Archaeological evidence for initial migration of Neolithic Proto Sino-Tibetan speakers from Yellow River valley to Tibetan Plateau

Significance

Sino-Tibetan is the second largest language family in the world, spoken by more than 1.3 billion people, predominately in China. It originated in the Yellow River region around 8,000 y ago and expanded to the Tibetan Plateau by 6,000–5,000 y ago during the Neolithic Yangshao culture. This study presents the archaeological investigation into the lifeways of Proto Sino-Tibetan speakers, who migrated from the Yellow River to the NW Sichuan highlands. They may have integrated with indigenous hunter-gatherers and adopted broad-spectrum subsistence strategies, consisting of millet farming and local wild resource foraging. They retained important ritual traditions, particularly the alcoholic fermentation method and communal ritual drinking associated with dancing performances, which likely helped maintain their cultural identity and social values.

Abstract

Sino-Tibetan is the second largest language family in the world. Recent linguistic and genetic studies have traced its origin to Neolithic millet farmers in the Yellow River region of China around 8,000 y ago and also suggested that initial divergence among branches of Sino-Tibetan coincided with expansion of the Neolithic Yangshao culture to the west and southwest during the sixth millennium BP. However, archaeological investigations to date have been insufficient to understand the lifeways of these migrant Proto Sino-Tibetan speakers. Here, we present the results of the interdisciplinary research on the material culture and ritual activities related to the initial southwestward migration of Yangshao populations, based on evidence from microfossil remains on ceramics at three sites in Gansu and Sichuan, regional archaeological contexts, and ethnographic accounts of modern Gyalrong Tibetans. The first Yangshao migrants may have integrated with indigenous hunter-gatherers in the NW Sichuan highlands, and adopted broad-spectrum subsistence strategies, consisting of both millet farming and foraging for local wild resources. Meanwhile, the migrants appear to have retained important ritual traditions previously established in their Yellow River homelands. They prepared qu starter with Monascus mold and rice for brewing alcoholic beverages, which may have been consumed in communal drinking festivals associated with the performance of ritual dancing. Such ritual activities, which to some extent have survived in the skorbro-zajiu ceremonies in SW China, may have then played a central role in maintaining and reinforcing cultural identities, social values, and connections with the homelands of the Proto Sino-Tibetan migrants.

Human history includes many layers of migration, one of which is attributable to the expansion of Neolithic farming communities. Neolithic farmers with increasing population densities tended to expand centrifugally from their homelands, introducing their genes, languages, and cultures to the surrounding regions where early farmers had a demographic advantage over contemporary populations of hunters and gatherers (1–3). Sino-Tibetan is the second largest language family in the world, spoken by more than 1.3 billion people, predominately in China. Recent comparative linguistic studies have traced the origin of this language family to the early Neolithic millet farmers in the Yellow River region around 8,000 y ago and suggested that the initial divergence of Sino-Tibetan coincided with the expansion of the Yangshao culture to the west and southwest during the sixth millennium BP (4–6). Supporting the linguistic evidence, genetic studies on ancient Neolithic populations and modern Tibetans demonstrate that the main lineage which contributed to modern population in the Tibetan Plateau originated from Neolithic communities in the Yellow River region (7–9). Despite these research developments on Proto Sino-Tibetan migrations, archaeological investigation on this subject is currently limited.

Archaeological remains of the earliest Neolithic millet-farming communities along the Yellow River valley, which may be related to the Proto Sino-Tibetan speakers, belong to the Dadiwan, Peiligang, Cishan, and Houli cultures (ca. 8000 to 7000 cal. BP), followed by flourishing of the Yangshao and Longshan cultures (ca. 7000 to 4000 cal. BP). The divergence of this language family coincided, in time and space, with expansions of material culture westward to modern Gansu and Qinghai provinces and southwestward to Sichuan province along the eastern edge of the Tibetan Plateau during the middle and late Yangshao culture (ca. 6000 to 5000 cal. BP), accompanied by emergence of the Shilingxia-Majiayao culture (ca. 5900 to 4500 cal. BP) (10, 11) (Fig. 1A). These correlations among archaeological data, linguistic phenomena, and genetic evidence point to a scenario of Neolithic population movements, providing an opportunity to investigate the archaeological remains associated with such migration processes. In this paper, we use the terms migration and migrants to emphasize that the expansion of material assemblages primarily represents the movement of Sino-Tibetan farming communities rather than simply transferal of material culture to indigenous hunting-gathering groups, as demonstrated below. To understand the archaeological aspect of the Proto Sino-Tibetan migration history, a series of systematic investigations of the Neolithic material remains over a very broad region would be required, a task beyond a single article presented here. In this study, therefore, we mainly focus on the material cultures which may represent the first population migrations of Yangshao people from the middle Yellow River to the highlands of NW Sichuan. We first summarize the existing information about the environmental conditions and archaeological background of such migrations and then present our functional analysis of ceramic vessels to investigate how migrants may have adapted to the new environments while maintaining their cultural traditions and identities. We address these questions through the lens of ritual activities by combining multiple lines of evidence from microfossil remains on ceramic vessels, ritual actions, archaeological contexts, and ethnographic accounts.

Fig. 1.

Yangshao culture distribution and comparison of pottery vessels discussed in this study. (A). Circles, I, the Yangshao culture; II, the Majiayao culture. Arrows pointing to the direction of migration. Sites (dots). 1, Dadiwan; 2, Boxi; 3, Haxiu. Inset map, showing the area selected in this study (square in broken line) and the 400-mm and 800-mm isolines of annual precipitation at present (modified from Fig. 5 of ref. 15). (B). Pottery vessels (1–5 from Boxi and Haxiu; 6–9 from Dadiwan). 1, guan jar; 2, jiandiping amphora; 3, painted bo bowl; 4,5, amphora rims; 6, jiandiping amphora; 7, painted hu jar; 8, guan jar; 9, painted bo bowl; 10, 11, amphora rims from BX and DDW, showing heavy worn with vertical striations and organic residues on interiors; 12, amphora rim interior from DDW, showing manufacture traces of horizontal lines with less use-wear, as comparison with 10 and 11 (1–9, representative pottery types from the study region; 10–12, the actual sherds sampled for this study).

We focus on material remains from three Yangshao culture sites in two regions: 1) Dadiwan in Gansu province, representing a community in the Proto Sino-Tibetan homeland of the Wei River valley, a major tributary of the Yellow River; and 2) Boxi in the Min River and Haxiu in the Dadu River, both representing the first Yangshao communities that migrated to the NW Sichuan highlands (Fig. 1A).

