of microblade cores co-occur in a single lithic assemblage, which illustrates the importance of elucidating technological relationships among the different processes. To establish an appropriate framework to elucidate population dynamics in MIS 2, an assessment is necessary of the diversity of microblade technology and the technological relationships between lithic assemblages distributed over the wide area from North Asia to Northeast Asia.

Third, the importance that the pressure knapping technique has as an indicator of technological change is undeniable [69]. However, whether this technique is identifiable in the archaeological record remains another matter. For several decades, various techno-morphological criteria for identifying the pressure knapping technique have been proposed in relation to replicative pressure debitage experiments [6, 56, 69, 70, 71, 72]. The main criteria presented here are as follows:

1. edges and dorsal ridges: straight, parallel;

2. profile: very thin, equal thickness, barely curved or straight with a curved distal part, with feathering terminations;

3. bulb attributes: short and pronounced, with a discrete lip under the butt;

4. butt: thick but small, punctiform, narrower than the maximum width of the microblade, rapidly broadening to reach the maximum width;

5. hackle: well pronounced;

6. impact point: perceptible but almost merging with the platform;

7. no obvious ripples on the lower face;

8. abrasion of the overhang, extending to the debitage surface.

These criteria have been widely used to determine the results of pressure knapping techniques over a vast geographical area, thereby enabling an insightful comparison of lithic artefacts. However, their reliability has not been quantitatively verified; therefore, these criteria are somewhat ambiguous in their application. The question also remains whether the indicators that are obtained in experiments can be generalised across different lithic raw materials. Recently, the authors proposed a different means of identifying knapping techniques focusing on fracture wings [73, 74]. These are microscopic markings that are observable on the fracture surfaces of brittle materials and are quantitative indicators of crack velocity [75, 76, 77]. Some attempts have been made sporadically to introduce the analysis of these microscopic fracture features into archaeological lithic studies [78, 79, 80, 81]. Fracture wing analysis enables us to identify knapping techniques in the microblade lithic assemblages of Northeast Asia. However, at present, this method is only applicable to obsidian artefacts and can only be used in the analysis of artefacts that have been excavated from archaeological sites over a limited area.

To allow for a comprehensive discussion based on lithic records from various regions, concepts used to classify and describe archaeological materials should be distinguished from those used for behavioural interpretation. Therefore, to investigate the spatiotemporal variation of lithic assemblages across North and Northeast Asia from MIS 3 to MIS 2, the research could, first, define a microblade according to morphometric criteria (microblade refers to parallel-sided small artefacts possessing one or more ridges running parallel to their long axes, generally 4–10 mm wide and 1–2 mm thick) [82] and select the lithic assemblages to be analysed from that definition. From these, the diversity and interrelationship of microblade technology across various regions should be investigated using technological and functional perspectives.

4. Northeast Asian initial microblade assemblages

In recent decades, a series of discoveries of lithic assemblages chronologically attributed to the first half of MIS 2 continued in Northern China (Northeast and North China), the Korean Peninsula and the PSHK Peninsula (Figure 1). Radiocarbon dating provides reliable chronological positioning for the NAIMA. This chapter evaluates the lithic assemblages chronologically located between the beginning of MIS 2 and approximately 22.5 cal. ka as NAIMA. This period corresponds to the stage in which microblade technology first emerged and became dispersed into the various regions of Northeast Asia. This period also corresponds to a time of declining numbers of sites in Southern Siberia and Mongolia; the number of sites with microblade assemblages increases in these regions only after 22.7 cal. ka (e.g., [38, 83, 84].

Figure 1.

Locations of important sites discussed in the text. 1: Ust-Karakol-1, 2: Anui-2, 3: Tuyana, 4: Torbol-15, 5: Dororji-1, 6: Xishantou, 7: Helong Dadong, 8: Xishahe, 9: Youfang, 10: Longwangchan, 11: Shizitan, 12: Xiachuan, 13: Xishi, 14: Dongshi, 15: Jangheung-ri, 16: Samgeo-ri, 17: Hopyeong-dong, 18: Shinbuk, 19: Kashiwadai-1, 20: Pirika-1, 21: Shimaki, 22: Kawanishi-C.

