The Impacts of Climate Change on the Neolithic Cultures of Gansu-Qinghai Region During the Late Holocene Megathermal

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The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region during the late Holocene Megathermal

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Available from: Hou Guangliang Retrieved on: 02 December 2015 J. Geogr. Sci. 2010, 20(3): 417-430 DOI: 10.1007/s11442-010-0417-1

The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region during the late Holocene Megathermal

LIU Fenggui1,2,3, ZHANG Yili3, FENG Zhaodong4, HOU Guangliang2, ZHOU Qiang2, ZHANG Haifeng2

1. School of Geography, Beijing Normal University, Beijing 100875, China; 2. School of Life and Geographic Science, Qinghai Normal University, Xining 810008, China; 3. Institute of Geographic Sciences and Natural Resources Research, CAS, Beijing 100101, China; 4. Key Laboratory of Western China's Environmental Systems (Ministry of Education), Lanzhou University, Lanzhou 730000, China

Abstract: The Holocene Megathermal is divided into early, middle and late periods, each having different impacts on the Neolithic cultures due to their different climate changing trends. This study is based on a comparative analysis of the environmental evolution information recorded in the Qinghai Lake, the western edge of the Loess Plateau and Zoige and the spatial distribution of Neolithic sites of the Gansu-Qinghai region. Results show that the early and middle periods towards warm and humid promoted the development of Neolithic cultures with agriculture as the main sector in the Gansu-Qinghai region, furthermore a heyday of Yang- shao Culture prosperity emerged. The Holocene entered the late period after the cold climate event at 5.9 ka BP in the Gansu-Qinghai region. Later the climate began to turn cold. How- ever, at the 5.8–4.2 ka BP a relatively stable warm and humid climate created the conditions for the development of Majiayao Culture of the Neolithic Age in this region, thus the distribution of its cultural heritage sites expanded towards high altitudes and high latitudes. From 4.2 ka BP onwards, the climate became cold and dry, which had a significant influence on the Neolithic cultures of the Gansu-Qinghai region, leading to a dramatic change in the cultural characters and spatial distribution of Qijia Culture around 4.2 ka BP. After a nearly 300 years of cold and dry period, the unified Neolithic farming culture completely collapsed. Afterwards an industrial division of animal husbandry and farming and regional multiple cultures formed, and ultimately led to the end of primitive society and the starting of a civilized society.

Keywords: Gansu-Qinghai region; Neolithic cultures; climate change

1 Introduction The impact of environmental change on archaeological cultures is a major aspect in the research into the past man-land relationship. During the late period of Holocene Megathermal

Received: 2009-08-10 Accepted: 2009-11-03 Foundation: National Natural Science Foundation of China, No.40771211; No.40261003; National Key Technology Re- search and Development Program, No.2007BAC03A11 Author: Liu Fenggui (1966–), Professor, specialized in regional geography related to the Tibetan Plateau. E-mail: [email protected]

www.scichina.com www.springerlink.com 418 Journal of Geographical Sciences

(Shi, 1992; Shi et al., 1992; Wang and Gong, 2000), a dramatic climate change produced far-reaching influence on the turning of Chinese Neolithic culture. A large number of research data show that the turning point of Chinese Neolithic culture was closely related to the 4.2 ka BP cold and dry event during the Holocene Megathermal (data used in this article are the corrected age) (Huang et al., 1991; Zhou et al., 1992; Mo et al., 1996; Zhu et al., 1996; Zhang et al., 1997; Fang and Sun, 1998; Wu and Liu, 2001; An et al., 2003; Liu et al., 2005). The Tibetan Plateau and northern China's farming-pastoral zone are considered to be sensitive to climate change (Zhang et al., 1997; Zheng and Yao, 2004), and therefore the study on the impacts of climate change events of these regions on Neolithic human activities have important theoretical and practical significances. The Gansu-Qinghai region, as a transitional zone between the Tibetan Plateau and the Loess Plateau and with an altitude of 1000–3500 m, is a sensitive and vulnerable area to the environmental changes in China, where environmental change information has been recorded in the rich lake sediments, loess accumula- tions and peat sediments. Besides, in the region studies on Neolithic archaeological culture are more comprehensive, Neolithic cultures are well developed and preserved with integral sequences, and the Neolithic cultural sites are densely distributed (Xie, 2002), which dominated development of early Chinese civilization (Yan, 1997). In the late Holocene Megathermal, affected by dramatic climate change, the Neolithic cultures had an important turning point (Mo et al., 1996; An et al., 2003; Hou and Liu, 2004), that is, animal husbandry and farming industries separated into the two major social divisions of labor, thus a unified farming culture went from rise to decline, and then disappeared.