Dadiwan of the Yangshao Culture

The Yangshao culture that flourished in the middle Yellow River valley is characterized by sedentary villages, production of painted pottery, domestication of pigs and dogs, and intensive dryland farming with broomcorn millet (Panicum miliaceum) and foxtail millet (Setaria italica) as the predominant crops, supplemented with rice (Oryza sativa) (11, 12). The Yangshao culture was centered in the Wei River valley during its early phase (ca. 7000 to 6000 cal. BP), then expanded to the surrounding regions, particularly to the north and west, during its middle (Miaodigou phase) and late phases (ca. 6000 to 4700 cal. BP), spreading over a very broad region in the middle and upper Yellow River valley. Its western part also evolved into a new variant, known as the Majiayao culture (ca. 5300 to 4500 cal. BP) through a transitional phase, the Shilingxia type (ca. 5900 to 5200 cal. BP), in the upper Yellow River region (10, 11). Meanwhile, material assemblages of middle and late Yangshao as well as Majiayao expanded to include the eastern edge of the Tibetan Plateau in NW Sichuan (13).

The Yangshao and Majiayao culture areas were distributed within the East Asian summer monsoon boundaries, and their western parts were situated along the 400-mm isoline of annual precipitation, which is regarded as a general demarcation historically separating agricultural activity to the southeast from pastoralism to the northwest (14, 15) (Fig. 1A). The Holocene Climatic Optimum, associated with the strong summer monsoon, occurred in North China around 9500–5000 cal. BP. Precipitation increased during the earlier phase, peaked around 7000 cal. BP, and then declined during the later phase, coinciding with the Yangshao culture (7000 to 5000 cal. BP) (16). This phase of dryer conditions may have more severely affected the western part of the Yangshao culture, as suggested by two episodes of severe hydrological recession around 5400 and 5000 cal. BP detected in the Gansu region (17). The Yangshao culture also witnessed growth in population density and social complexity, indicated by an increase of site numbers and of settlement hierarchy cross-regionally (18, 19). This combination of climatic deterioration and population increase formed the backdrop of the Yangshao people’s migration from their homelands.

These changes in settlement patterns are well manifested in the upper Wei River valley, where several large regional centers developed, including the Dadiwan site (Fig. 1A). The site is situated on a hillside near the Qingshui River, a tributary of the Wei River. It was first occupied ca. 7800 BP as a small village, then gradually expanded in size, reaching 50 ha in area during the late Yangshao period. Dadiwan is well known for its big, multiroomed public building (F901; 290 m² in size; 420 m² including affiliated structures) associated with a large open plaza. Pottery vessels of various types were unearthed from the site (Fig. 1B:6–9). Ceramics recovered from Building F901 include a wide range of food vessels, likely used for communal feasting activities (11:193–195, 20). A preliminary study of Dadiwan pottery vessels indicates that jiandiping 尖底瓶 amphorae and hu 壶 jars were related to the production and consumption of fermented beverages (21). In the current study, the Dadiwan vessels were reanalyzed to understand the fermentation techniques.

First Yangshao Culture Sites in NW Sichuan Highlands.

The NW Sichuan highlands are situated on the eastern edge of the Tibetan Plateau, with altitude 3,000–4,000 m asl on average. Its climate conditions vary considerably, depending on different geographical configurations, ranging from cold continental-plateau conditions in the northwest to warm and semihumid conditions in the southeast. Four major river systems (Min, Dadu, Yalong, and Jinsha) flow from north to south, forming natural N-S transportation channels. These river systems, often referred to as the Tibetan-Yi corridor (Zang-yi zoulang), have facilitated human transregional movements since prehistoric times (22, 23).

At least six Upper Paleolithic sites/localities in western Sichuan have been identified, all situated on river terraces, including Fulin and Shizishan in Hanyuan, Huilongwan in Panzhihua, Luhuo in Ganzi, and Jinbaolin and Yanyundong in Beichuan. The associated lithic assemblages resemble the small tool industry and microlithic tradition found in North China, suggesting the existence of N-S-oriented movements of Paleolithic hunter-gatherers prior to the Neolithic migrations. Among these sites, one absolute date (11500 ± 200 BP) has been obtained from Luhuo, and the only excavated site in NW Sichuan is Yanyundong, dating to the late Pleistocene (SI Appendix, Fig. S1) (24, 25). These Paleolithic remains may belong to the first layer of modern humans who occupied the Tibetan Plateau in late Pleistocene, as suggested by genetic studies (7–9).

The first Neolithic migrants occurred in the region around 6,000-5,000 y ago, indicated by the sudden appearance of settlements associated with material assemblages new to this region (pottery, polished stone tools, ash pits, etc.). These migrants appear to have moved to NW Sichuan in multiple waves. The earliest Neolithic deposits appeared at four sites in the upper Min River valley (Boxi, Yingpanshan, Guannaruo, and Jiangweicheng), dating to ca. 6000 cal. BP, and their material remains are comparable with those of the middle Yangshao culture (Miaodigou phase) in the Yellow River valley. The second wave of migration, dating to 5500 to 5000 cal. BP, seems to have been greater in scale, indicated by a broader distribution of sites and larger settlements with thicker material deposits. Their material assemblages, which resemble those of the late Yangshao and Majiayao cultures in the Yellow River region, have been found in the Min and Dadu River regions. In the Min River system, Yingpanshan (5300 to 4600 cal. BP) developed into a large regional center, associated with multiple medium and small settlements. In the Dadu River system, the earliest Neolithic materials appeared at five sites (Haxiu, Konglong, Baishe, Yenongqiujing, and Haneyi), dating to 5500 to 5000 cal. BP (26, 27). Among these sites, Boxi and Haxiu represent the first Neolithic settlements in the Min and Dadu Rivers, respectively (Fig. 1A and SI Appendix, Fig. S1). They are the focus of this study.

Pottery assemblages at Boxi and Haxiu include a small number of painted pottery examples (mainly bo 钵 bowls, pen 盆 basins, and ping 瓶 jars), but the majority are unpainted types. Among many types of cooking, serving, and storage vessels, jiandiping amphorae were found (Fig. 1B:1–5). These vessels closely resemble those of the middle and late Yangshao culture in the Wei River region, including Dadiwan (26, 27). Chemical analysis of ceramics from multiple sites in NW Sichuan suggests that unpainted pottery vessels were made of local clays, while all the painted ones were produced elsewhere, most likely in Gansu (26, 28, 29). The presence of food utensils similar to the Yangshao homelands possibly suggests the practice of a shared culinary tradition, which includes using amphorae for alcohol fermentation (30). The importation of painted pottery also indicates ongoing communications between the migrants and their homelands.