4.1 Northern China

Some researchers have previously suggested that microblade technology originated in a local microlithic tradition in Northern China [85, 86, 87, 88, 89]. However, more recently, the definition of microblade technology has been revised from a technological perspective, and the accumulation of evidence from various archaeological sites has produced a new understanding regarding the emergence of microblade technology. The prevalent understanding in recent years is that microblade technology has emerged in Northern China since the beginning of MIS 2.

In Northern China, NAIMA have been found at layer 3 of the Xishantou site in Heilongjiang Province [90], at layers 3 and 4 of the Helong Dadong site in Jilin Province [91, 92], at layer 3A of the Xishahe site [93] and the Youfang site [94, 95] in Hebei Province, at layer 7 of the Shizitan S29 site [57, 96, 97] and at layer 2 of the location of Xiaobaihua-Geliang of the Xiachuan site in Shanxi Province [98], at layer 6–5 of the Longwangchan site in Shaanxi Province [99, 100] and at the Xishi and Dongshi sites in Henan Province [42, 65, 101, 102]. Lithic assemblages with dating values equivalent to NAIMA were excavated at the Xiachuan site in the 1970s and 1980s [103, 104, 105, 106]; however, the reliability of the dating values is unknown, as is the context in which the dating samples were obtained. As such, their integration as lithic assemblages remains unclear [107]; and hence, they are not discussed here.

Layer 3 of the Xishantou site, located in the Sanjiang Plain of Northeast China, has been dated to 28.3–27.5 cal. ka; this is the oldest dating in NAIMA in Northern China. The lithic assemblage of this layer is characterised by various shapes of microblades and narrow-faced microblade cores that are made from thick flakes (Figure 2). It is not yet known whether these microblades were produced by pressure knapping. The composition of the lithic assemblage includes side-scrapers, drills and thick core-scrapers, similar to the artefacts found in the microblade lithic assemblages of MIS 3 in North Asia. The geographic location of the site enables the assumption of a relationship with stone tool assemblages from Southern Siberia and Mongolia.

Figure 2.

Artefacts from the Xishantou site. A: blade core, B: microblade core, C–F: microblades, G: blade, H: side-scraper, I: drill. Illustrations adapted form [90].

Layer 4 of the Helong Dadong site, which is located in the northern part of the Changbai Mountains, has been dated to 25.9–25.4 cal. ka, and several wedge-shaped microblade cores are found at the layer 3. Thus, the microblade lithic assemblage from this site is slightly later than around 25 cal. ka. Wedge-shaped obsidian microblade cores are associated with transverse-type burins. These techno-typological features have more in common with the NAIMA of the Korean Peninsula and Hokkaido, which are described below, than with the other microblade lithic assemblages that are distributed in North China. Thus, the Changbai Mountains should be considered as an important area for understanding the routes across which microblade technology spread to the Korean Peninsula and the PSHK Peninsula.

In North China, layer 3A of the Xishahe site has been dated to 27.4–26.6 cal. ka, layer 7 of the Shizitan 29 site to 26.1–23.4 cal. ka, layer 6–4 of the Longwangchan site to 29.3–24.4 cal. ka, layer 2 of the location of Xiaobaihua-Geliang of the Xiachuan site to 28.3–22.4 cal. ka, layer 2c of the Xishi site to 26.5–25.8 cal. ka and layer 2b of the Dongshi site to 28.5–27.1 cal. ka (Figure 3). No microblade lithic assemblages have been identified in layer 3B (29.1–28.2 cal. ka) of the Xishahe site, which is located below layer 3A, at which microblade lithic assemblages have been found [93]. The data from the Xishahe site are important for understanding the period in which microblade lithic assemblages first appeared in North China. Some of the oldest dating values for NAIMA were obtained at the Longwangchan site. However, this should be used with caution, as these certain inversions are seen between the depth of the samples and the subdivision stratigraphy on the one hand and the measured radiocarbon dates on the other. Considering the measured values in combination, it is reasonable to conclude that microblade lithic assemblages appear from 27.5 cal. ka. These data indicate that microblade lithic assemblages appeared in North China at the same time as or slightly later than in Northeast China. Among NAIMA from North China, microblades are produced from various types of microblade cores, namely narrow-faced, boat-shaped, pyramidal, cylinder and wedge-shaped cores. Significant variation between sites is observed in the techno-typological characteristics of the microblade cores and their combinations. The NAIMA in North China is characterised by the lack of bifacial reductions used for wedge-like core pre-forming [102].