2 Climate changes of the Gansu-Qinghai region during Holocene Megathermal Holocene Megathermal refers to the warmest interglacial period after the last glacial period. It occurred at 8.5–3.0 ka BP in China (Shi, 1992; Shi et al., 1992). During the early period of 8.5–7.2 ka BP, the earth's climate fluctuated and the average global temperature became warmer. Temperature and precipitation presented a clear upward trend in the frequent fluctuations. In this period, agriculture-based Neolithic cultures developed rapidly. During the middle period of 7.2–6.0 ka BP, temperature and precipitation reached their maximum val- ues, and due to lush vegetation, the Yangshao Culture reached a peak in Neolithic prosperity. During the late period of 5.9–4 ka BP, the earth’s climate fluctuated with a downward trend of temperature and precipitation, of which 5–4.2 ka BP was a relatively stable stage during which the number of cultural sites soared. The end of the Holocene Megathermal at around 4.2 ka BP had a profound impact on the Chinese Neolithic cultures due to extreme climate instability. Environmental information for lake cores of Qinghai Lake in northeast of the Tibetan Plateau (3195 m asl) (Liu et al., 2002; Figure 1a), Sujiawan loess section of the western edge of the Loess Plateau (1950 m asl) (Feng et al., 2004, Figure 1b), and Zoige Hongyuan peat core section on the south-east edge of the Qinghai–Tibet Plateau (3466 m asl) (Hong et al., 2003; Figure 1c) can be extracted to better reflect the Gansu-Qinghai region (to be dis- cussed in this paper) in the Holocene climate and environmental changes. LIU Fenggui et al.: The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region 419

Figure 1 Climate change of the Gansu-Qinghai region recorded in different environments during late Holocene Megathermal (after Liu Xingqi et al., 2002; Feng Zhaodong et al., 2004; Hong Yetang et al., 2003)

The past records from the above three regions (Figure 1a-c) show that, since 10 ka BP, spruce, pine and other conifer pollen levels have significantly increased, while herbs pollen reduced. The entire region shifts from grasslands to forest or forest-grassland (Du et al., 1989; Kong et al., 1990; Liu et al., 2002; 2003; Shen et al., 2004; Feng et al., 2004; Sun et al., 2008; Zhou et al., 2001; Liu et al., 1994, 1995). Up to the early period of Holocene Megathermal, mixed coniferous and broad-leaved forests were well developed in the Qing- hai Lake region, with Betula a small amount of thermophilic Ulmus. Pinus, fir, spruce and iron Suginami could be found in the western edge of the Loess Plateau, with mixed coniferous and broad-leaved forests composed of Betula, Juglans, Ulmus, and Gramineae, As- teraceae, Artemisia (Sun et al., 2008). Spruce and fir were mainly distributed in Zoige region, with mixed coniferous and broad-leaved forests consisting of oak, chestnut and roses, etc. (Wang et al., 1996). Seen from plants and sediments, the climate presented a warming trend in spite of frequent fluctuations of temperature and precipitation (Zhang et al., 1994; Chen et al., 1990; Feng et al., 2004; Wang et al., 1993). The salinity of the Qinghai Lake reached a low level around 6.3 ka BP (Zhang et al., 1994), and the lake surface was 40 m higher compared to the present (Wang and Wang, 1992). In this period, Picea purpurea and elm were found on the lakeshore, and a large amount of wet herbs in Sujiawan section. Be- sides the pollen concentrations of trees and shrubs went up to 80% of the peak (Sun et al., 2008). Both the Hongyuan’s peat gradation and total organic carbon content were the high-