Notably, using the same types of cooking vessels does not mean cooking the same foods. While foxtail millet and broomcorn millet contributed to people’s starchy diet (31, 32), wild animals appear to have been the main source of protein. Faunal remains from Haxiu are all identifiable as wild species, except for a small percentage of domesticated dog (NISP=7, 1.72%; MNI=1, 1.72%) (33). The lithic assemblages from the two sites include considerable numbers of flaked tools (e.g., cutting tools, scrapers, choppers) and microlithics, in addition to polished stone tools with Neolithic characteristics (34, 35). Such faunal and lithic assemblages are very different from those at the contemporary Neolithic sites in the Yellow River region, where the subsistence system was mainly based on millet cultivation and pig husbandry (36, 37). At Dadiwan, the lithic assemblage is predominantly polished stone tools with small percentages of flaked scrapers (6.2 and 3.6% in the middle and late Yangshao, respectively) and without microlithic tools (20).

Taken together, the previous studies show that the first Yangshao culture migrants in NW Sichuan carried out the traditional millet farming, while also engaged significantly in hunting activities. It is unclear, however, whether the migrants also exploited wild plants in the resource-rich highlands and how adaptation to the new environments may have affected their sociocultural traditions.

To address these issues, we analyzed residues on 18 pottery vessels, including amphorae, jars, and bowls from three sites: six from Dadiwan (DDW), eight from Boxi (BX), and four from Haxiu (HX). In addition, we analyzed two sediment samples as controls to test possible post-excavation contaminations: one is from the exterior surface of a jar (DDW18), and the other is from a BX adze (SI Appendix, Fig. S2 and Table S1).

Results

We found large numbers of starch granules, phytoliths, and fungal particles (molds and yeast cells) in the residue samples. Experimental studies show that thin-layer patina residues deposited on cooking vessels represent a mixture of previous cooking events (38). Analysis of such residues on a Yangshao amphora suggests that they are composed of multiple accumulated layers of calcium carbonate and other minerals, in which food particles were trapped and protected, resulting in their long-term survival as microfossil remains (39) (SI Appendix, section 2.1).

Starch Remains.

A total of 2,248 starch grains were found in the residues of 18 pottery samples from three sites (DDW: n=1,105; BX: n=496; and HX: n=105), of which 1,679 (74.7%) were classified into 13 types identifiable taxonomically (Fig. 2) when compared with our modern reference samples. Many starch grains (n=569; 25.3%) lacked diagnostic characteristics or were severely damaged, thus classified as unidentifiable (UNID) (for starch record and identification, see SI Appendix, section 1.1, Fig. S3, and Table S2).

Fig. 2.

Starch types from DDW, BX, and HX. 1, Type I, Panicoideae millet; 2, Type II, Job’s tears; 3, Panicoideae with enzymatic damage; 4,5, Type III, rice; 6, rice, fermented; 7, Type IV, Triticeae; 8, Triticeae with enzymatic damage; 9, Triticeae, fermented; 10, Type V, bean, fermented; 11, Type VI, lily; 12, Type VII, root of snake gourd; 13, Type VIII, ginger; 14, Type IX, eagle fern root; 15, Type X, acorn; 16,17, Type XI, kudzu; 18, Type XII, foxnut, fermented; 19, Type XIII, silverweed; 20, fermented starch, UNID; 21, gelatinized starch mass, UNID (scale, 1–9, 13–19, 10 µm; 10–12, 20, 21, 20 µm. DDW starches, 3,5,10,11,12,13,20; BX starches, 1,2,4,6,7,8,9,15,16,17,18,21; HX starches, 14,19).

Most starch granules show damage characteristics (n=1,567; 69.7% of the total) and can be divided into three types: damage caused by enzymatic digestion (n=549; 24.4% of the total), gelatinization caused by fermentation (n=895; 39.8% of the total), and gelatinization due to cooking (n=123; 5.5% of the total). The morphological alterations due to enzymatic digestion include random pitting, deep channels, broken edges, and central depression (Fig. 2:3,8). Gelatinization caused by low-temperature heating during brewing process is characterized by moderate swelling with a hollowed center, often showing as a birefringent periphery with a dark center (Fig. 2:6,9,10,18,20). The starch damage caused by boiling and steaming shows rather evenly expanded surfaces (Fig. 2:21). These alterations are consistent with reported results from experimental fermentation and cooking (40, 41).

Type I: Panicoideae (n=293; 13% of the total counts; 94.4% of the total ubiquity), including foxtail millet (Setaria italica), broomcorn millet (Panicum miliaceum), and probably small grains from Job’s tears (Coix lacryma-jobi) (Fig. 2:1). They were found at all the three sites, comprising the second most ubiquitous taxon. Such a high level of abundance is consistent with the millet-farming tradition of the Yangshao culture, also conforming to the millet macroremains recovered in NW Sichuan (31, 32).

Type II: Job’s tears (n=38; 1.7% of the total counts; 83.3% of the total ubiquity), occurring at all the three sites (Fig. 2:2). Job’s tears starch has been found at Dadiwan Phase I (ca. 7800 to 7300 cal. BP) (42), and charred Job’s tears has been recovered at the Baodun site in Chengdu, Sichuan, dating to the fifth millennium BP (43). It is unclear whether Job’s tears in our samples was domesticated or of wild form.

Type III: rice (Oryza sativa), found in all residue samples. They mostly appear in a compound form, consisting of multiple small granules, but most granules are blurry due to fermentation (Fig. 2:4–6). We count the percentage of Type III starch based on visible individual granules, which give the most numerous counts and the highest ubiquity in the assemblage (n=785 granules, 192 compounds; 34.9% of the total counts; 100% of the total ubiquity). Rice found in our samples is certainly of domesticated form, as these sites are outside the wild rice distribution.

Type IV: Triticeae (n=306; 13.6% of the total counts; 72.2% of the total ubiquity), found at all the three sites, but more abundant in DDW (n=288) than in BX and HX (n=16, 2). These granules are morphologically consistent with many species under Triticeae tribe, including wheat, barley, and rye, as well as many wild grasses (Fig. 2:7–9). A small number of charred rye has been recovered at HX, while wild Triticeae grasses, such as genera Elymus, Hordeum, and Agropyron, are distributed in western Sichuan (44:table 6–1) and/or Gansu (45). However, it is not possible to further determine the taxonomy of these starch granules.