Figure 3.

Plot of the radiocarbon dates (cal. BP, 2σ) of the NAIMA in Northeast Asia. 1: Xishantou, 2: Xishahe, 3: Shizitan S29, 4: Longwangchan, 5: Xiachuan (the location of Xiaobaihua-Geliang), 6: Xishi, 7: Dongshi, 8: Jangheung-ri, 9: Hopyeong-dong, 10: Dajeong-dong, 11: Shinbuk, 12: Samgeo-ri, 13: Shimaki, 14: Kawanishi-C, 15: Kashiwadai-1, 16: Pirika-1.

Recent findings identified that the emergence of microblade lithic assemblages in Northern China in the first half of the LGM or slightly earlier. The production of microblades is characterised by not only wedge-shaped and boat-shaped microblade cores but also by cylinder, narrow-faced and pyramidal microblade cores. Some lithic assemblages represent a process of reduction that combines different types of microblade cores; therefore, they should not be studied separately. In addition, the possibility that the NAIMA of Northern China contain some microblades produced by direct percussion and by pressure should be discussed [3, 90, 93]. To discuss the dispersal process of pressure knapping technique in Northeast Asia, an analysis to identify knapping techniques in the lithic assemblages of Northern China is of critical importance.

4.2 The Korean peninsula

Due to the geographical environment, efforts to understand the emergence of microblade technology for the Korean Peninsula have focused on identifying an integrated relationship with Southern Siberia, Mongolia and Northern China [108]. On the Korean Peninsula, NAIMA have been discovered at the Jangheung-ri site, layer III of the Hopyeong-dong site, the Dajeong-dong site, the Shinbuk site and the Samgeo-ri site [109, 110, 111, 112, 113, 114]. These lithic assemblages have been dated to 29.9–27.5 cal. ka at the Jangheung-ri site, 26.0–19.1 cal. ka at layer III of the Hopyeong-dong site, 23.9–23.3 cal. ka at layer III of the Dajeong-dong site, 30.0–25.0 cal. ka at the Shinbuk site and 29.8–28.4 cal. ka at the Samgeo-ri site. The dating for the NAIMA obtained at layer III of the Hopyeong-dong and Shinbuk sites exhibit wide variation in the measured dates. Future research should investigate the validity of the proposed time range, taking into account the formation of the sites. Instead, it is notable that the radiocarbon dates of the lithic assemblages at the Jangheung-ri and the Samgeo-ri sites are slightly older than those of the microblade lithic assemblages in Northern China. This has attracted attention in estimating the place of origin of microblade lithic assemblages in Northeast Asia [23], but it is not appropriate to discuss this issue solely on the basis of their dates without considering the techno-typological characteristics of the lithic assemblages and the spatial and vertical relationships between the lithic artefacts and the dated samples within the sites. Further verification is required to clarify the reliability of the dates of the lithic assemblages and its techno-typological evaluation within Northeast Asia.

Microblades produced from wedge-shaped microblade cores, characterised by a systemic preparation of microblade core blanks, are a common feature of NAIMA on the Korean Peninsula [49, 113, 115]. These lithic assemblages are associated with end-scrapers, side-scrapers and burins that are made from blades and flakes. They share commonalities with the lithic assemblages found in the northern part of the Changbai Mountains in Northeast China and the PSHK Peninsula. Furthermore, the lithic assemblage from the Samgeo-ri site shows a different reduction process of obsidian microblades than that of wedge-shaped microblade cores [114]. Although a detailed analysis is needed in the future, this provides an important case for understanding the technological diversity of NAIMA in the Korean Peninsula.