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est (Zhou et al., 2001). It can be inferred that the annual mean temperature was about 3℃ higher and the precipitation was increased by 240–300 mm compared to the modern times (Shi, 1992), which showed a heyday of the Holocene Megathermal. Temperature and precipitation began a turning point after 5.9 ka BP cooling event. The sediments of the Qinghai Lake have more particles with a grain size of <4 μm, while particles of > 64 μm tend to be stabilized (Shen et al., 2004 ), indicating that precipitation tended to decrease, that larger amount of Artemisia increased significantly in lake area, and that pine and other tree pollen concentrations decreased significantly. Meanwhile, the plants shifted from forest to forest-grassland (Liu et al., 2002). Conifers, grasses, and Artemisia pollen in Sujiawan section also increased significantly, shifting from the forest-grassland to grassland (Feng et al., 2004). In Zoige region at the 5.6 ka BP the gray-scale and total organic carbon content began to reduce (Zhou et al., 2001), the δ13C value of peat fiber ele- ments increased, decomposition of plant debris decreased, and humification degree reduced (Hong et al., 2001; 2003). At the same time, fir disappeared from the sunny slope, spruce began to migrate towards northern slope, and the forest area reduced and evolved into island forests (Wang et al., 1996). The climate tended to be cool and dry. Around 4.2 ka BP there was a sudden distinct drop in the total pollen concentrations in sediments of the Qinghai Lake. Woody plants disappeared, and herbaceous pollen was significantly reduced, while cold-dry Thalictrum, ephedra and others increased, and Artemisia pollen resistant to cold and drought increased to 70% (Liu et al., 2002). Lake water level dropped with a sharp decline in carbonate content (Zhang et al., 1994). The ecological environment rapidly evolved into Artemisia dominated grassland landscape (Liu et al., 2002). In Sujiawan region, broad-leaved trees pollen ingredients reduced to 20%, terrestrial herbs, dominated with Chenopodium and Artemisia reached 80%, leading to the end of development of wetlands-swamp layer (Feng et al., 2006), grassland and desert steppe were also alternating (Sun et al., 2008). In Zoige region, peat humification and pollen fell to the lowest level (Hong et al., 2003). Sub-alpine meadow and shrub meadow areas rapidly expanded. Swamps retreated from wide gully and foothills to the lowlands. Spruce forest disappeared on the gentle sunny slope (Wang et al., 1996). All the above information indicates that the climate had a major turning point in the Gansu-Qinghai region, before that the hottest monthly average temperature was 1–2℃ higher than the present, and the coldest monthly average temperature was 8.7–11.7℃ higher than the present (Du et al., 1989). Around 4.2 ka BP the climate was similar in the Gansu-Qinghai region compared to the present conditions. Therefore, it was likely that the cooling events marked the approaching end of the Holocene Megathermal. The cooling event was consistent with the North Atlantic cooling (Bond et al., 1997), glacial advancement in the Alps (Perry and Hsu et al., 2000), extreme drought events in North Africa (Petit-Maire et al., 1983; Petit-Maire and Riser, 1983; Claussen et al., 1999); the dry and cold events in Indian River Basin, West Asia, West Af- rica, Mexico and other regions (Gasse and Campo, 1994; Siroeko et al., 1996); cultural col- lapses in Mesopotamia region (Weiss et al., 1993; Cullen et al., 2000), as well as cooling events occurring in China's Yellow River Basin, Yangtze River Basin, Xinjiang, western Tibetan Plateau, Northeast region and Lingnan region (south of Manling Mountains) (Liu et al., 2002; Sun et al., 2006; Shao et al., 2006; Gasse et al., 1991; Tang et al., 1993; Liu et al., 2000; Qin et al., 2004). After the 4.2 ka BP cooling event, the Gansu-Qinghai region's cli- LIU Fenggui et al.: The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region 421

mate continued to be worsening. It was likely that 3.9–3.6 ka BP was the driest and coldest periods, when the forest area of the Qinghai Lake region was very small (Du, 1989) or had completely disappeared. Woodland prairie predominated the western Loess Plateau (Sun et al., 2009), which was similar to the present situation.

3 Evolution of Neolithic cultures in the Holocene Megathermal The climate change in Holocene had significant impacts on the Neolithic cultures in the Gansu-Qinghai region.

3.1 Expansion of Neolithic cultures in the early and middle periods of Holocene Megathermal

Consistent with Holocene climate change, as the climate warmed up again, the Neolithic cultures–Dadiwan Culture (7.8–7 ka BP), featured by the earliest hunting and slash and burn farming, emerged in some places with better natural conditions such as Weihe River basin, Jinghe River basin, upper and middle reaches of western Hanshui River across the border between Shaanxi and Gansu in the early period of Holocene Megathermal. In this period, Dadiwan Culture sites dominated a smaller scope and scale with low level of agricultural production. During the middle period, it was warm and humid in the Gansu-Qinghai region, and agriculture was developed with sufficient and stable food supply, thus the Neolithic cultures were flourished. Prehistoric human activities had been further expanded in a larger scale and geographic scope. Around 5.9 ka BP it had entered the river valleys on the Gansu-Qinghai border. In this period, Yangshao Culture (7–5 ka BP) formed, which was the most extensively distributed and lasted longest in the region east of the Tibetan Plateau. The number of its Neolithic sites found in Gansu Province exceeded 1400.