Type V: bean, probably wild Vigna sp. or Vicia sp. (n=4; 0.2% of the total counts; 22.2% of the total ubiquity), found in DDW and BX samples (Fig. 2:10). Wild Vigna beans grow in western Sichuan today (44:table 6–1), and charred Vigna and Vicia beans have been recovered from Phase III of the Guiyuanqiao site in the Chengdu Plain (ca. 4300 to 4000 cal. BP) (46). Wild pea Vicia sativa L, widely distributed in the middle Yellow River region, is also known to have been commonly used as a famine food in the past (47:338–339).

Type VI: bulb of lily (Lilium spp.), occurred at all the three sites (n=6; 0.3% of the total counts; 22.2% of the total ubiquity) (Fig. 2:11). Many species of lily are distributed in China, including Gansu and Sichuan (48:135–149), and their starches have also been found in pottery vessels from several Neolithic sites along the Wei River valley, including DDW (42, 49).

Type VII: root of snake gourd (Trichosanthes kirilowii), only found in DDW samples (n=14; 0.6% of the total counts; 22.2% of the total ubiquity) (Fig. 2:12). This plant is widely distributed in North China, and its roots were used as food and medicine in antiquity (47:338–339). The starches of this root have also been found in many Neolithic fermentation vessels in the Wei River valley (30:table 1).

Type VIII: ginger root (cf. Zingiber officinale), only found at DDW (n=3; 0.1% of the total counts; 11.1% of the total ubiquity) (Fig. 2:13). Ginger has been used as a spice and medicine since ancient times in China (50). The starch granules resembling ginger have also been found in pottery jars in Phase I of DDW (42), as well as in Neolithic fermentation vessels at other sites in the Wei River valley (30:table 1).

Type IX: Fagaceae acorns, found at all the three sites (n=29; 1.3% of the total counts; 55.6% of the total ubiquity) (Fig. 2:15). Analysis of charcoal remains from DDW suggests that evergreen and deciduous trees, including Quercus aliena, were distributed in surrounding areas at the time of site occupation (20:702). Various evergreen and deciduous oaks grow in western Sichuan today, including the genera of Lithocarpus, Cyclobalanopsis, and Quercus (44:table 9–4), which may have also existed in the past. It is possible that Neolithic people exploited various local acorn species.

Type X: root of eagle fern (Pteridium aquilinum), found at BX and HX (n=129; 5.7% of the total counts; 61.1% of the total ubiquity) (Fig. 2:14). It amounts to the second most numerous taxon in the assemblages from two Sichuan sites, in terms of ubiquity (BX: 100%; HX: 75%). Western Sichuan is reported to have 453 species of fern, including P. aquilinum, which is still widely used as food in China (44:34–46).

Type XI: root of kudzu vine (Pueraria montana), found at BX only (n=17; 0.8% of the total counts; 27.8% of the total ubiquity) (Fig. 2:16,17). China has three endemic species of Pueraria, of which P. montana is widely distributed over the country, including Sichuan. The variant P. montana var. thomsonii (often referred to as P. lobata) is used as a vegetable and for extracting starch (51). Kudzu vine was an important economic plant in ancient China; its vine fibers have been used for making textiles and its roots served as sources of starchy foods and traditional medicine (52). It was also recorded in a 14^th-century document that kudzu vines grew in the valleys of the Wenshan mountains, north of Maoxian, NW Sichuan (47:244–245).

Type XII: root of foxnut (Euryale ferox), found at BX only (n=34; 1.5% of the total counts; 22.2% of the total ubiquity) (Fig. 2:18). Foxnut grows in lakes and ponds and is widely distributed in China (53), including western Sichuan (44:table 6–1).

Type VIII: root of silverweed (Potentilla anserina; juema 蕨麻 in Chinese), found at HX only (n=2; 0.1% of the total counts; 11.1% of the total ubiquity) (Fig. 2:19). Silverweed is an herb under Rosaceae, distributed in many regions of North China; it grows particularly well in the highlands of western China, where people steam or boil its roots for food (54:305, 55). In NW Sichuan, digging silverweed roots in the field is a common task of women and children among pastoralist Qiang people today (56:35). This wild plant is also widely used among Tibetic and Gyalrongic speaking populations. In particular, the Gyalrongic language Japhug has a special verb nɤtsoʁ meaning “collect silverweed” (57:174).

Underground storage organs (USOs; n=25; 1.1% of the total counts; 33.3% of the total ubiquity): They were found at DDW and BX and may come from various tubers or roots, but we are unable to provide precise taxonomy.

The control samples revealed very different starch assemblages. The DDW18 jar has only one Triticeae starch. The BX adze has 29 starches identifiable as Panicoideae, Job’s tears, acorn, fern root, and kudzu, but no evidence of fermentation or cooking was noted, suggesting that this adze may have been used for processing various plants unrelated to fermentation. No rice starch was identified in the controls (SI Appendix, Table S2).

To sum, the presence of fermentation-related damage on starches confirms the function of these vessels as being associated with alcoholic production and consumption. Among the 13 plant taxa, the most abundant ones are cereals, including rice, Panicoideae (mostly millets, but also Job’s tears), and Triticeae, found at all three sites. Millets and rice were domesticated types, likely brought to NW Sichuan from the Yellow River region by the Yangshao migrants, while the domesticity of Job’s tears and Triticeae is unclear. Among the remaining nine plant taxa, acorns and lilies appeared at three sites; snake gourd root and ginger appeared only at DDW; beans were present at DDW and BX; and eagle fern root, kudzu root, foxnut, and silverweed were found at BX and/or HX. Overall, only rice and millets were evidently cultivars, while other plants were either wild or undetermined as to their domesticity.

Phytolith Remains.

A total of 654 phytoliths were recovered from three sites, with the great majority from DDW (DDW: 418; BX: 207; HX: 29) (Fig. 3 and SI Appendix, Table S3). The morphotypes are mainly associated with Poaceae, including epidermal sheets of husk cells from Paniceae and Pooideae grasses, bilobate, polylobate, cross, rondel, bulliform, and elongates. Paniceae husk phytoliths were found only in DDW and BX samples, with η-Type from broomcorn millet (n=77) outnumbering Ω-Type from foxtail millet (n=2). Glumes and leaves of Job’s tears produced great varieties of bilobate, polylobate, cross, and rondel forms, with particularly abundant Variant-1 crosses (quadrilobate forms), which are generally larger than those in millets (<13 µm) (58). Some crosses from BX samples are larger than 15 µm, consistent with Variant-1 type from Job’s tears (Fig. 3:2). Elongate dendriform phytoliths, possibly coming from Triticeae husks, were recovered from DDW (n=13) and BX (n=2). One possible double-peaked phytolith from rice husk was found in a BX sample. Considerable numbers of elongate phytoliths (n=172), mainly from unidentifiable stems and leaves, were recovered. Other morphotypes include opaque perforated platelet (cf. Asteraceae), hair cell (eudicots), and tracheid (xylem), which cannot be further identified.