4.3 The PSHK peninsula

For a long period during the Late Pleistocene, Hokkaido was part of the PSHK Peninsula that was connected to continental Asia [116]. This connection with the mainland may have caused repeated movements of human and faunal populations from the north, especially during colder periods. Several species of large mammals, including mammoths and bison, inhabited the PSHK Peninsula during the LGM [117, 118]. The emergence of NAIMA in MIS 2 in Hokkaido appears to have arisen in the context of this geographical and ecological environment.

The Eniwa-a (En-a) tephra, which erupted in 21–19 cal. ka, is distributed from central to eastern Hokkaido [119]. This tephra forms a useful key bed for dating lithic assemblages. Microblade lithic assemblages, recognisable as belonging to NAIMA are found at various locations within Hokkaido. However, only the Shimaki, Kawanishi-C, Kashiwadai-1 and Pirika-1 sites can be reliably dated because these are the only sites that are found from the lower levels of En-a or for which radiocarbon dates have been obtained that likely indicate the age of the lithic assemblages [120, 121, 122, 123].

Microblade technology in the narrow sense is observed in the lithic assemblages that are found at the lower layers of the Kashiwadai-1 and the Pirika-1 sites. These lithic assemblages include several standardised microblades that are produced from wedge-shaped microblade cores (Figure 4). It is also noteworthy that all of the microblade cores were produced by the systemic shaping of blanks. They are associated with end-scrapers, burins and drills, all of which are made from formal blades. In addition, stone beads, which did not appear before the appearance of NAIMA in the PSHK Peninsula, have been found at these sites [124]. Radiocarbon dates of 25.5–23.5 cal. ka have been obtained for the Kashiwadai-1 site and 25.7–23.4 cal. ka for the lower layer of the Pirika-1 site.

Figure 4.

Artefacts from the Shimaki, Kawanishi-C and Kashiwadai-1 sites. A–D: microblade core and microblades from the Shimaki site, E: boat-shaped microblade core from the Kawanishi-C site, F–G: wedge-shaped microblade cores from the Kasiwadai-1 site. Illustrations adapted form [121, 122, 123].

At the Shimaki and Kawanishi-C sites, microblade or microblade-like debitages have been excavated, albeit in small numbers, along with the narrow-faced and boat-shaped cores that produced them (Figure 4). However, the microblades do not exhibit a regular form, and the morphology of the microblade cores is also notably diverse. It seems likely that neither of these lithic assemblages demonstrates the removal of microblades using the pressure knapping technique [70]. Dating of 26.6–25.8 cal. ka is reported for the Shimaki site [125] and 26.1–25.3 cal. ka for the Kawanishi-C site [122]. The lithic assemblages at these two sites are slightly older than the lithic assemblages at the Kashiwadai-1 and the Pirika-1 sites. Nevertheless, the dating values are close to one another, and thus, the possibility that the two sites overlapped in time cannot be ruled out.

The lithic assemblages excavated at the Shimaki site include several end-scrapers made from flakes, whereas those excavated at the Kawanishi-C site include end-scrapers, side-scrapers and burins that are made of blades and flakes. Stone beads have not been recovered from either site, but the use of pigments has been confirmed. Significant differences exist between the lithic assemblages excavated from the lower layers of the Kashiwadai-1 and the Pirika-1 sites in terms of the reduction processes observed and the composition of the lithic types. Several studies have indicated that the lithic assemblages excavated from the Shimaki and Kawanishi-C sites are not microblade lithic assemblages [126, 127, 128]. Differences in evaluation occurred due to the inclusion of the use of the pressure knapping technique in the definition of microblades and microblade technology.

The emergence of microblade technology in the narrow sense that is observed in the lower layers of the Kashiwadai-1 and Pirika-1 sites is accompanied by changes in the general composition of stone tool types and the appearance of beads. Many researchers support the interpretation that these rapid cultural changes reflect human migrations. However, no clear consensus has yet been reached regarding the emergence of the types of lithic assemblages seen at the Shimaki and Kawanishi-C sites. Even if we were to hypothesise that the emergence of microblade technology in the narrow sense was due to populations migrations from other areas, it is important to determine how this is connected with lithic assemblages such as those at the Shimaki and Kawanishi-C sites. The evidence at these sites strongly suggests that the emergence of NAIMA in the PSHK Peninsula should be considered in terms of the migration of human populations and the process of contact and cultural transmission between migrating and indigenous local populations.