Fig. 3.

Phytolith from DDW and BX. 1, Cross; 2, Variant 1 cross, Job’s tears; 3, bilobate; 4, polylobate; 5, rondel; 6, elongate echinate silica skeleton; 7, common bulliform; 8, hair cell; 9,10, elongate dendriform; 11, opaque perforated platelets; 12, tracheid; 13, double-peaked rice husk cell phytolith (arrows pointing to peaks, lower peak is blurry); 14, η-Type, broomcorn millet husk; 15, Ω-Type, foxtail millet husk (DDW, 3,4,10,11,12,14,15; BX, 1,2,5,6,7,8,9,13).

The presence of husk phytoliths from millets, Job’s tears, Triticeae, and rice is consistent with starch granules identified to the same taxa in the DDW and BX samples. In HX, however, husk phytoliths were absent, although starches from those cereals were found. In addition, the existence of many noncereal phytolith types suggests that other unidentifiable plants were also involved in the processing and consumption of fermented beverages with those vessels.

Two control samples revealed very few phytoliths, but the BX adze has many bast fibers. These fibers may come from kudzu vines, consistent with the presence of kudzu starch on this tool.

Fungal Remains.

Abundant fungal particles, including molds and yeast cells (n=421), were recovered in all samples from the three sites (for fungal record and identification method, see SI Appendix,  section 1.2, Table S4 and Fig. S4). The most numerous elements are cleistothecia, consistent with genus Monascus mold (n=330; 52.2% of the total; 100% ubiquity). Monascus is divided into more than a dozen species, which are mainly found in oriental food. This fungus produces a bright red color and has been used as a fermentation starter, food pigment, and an ingredient in traditional Chinese medicine. Monascus is known to have been included in the red rice qu starter used for brewing traditional rice-based red beer, often referred to as red rice wine or red wine (59:166–169, 60:192–203). In our ancient samples, Monascus cleistothecia exhibited characteristics of different growth stages: some connecting with hyphae in an early developmental phase, some showing asci and ascospores in mature phases, and some ruptured with most ascospores being released in a final phase. Their morphologies (Fig. 4:1–4,9) match very well with published information and Monascus samples in our reference database (SI Appendix, Fig. S4:1–3,9).

Fig. 4.

Fungal elements from DDW, BX, and HX (1–14) and modern yeasts (15, 16). 1, Monascus ascogenous cleistothecia, initiation of branched sterile investing hyphae around the ascogonium; 2, Monascus immature cleistothecia, showing elongate hyphae on the cleistothecial wall; 3, Monascus mature cleistothecia; 4, Monascus, ruptured cleistothecium releasing ascospores; 5, Aspergillus vesicle connected with phialide and conidia; 6, Rhizopus, sporangiophore connected with columella and collarette; 7, Penicillin, conidiophore/branch connected with phialides and conidia; 8, possible Rhizopus sporangiophores opposite to rhizoids; 9, septate hypha, possibly from Monascus; 10, sporangia (pointed by arrows) connected with hypha, possibly Rhizopus or Mucor; 11, yeast cell from DDW, comparable with 16; 12, yeast cell from DDW, comparable with 15; 13, 14, yeast cells in budding process from HX, comparable with 16; 15, modern yeast Pichia kudriavzevii (elongate); 16, modern yeast Saccharomyces cerevisiae.

Small numbers of other molds, including genera of Aspergillus (n=1), Rhizopus (n=2), and Penicillium (n=1), were found in DDW samples (Fig. 4:5–7). In Chinese traditional qu starters, Aspergillus and Rhizopus are among the most commonly used functional molds (59, 61), whereas Penicillium is considered to be an undesirable contaminant (62). Among fungal elements which are classified as unidentifiable taxonomically (UNID), some are likely Rhizopus or Mucor (Fig. 4:10). These two molds share some similarities in morphology but can be specifically differentiated based on the presence (in Rhizopus) or absence (in Mucor) of rhizoids (63). However, no relevant fungal part was found in these cases to facilitate this identification.

Fungal hyphae and/or mycelia (n=158) were present in all the samples. Some are septate, resembling those from Monascus (Fig. 4:9), and others are aseptate or rarely septate, like those from Aspergillus, Rhizopus, or Mucor (Fig. 4:8), supporting the identification of other elements from these molds. In the control samples, only a few unidentifiable hyphae were recovered.

Yeast cells (n=161) were found in vessels from all the three sites. Two morphotypes were present. One type is elongate oval, measuring 9.23–11.2 µm in size, morphologically consistent with Pichia kudriavzevii in our reference database. The other type is round or oval, measuring 3.69–11.12 µm in size, consistent in form with those of Saccharomyces cerevisiae. Pichia spp. and particularly S. cerevisiae are commonly found in qu starters in China (61, 62), but we are unable to identify the taxonomy of the yeast cells in our samples based on morphology alone (Fig. 4:11–14, compared with 15,16).

The presence of abundant fermentation-related molds and yeast cells in the samples further confirms the vessels’ function as associated with alcoholic beverages. The fermentation agent was most likely the qu starter, which contained molds predominantly from Monascus at all the three sites, with much smaller amounts of functional molds from Rhizopus and Aspergillus at DDW.

Discussion

The microfossil remains recovered from pottery vessels provide new insights into the subsistence and ritual activities of Proto Sino-Tibetans of the Yangshao culture, who migrated from the Yellow River valley to NW Sichuan highlands. We now discuss this transition from two aspects: the adaptation to new environments and the maintenance of traditional ritual practices. By integrating the functionality of ceramics with broader material and cultural contexts, we further explore the mechanisms which may have helped the migrants maintain cultural identities and social connections with their homelands.

Subsistence Strategies of Both Farming and Foraging: Continuity and Adaptation.

The starch and phytolith remains from the vessels examined indicate that people exploited diverse plant resources, which were used to make fermented beverages and very possibly also for daily food. The 13 plant taxa can be classified into three groups, in terms of their presence, as follows. 1) Domesticated millets and rice, ubiquitous in high percentages, appear to be the core ingredients for alcohol brewing at all the three sites. 2) Some widely distributed plants were found in both regions, including Triticeae, Job’s tears, acorn, lily, and bean, some of which were likely wild. 3) Several plants appear to have been exclusively used at one or two sites: snake gourd root and ginger were only found at DDW; eagle fern root at BX and HX, kudzu root and foxnut only at BX, and silverweed only at HX (SI Appendix, Fig. S5). These patterns show that the Yangshao people in the Wei River homelands practiced a mixed farming–foraging subsistence economy and used mainly domesticated cereals supplemented with various wild plants for subsistence and alcohol brewing. When moving to NW Sichuan, the Yangshao migrants maintained the mixed farming–foraging strategies, by exploiting wild plant resources available in the highland environments, particularly the roots of eagle fern, kudzu, and silverweed.

The adaptation to the foraging of local wild plants by the Yangshao communities in NW Sichuan is an important issue. Many types of flaked tools, including microblades, were found at BX and HX (64, 65), but were absent at DDW and other Yangshao sites in the Wei River valley. These flaked tools, at least partially, may represent the material remains of local hunter-gatherers who were the first layer of Upper Paleolithic populations on the Plateau. Genetic studies suggest that the peopling of the Tibetan Plateau involved multiple waves of admixture among populations, including not only Neolithic farmers from the Yellow River region, but also a small portion of more ancient peoples who arrived during the late Pleistocene (7–9). It is possible, therefore, that the first Yangshao migrants may have integrated with indigenous hunter-gatherers and adopted local foraging skills.

Brewing Alcoholic Beverages for Ritual Activities: Maintaining Cultural Traditions.

Linguistically, a cognate set for “alcoholic beverages” can be traced back to Proto Sino-Tibetan, based on Sino-Tibetan Etymological Dictionary and Thesaurus (STEDT) (66), suggesting that fermentation technology has a very deep history in the Yellow River region. Supporting the linguistic data, microfossil analysis of residues on Neolithic pottery vessels (mainly globular jars and amphorae; ca. 9000 to 5000 cal. BP) in North China has demonstrated that they were used to brew alcoholic beverages. The fermentation ingredients include multiple cereals (such as millet and rice) and various tubers; the brewing methods may have included the use of honey and fruits (67), malts, and qu starter (30, 68) as saccharification agents. At least four genera of molds (Aspergillus, Rhizopus, Monascus, and Mucor) for making the qu starters have been identified in the Yangshao fermentation vessels (30). The current study reveals that the material remains related to alcohol production and consumption among the three sites are remarkably similar and are also consistent with those from other Yangshao culture settlements.

The first similarity is the brewing method, in that qu starter may have been prepared mainly with Monascus mold and rice, while fermentation ingredients include multiple types of grains and tubers. Rice and Monascus have traditionally been used together for making hongjiuqu (red beer qu starter), a brewing method that most likely originated in parts of southern China, such as the Yangzi River valley (59:166–169, 60:192–203), where rice was first domesticated.

Based on previous studies, rice was used for brewing alcoholic beverages at the Lingkou site (Shaanxi province) in the lower Wei River region, dating to ca. 7800 cal. BP (68). Rice has also been found at Nanzuo in Qingyang (carbonized seeds) and Xishanping in Tianshui (phytoliths), both dating to ca. 5000 BP, in the upper Wei River region (Gansu province) (69, 70). In Sichuan, phytoliths of rice and millets have been recovered from Guijiabao in Yanyuan, probably coming from the north through the Tibetan-Yi Corridor, dating to no later than 5000 cal. BP (71). The rice microfossil remains we found at the three sites account for the earliest examples of this crop in the upper Wei River valley and the Tibetan-Yi Corridor.

Rice starch granules are small and difficult to identify due to gelatinization caused by steaming and fermentation during the brewing process. This situation may result in rice starches being overlooked during starch analysis. Also, identifying fungal remains in archaeological materials is a new and ongoing effort in the field of microfossil analysis, and we have only recently recognized the presence of Monascus molds in residue samples. We have recently reexamined some residue samples from the Lingkou site in Shaanxi (ca. 7800 cal. BP), which were reported in a previous study (68), and have confirmed the coexistence of rice and Monascus molds. Our latest publications demonstrate that fermentation vessels containing both rice and Monascus occurred by the sixth millennium BP at several sites in northern China (72–74). Thus, it is likely that this brewing method was introduced to northern China during the early Neolithic period and became widespread later through the Yellow River region.

Preparing qu with rice and Monascus for alcohol fermentation appears to have become a core cultural tradition consistently practiced by the Yangshao populations wherever they moved, including to NW Sichuan. However, it is unclear whether rice was produced at the three sites examined here, since no charred rice remains have been reported and rice husk phytoliths are rare in residue samples. This situation may be explained by several possible scenarios, which may not be mutually exclusive: 1) Rice was thoroughly dehusked before being used for fermentation; 2) rice was produced locally or brought to the sites in small quantities for special purposes (e.g., fermentation) and rarely survived in charred condition; and/or 3) small quantities of rice–Monascus-based qu starter compounds were brought to the sites from elsewhere. In any event, rice was unlikely a major staple food in this part of China, but was a “luxury food” as defined by Veen (75), mainly used for alcohol fermentation. Importantly, the consistent materiality of the rice–Monascus combination in alcohol production may have played a crucial role in maintaining the authenticity of ritual feasting traditions among Yangshao communities.

Cultural continuity is also manifested in the alcohol-related vessels. Amphorae (conical-based or flat-based) were used not only as fermenters, as revealed by the residue analysis, but also as drinking vessels. Many Yangshao amphorae are damaged or heavily worn on their rims, with some showing vertical striations on the interior walls of the rim and neck (30). Such use-wear traces are also observed on amphora sherds from DDW, BX, and HX, which show sharp contrast to a rim sherd with original manufacture traces (Fig. 1:10–12). Based on our experimental study, similar striations can be created by repeatedly rubbing a reed stem in a unidirectional motion against a sherd (Fig. 5:9–11), suggesting that such use-wear patterns likely resulted from using reed or bamboo straws for drinking from the vessels. Communal drinking through straws from large amphorae (up to 70 to 90 cm high) appears to have been a long-lasting tradition, as an essential part of feasting events in the Yangshao culture (30).

Fig. 5.