5. Discussion

Recently, it has become increasingly possible to compare the date of appearance and techno-typological characteristics of microblade technology across regions. This indicates that there were significant changes in the typological and technological features of the lithic assemblages seen in Northeast Asia from the latter half of MIS 3 to MIS 2 that can be linked to the emergence of microblade technology [129, 130, 131, 132].

Some researchers have interpreted the evidence to show that microblade technology emerged in Northeast Asia from its dispersal from North Asia, including Southern Siberia and Mongolia, reflecting the migrations of human populations (e.g., [2]), despite some claims to the contrary (e.g., [7, 23]). This interpretation requires a discussion of the relationship between bladelet/microblade technology in Europe, West Asia, Central Asia and North Asia during the early Upper Palaeolithic. The emergence of microblade technology in Northeast Asia is related to a sudden cultural transformation in the cultural sequence from MIS 3 to MIS 2; it is easy to understand how this could be interpreted to indicate migrations of human populations. However, evidence obtained in recent years makes systematic verification still necessary to determine whether the scenario of simple migration from North Asia is sufficient to explain spatiotemporal variation in lithic assemblages in different regions of Northeast Asia.

Microblade technology appeared in Northeast China and the Korean Peninsula at 30–28 cal. ka and appeared at approximately the same time or slightly more later in North China. NAIMA in Northern China and the Korean Peninsula show that microblades were produced from diverse microblade cores, including wedge-shaped, boat-shaped, narrow-faced, cylinder and pyramidal form concepts. These concepts of microblade reduction are technologically interrelated and constitute microblade technology in a given lithic assemblage. For this reason, attempting to define microblade technology using wedge-shaped cores alone makes it quite difficult to understand the technological diversity and interrelatedness of microblade technology in Northern China. In addition, it is particularly noteworthy that different knapping techniques, including direct percussion and pressure, may have been used in the production of microblades in the NAIMA in Northern China and the Korean Peninsula. This suggests that a microblade cannot be defined solely as a product of pressure knapping. Although quantitative analysis of the identification of knapping techniques is required to determine how the microblades were produced in specific lithic assemblages, it is probably only in North Asia that the percussion technique (Mode A) and the pressure technique (Mode B) [70] of microblade production can be clearly distinguished in the temporal sequence.

When the possibility of southward migration by human populations from North Asia is considered, emphasis has been placed on gaps in the number of archaeological sites in North Asia during the LGM [9, 34, 35, 36, 133, 134]. Examination of radiocarbon dates confirms that there is no record of human activity during 24.8–22.7 cal. ka in the trans-Baikal region of Southern Siberia [80]. Although the specific dating may be slightly different, similar trends are seen in the Enisei River basin and Mongolia [10, 37, 135]. If this chronological gap is supported, the periods that did not feature human habitation during the LGM in Southern Siberia and Mongolia cannot be directly correlated with the emergence of microblade technology in Northeast Asia, as shown in the cases of Northern China and the Korean Peninsula. If we hypothesise that the emergence of microblade technology after 30–28 cal. ka in Northern China and the Korean Peninsula was a development of the southward migration of human populations from North Asia due to the cooling of the climate, we must also discuss the extent to which this hypothesis corresponds with high-precision data on palaeo-environmental changes from Southern Siberia to Mongolia and Northern China [136, 137].

If the dispersion of microblade technology from North Asia was a result of migrations of human populations, we must then ask whether this can be limited to one instance of migration or there were several migrations. If there were several migrations from North Asia, then the southward movements of human populations due to cooling during the LGM may be reflected in the changes that are observed in NAIMA from 25 cal. ka. To answer this, we must analyse the spatiotemporal variations in stone tool technology seen in NAIMA and compare them with the lithic assemblages of North Asia. However, we do not yet have a clear understanding of the cultural sequence in North Asia from the early Upper Palaeolithic (39–28 cal. ka) to the middle Upper Palaeolithic (28–22 cal. ka), as research has not yet succeeded in accumulating reliable dating data or verifying the integration of lithic assemblages [138]. Consequently, it is difficult to make comparisons with the lithic assemblages of Northeast Asia.