Archaeological and ethnographic analogies related to communal dancing and drinking rituals. 1, Large public building F901 at DDW (76:Fig. 2) and its reconstruction (1a) (77:Fig. 5); 2, line drawing of DDW house floor (F411) with dancing scene, and the original photo (2a) (20:fig. 288, color plate III); 3, opening ceremony of skorbro ceremony, showing a Gyalrong community leader offering alcohol to deities 78; 4, 5, a group of Gyalrong women with zajiu drinking and a group of Gyalrong men performing skorbro dance (79:54); 6, a large group of Gyalrong people performing skorbro dance, surrounding a zajiu jar, showing counterclockwise movement 78; 7, 8, Majiayao pottery basins with dancing scene from Shangsunjia and Zongri, Qinghai province (80:plate I, 81:plate I); 9, a Yangshao culture amphora from Zhugeshuiku in Luoyang; 10, vertical striations on the interior wall of the Zhugeshuiku amphora; 11, striations created by rubbing a reed stem against a sherd in an experimental study.

People worldwide have practiced such a communal drinking method since Neolithic times 82–84. In China, drinking alcohol in groups through straws, referred to as zajiu 咂酒 in Chinese, was first documented in Huayang Guo Zhi (Chronicles of Huayang; AD 348–354), has been described in many later texts, and still exists among many Sino-Tibetan ethnic groups in southwest China today, such as Qiang, Tibetan, Miao, Gelao, Tu, and Yugu 85. Zajiu plays a pivotal role in the skorbro (guozhuang 锅庄) dancing ceremony in southwest China, in which dozens to hundreds of people may participate. They hold hands while singing and dancing in a circle, often with the zajiu jar placed in the center to serve the participants. The skorbro-zajiu ceremonies are conducted on various occasions, ranging from seasonal festivities to life cycle celebrations, and their primary effect appears to emphasize sharing, so as to encourage and reinforce cultural identity, group solidarity, and various social connections 86–89. The alcoholic beverages used for zajiu are fermented with multiple grains, and xiaoqu (small qu starter, made of rice) is used as a fermentation agent today, but wild grasses were added to the qu starter in the past (89:127, 90). Such a fermentation technique largely resembles that of the Yangshao culture. Notably, in both Yangshao and modern cases, the fermenters are also used as drinking vessels.

The similarities in ritual drinking practice between the Yangshao people and modern Sino-Tibetans in southwest China are intriguing. The Yangshao communal drinking may have also been associated with dancing, like the skorbro ceremony today, as discussed below.

Archaeological and Ethnographical Analogies in Settlement Pattern and Dancing–Drinking Rituals.

Skorbro means “circle dance” in Tibetan. It also refers to a hearth associated with cooking pots and extends to people dancing in a circle around the hearth. The skorbro-zajiu ceremony can take place inside a residential house, a public building, or in an open plaza, suggesting that the ritual performance is facilitated by certain built environments 89. Some elements of such a ceremony, observable in the Gyalrong (Rgyalrong, Jiarong 嘉绒) Tibetan groups in NW Sichuan, find parallels in aspects of the Yangshao culture remains, such as settlement pattern, ritual space, and dancing–drinking styles.

Gyalrong Tibetans reside in the region approximately overlapping with the distribution of Yangshao sites in NW Sichuan highlands. They build settlements in various landscapes, and one type of settlement layout on river valleys and gentle hillside slopes exhibits a centripetal arrangement 91. In such villages, a plaza associated with public building(s) for collective ritual or religious activities, including skorbro and zajiu, is normally situated in the central location or the highest spot, surrounded by residential dwellings 79, 91, 92 (SI Appendix, Fig. S6:4,5). The public buildings may include a porch-like front structure, providing a space for an audience to observe the ceremony (Fig. 5:3). Similarly, typical Yangshao culture settlements are characterized by a centripetal layout, in which all the houses, including large public buildings, were arranged with doors facing the central plaza, exemplified by the Jiangzhai site in the Wei River valley 93. At DDW, the public building F901 affiliated with a porch-like structure (Fig. 5:1) and an open plaza was built on the highest location of the settlement on a hillside landscape (SI Appendix, Fig. S6:1, 3).

Among the Gyalrong Tibetan groups, the authentic orientation of the dancing movement is counterclockwise, which may have derived from some concepts in the ancient pre-Buddhist Bon religion embedded in the Gyalrong belief system (89:180–200) (Fig. 5:4–6). A group of human figures (two complete and two partially remaining) in a dancing formation was painted with black pigment on the floor around the hearth in a house (F411) at DDW; the original number of human figures in this scene is likely to have been greater, but later diminished by damage to the floor surface (Fig. 5:2) (20). Also, pottery basins painted with dancing scenes, in which assembled people hold hands with one another, have been found at several Majiayao culture sites 94, and the dancing formation resembles the skorbro (Fig. 5:7,8). Notably, the dancers’ heads on the DDW house floor and on the Majiayao pottery basin from Shangsunjia in Qinghai province 80 appear facing right (Fig. 5:2,7), indicating that the direction of the dancing movement was counterclockwise (89:189). Circle dancing scenes on pottery vessels have been found in Neolithic and Chalcolithic cultures in the Near East and southeast Europe; such a movement enhances the feeling of unity and elation 95. While circle dancing is not unique to the Sino-Tibetan case, those dancing images found in regions outside China do not resemble the dancing styles consistently expressed in skorbro, and on the DDW floor painting and Majiayao painted pottery. No group dancing scene has been found in the contemporaneous Neolithic cultures in other parts of China (e.g., Hongshan, Dawenkou, Hemudu, and Qujialing).

The skorbro dance emphasizes vigorous movements of legs and feet, such as kicking, stepping, trampling, and jumping. Men also tend to use more upper body movements without holding hands (Fig. 5:5). Such dances often result in clouds of dust rising in the air when reaching a climax in an open field (89:10–16, 80). The dancing scenes on the DDW house floor show individuals dancing with crossed legs and without holding hands, comparable with the skorbro male dancers (Fig. 5:2; compared with Fig. 5:5). If the dance was held inside a building, a hard and clean floor surface would have been beneficial to facilitate such activities. The public buildings in the Yangshao culture were normally constructed with well-cemented floors, and some had a hearth in the center (Fig. 5:1). At the late Yangshao site of Huizui in Henan province, for example, 11 layers of the floor in a large building were sequentially constructed through multiple episodes of repair and rebuilding. Micromorphological analysis suggests that the full sequence consists of superimposed tufa slabs and well-prepared, hard adobe surfaces, forming strong and solid floor surfaces 96 (SI Appendix, Fig. S6:2). These conditions would seem to facilitate fulfillment of the culturally determined need for frequent group dancing. Microfossil remains (starch and phytoliths) of fermented beverages have been recovered from the adobe surfaces of this floor sequence, indicating that drinking was part of the activities conducted there 97. At DDW, a large public building (F901) with a well-cemented floor and a large central hearth was associated with an open plaza having multiple layers of trampled soils 20, 76, suggesting intensive communal gathering activities (Fig. 5:1). This plaza–public building complex was located on the highest area of the entire DDW settlement (SI Appendix, Fig. S6:3).