NAIMA excavated in Northeast Asia include lithic assemblages featuring microblade technology that consists of wedge-shaped microblade cores with carefully prepared blanks that are distributed across the northern part of the Changbai Mountains in Northeast China to the Korean Peninsula and the PSHK Peninsula. There are clear technological differences between these microblade lithic assemblages and those distributed across North Asia in MIS 3 (Ust-Karakol-1, Anui-2, Tuyana, Torbol-15 and Dororji-1) [13, 14, 15, 16, 139, 140, 141], where microblades were produced using a range of reduction processes characterised by boat-shaped, pyramidal and narrow-faced cores. As noted, further verification is required regarding the date of the emergence of a microblade technology in the Korean Peninsula that is comprised of wedge-shaped microblade cores. However, the archaeological data from the PSHK Peninsula allow us to estimate that such microblade lithic assemblages appeared in Northeast Asia from 26 to 25 cal. ka. It is possible to conclude that the combination of wedge-shaped microblade cores with pressure knapping technique (Mode B), which is the focus of conventional models of microblade technology from an adaptive and behavioural perspective, emerged chronologically corresponding to the onset of the LGM [142].

NAIMA excavated in the PSHK Peninsula include two types of lithic assemblages: those excavated from the Shimaki and Kawanishi-C sites, where only small quantities of microblades were produced from boat-shaped or narrow-faced microblade cores, and those excavated from the lower layers of the Kashiwadai-1 and Pirika-1 sites, where large quantities of microblades were produced out of the standardised wedge-shaped microblade cores. At the Shimaki and Kawanishi-C sites, there are relatively few microblades in the lithic assemblages, and there is no evidence that the pressure knapping technique was used. The second type of lithic assemblage mentioned above indicates that behaviours of making and using microblades systematically and intensively were established. The dating values obtained for the first type of lithic assemblage indicate that they are slightly older than the second type. However, the values for both are quite close, and it is possible that they overlapped in time. We run into difficulties by attempting to provide a simplistic explanation that is rooted only in the migration of human populations for accounting for the diversity that is observed in the reduction processes and knapping techniques that are seen in the NAIMA excavated in the PSHK Peninsula. This raises the necessity of discussing contact between human populations and the cultural changes that may have arisen as a result. A similar perspective may be necessary to understand the diversity of NAIMA in Northern China and on the Korean Peninsula.

6. Conclusion

Although the reliability of the dates needs further verification, recent evidence indicates that NAIMA emerged at 30–28 cal. ka. It is clear that the appearance of NAIMA in Northern China and the Korean Peninsula does not chronologically correspond to the beginning of rapid decline or the absence of sites in North Asia during the LGM. Therefore, previous interpretative frameworks must be re-examined. However, the emergence of NAIMA led to a drastic change in the cultural sequence of Northeast Asia. The commonalities among the techno-typological characteristics between North Asia and Northeast Asia, as confirmed in the lithic assemblage from the Xishantou site, suggest that there were population migrations and/or cultural diffusion occurred. The question is how to understand the evident diversity in the reduction processes and knapping techniques of NAIMA. At the very least, we must recognise that this diversity cannot be explained by a simplistic scenario in which the emergence and spread of NAIMA are solely attributed to the one-time migration of human populations from North Asia.

An additional challenge is to address the methodological question of how to distinguish the evidence of the migrations of human groups from the evidence of cultural transmission between groups. It is apparent that hypotheses inferring multiple locations for the origins of microblade technology within Northeast Asia implicitly rely on convergent evolution. However, there have been few attempts to explain the context in which this occurred until recently. Attention should also be paid to the process of transmitting the knapping techniques of percussion and pressure when there is contact between human groups, considering the difference in knowledge and know-how that constitute the skills of lithic knappers [143, 144].

Acknowledgments

This work was supported by the grant from JSPS KAKENHI (23H00688 and 22 K00990).