The current archaeological evidence also indicates that this centripetal settlement design, focusing on a plaza–public building complex, may have been introduced by the Proto Sino-Tibetan migrants to NW Sichuan and continued there for thousands of years. At Yingpanshan (5300 to 4600 cal. BP), a site near Boxi, an open plaza with trampled surface soil has been identified (28). Excavations at Shidaqiu in Markang, near Haxiu, have revealed a Han dynasty settlement (ca. 200 BC to 200 AD), composed of a central plaza associated with a large public building 98. Such a built environment for facilitating communal dancing and drinking appears to have been a long-lasting tradition persisted until today in NW Sichuan.

Bodily Social Memory as an Essential Aspect of Social Memory.

If the skorbro-zajiu ceremonies practiced by Sino-Tibetan groups in southwest China originated among their prehistorical forbears in the Yellow River region, how and why could such ancient ritual activities have persisted for thousands of years? We suggest that this tradition may have been transmitted through bodily social (collective) memory.

Social memories are shared representations of a group’s past, based on its common identity. Such memories are formed in the context of human interactions with other humans or with cultural artifacts and inhere in the definition, maintenance, and mobilization of social identities 99. Social memory is likely to be found in commemorative ceremonies, particularly collective rituals, which engage bodily movement. Collective rituals are effective for recalling and reenacting a definitive event, through repetitive reactivation of cognitive representation 100. By performing the same gestures, adopting the same postures, and singing the same songs in unison, bodily collective rituals lead to an important social sharing of emotions and generate feelings of “identity fusion.” This experience then revives the common identity and the beliefs associated with it 101.

Ethnic groups in NW Sichuan have deep ancestral roots linguistically and culturally, which can be traced to the north. The Gyalrong people, for example, speak a group of languages retaining many of the Proto Sino-Tibetan phonetic and morphologic forms, including the word for grains of millet or rice 102, 103. The Gyalrong also preserve some elements of ancient pre-Buddhist Bon religion, such as veneration of natural deities and practice of shamanism (104:84–88, 105). During the skorbro ceremony, alcohol was first offered by the community leader to various deities/gods and ancestors as a sacrificial item, and then consumed by the participants in an order based on age group and gender, from senior to joiner and from male to female (Fig. 5:4–6) (89:126–129, 78). In this way, zajiu was shared by gods and humans. The containers used for drinking zajiu are considered part of the ritual paraphernalia. In one case, the host of a wedding skorbro ceremony borrowed an ancient vessel (which was regarded as more authentic) from relatives to fulfill this obligation (89:77–104). Such an age–gender-based ranking system and an attitude of archaicism toward zajiu vessels may have derived from an ancient ritual tradition. Through formalized acts in ritual performance and use of ritual paraphernalia, conducted in the conventional built environment, the skorbro ceremony plays a pivotal role in connecting humans with gods, humans with humans, and present with past; it also helps reinforce traditional social configurations and maintain cultural identities and unity. This practice may explain why the first Yangshao settlers in NW Sichuan obtained painted pottery vessels from Gansu: these ritual paraphernalia may have been highly valued socially and emotionally for their authentic origins from the homelands of Sino-Tibetan migrants.

Conclusion

Adopting a focus on materiality in ritual activities, supported by multiple lines of evidence from microfossil remains, archaeological contexts, settlement patterns, and ethnographic accounts, we have elaborated possible features in the process of initial migrations by Proto Sino-Tibetans from the Yellow River valley to NW Sichuan highlands during the sixth millennium BP. The southwestward dispersal of the Yangshao farmers appears to have been associated with increased population pressure coupled with climatic fluctuations toward the end of the Holocene Climate Optimum in North China. The migrants brought farming techniques (millets and possibly rice) with them, and they exploited diverse wild resources in the NW Sichuan highlands. They may have integrated with indigenous hunter-gatherers and adopted local foraging technologies, while retained their traditional cultural practices, such as making fermented alcoholic beverages for ritual activities. The persistence of cultural tradition is characterized by 1) preparing the qu starter with rice and Monascus mold; 2) brewing alcoholic beverages with multiple grains, tubers, and nuts; 3) using amphorae both as brewing vessels and as drinking containers; and 4) conducting group dancing performances together with communal drinking through straws (reed or bamboo) in a central plaza and/or associated public buildings. These ritual activities, transmitted through bodily social memory, may have played a central role in the Neolithic migrants maintaining and reinforcing their cultural identities, social values, belief systems, and connections with the homelands in the Yellow River region, after they expanded to the eastern edge of the Tibetan Plateau. Some of these ritual features appear to have survived in the skorbro-zajiu ceremonies practiced among many Sino-Tibetan ethnic groups in SW China today. Further research is needed to investigate the genetic relationships between Neolithic peoples and modern populations in the Yellow River and the NW Sichuan highlands, as well as the historical development of these ritual traditions. Such data may hold the key to understanding the genetic, sociocultural, and spiritual dimensions of the Proto Sino-Tibetan peoples.

Materials and Methods

Sample processing involved two procedures: 1) EDTA (ethylenediaminetetraacetic acid; 0.1%) dispersion to release microparticles (starch, phytoliths, fungi, and fibers) from small sediment microaggregates; and 2) SPT heavy liquid (sodium polytungstate, density 2.35) separation to extract microbotanical remains. Extracts were mounted in a 1:1 (vol:vol) solution of glycerol and distilled water on glass slides and scanned under a Zeiss Axio Scope A1 fitted with polarizing filters and differential interference contrast (DIC) optics, at 200× and 400× for starch, phytoliths, fungi, and fibers. Photographs were taken using a Zeiss Axiocam HRc3 digital camera and Zeiss Axiovision software version 4.9.

(See SI Appendix, section 2 for more discussion).

Supplementary Material

Appendix 01 (PDF)

Data, Materials, and Software Availability

All study data are included in the article and/or SI Appendix.