3.2 Northward and southward expansion of the Neolithic cultures during late Holo- cene Megathermal

After the 5.9 ka BP cooling event, the Neolithic cultures in the Gansu-Qinghai region extended into the Hehuang Valley in Qinghai. The Majiayao Culture (5.9–4.0 ka BP), featured by most developed agriculture and painted pottery, formed in the area west of the Liupan Mountains to the Huangshui Valley in Qinghai, as well as the northeast edge of Sichuan (Figure 2a). In this period, agriculture was mainly composed of millet and hempseeds, people had already begun raising pigs, dogs, sheep and other livestocks. In comparison to cultural types of the early and late Majiayao, the Neolithic cultures extended markedly to west and north. For example, the Majiayao Culture, which first extended into Qinghai, was considered as the transitional Shilingxia type (5.9–5.4 ka BP) from Yangshao Culture to Ma- jiayao Culture, mainly distributed in the Yellow River Valley in eastern Qinghai Province below 2500 m asl. The Shilingxia site was small (Figure 2a-1), lying to the east, and to the south. After nearly five centuries of development (around 5.4 ka BP), Majiayao cultural type (5.4–4.6 ka BP) and the Banshan cultural type (4.6–4.3 ka BP) had been widely distributed in the upper Yellow River and the Huangshui Valley at an elevation above 2500 m (Figures 2a-2 and 2a-3). In particular, the number of sites in the Machang type (4.3–4.0 ka BP) of the late Majiayao Culture exceeded 2400 in the Gansu-Qinghai region, with some sites distrib-

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uted above an altitude of 3000 m (Figure 3), and the northern boundary of the sites had also been extended north to Jiayuguan in the vicinity of 39.48°N (Figure 2a). This is because the relatively warm, moist and stable climate provided favorable conditions for the development of dry farming in the Gansu-Qinghai region, hence the northern boundary of Majiayao farming extended to the north by nearly 4 degrees in latitude, and increased by almost 1000 m in altitude.

Figure 2 Locations of Majiayao cultural sites in the Gansu-Qinghai region LIU Fenggui et al.: The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region 423

Figure 3 Statistics of Majiayao cultural types in the Qinghai region by elevation

3.3 Retreat of Neolithic cultures towards south-east in the late period of Holecene Megathermal

After the 4.2 ka BP cooling event, the climate continued to deteriorate. Qijia Culture (4.0–3.6 ka BP) of the Gansu-Qinghai region had two major features in the late period of the Holocene Megathermal (Figure 4). First, the nature of production changed dramatically. Al- though Qijia Culture was featured by the cultivation of millet and other crops, bones of cattle, sheep, dogs and pigs were found in some places (Table 2) such as the Shenna site in Hehuang Valley (2200 m asl, 93.5% of sheep bones was unearthed in the Shenna site) as well as Qinweijia and Dahezhuang in the western Loess Plateau (GQWT, 1974; 1975). In the late period of Qijia Culture, the raising of cattle, horses and other large domestic animals started (Zhang, 1987), indicating that there was a marked increase in animal husbandry. The second is the apparent change in geographical distribution. GIS was applied to analyze Ma- jiayao and Qijia cultural sites in the Gansu-Qinghai region. There is a greater difference between Majiayao and Qijia cultures north of and south of 36°N. The number of Majiayao cultural sites north of 36°N accounts for 49.33%, and that of Qijia cultural sites and that of

Figure 4 Locations of Qijia cultural sites in the Gansu-Qinghai region

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Table 2 Statistics of animal bones unearthed in Qinweijia and Dahezhuang of Qijia Culture Pig bones Sheep bones Cattle bones Number Percentage (%) Number Percentage (%) Number Percentage (%) Qinweijia 430 83.0 50 9.7 38 7.3 Dahezhuang 194 72.9 56 21.1 6 2.3

Qijia cultural sites takes up only 17.25%; while to the south of 36°N, Majiayao accounts for 50.67%, and Qijia is 82.75%. It is calculated that the center of gravity of Majiayao Culture is located at 35°58'N and 103°55'E, and that the center of gravity of Qijia Culture is at 35°34'N and 104°53'E. The center of gravity of the cultural system moved eastward about one degree of longitude, and southward by about half of one degree in latitude (Hou et al., 2009). It is estimated that the average height of Majiayao Culture is 2000 m asl. As for Qijia Culture, nearly 48.6% of the sites are located at an altitude of 1900 m asl. The proportion was much higher than that of the Majiayao Culture (Hou et al., 2009), decreasing from high mountains to the low-lying valley areas (Liu et al., 2005). In terms of geographical range, the Majiayao Culture can only be found to the west of Liupan Mountains to extending in a clear north-south direction, indicating that the northern boundary of dry farming was still at relatively high latitudes, while the Qijia Culture expanded in the east-west direction, and went across the Liupan Mountains to appear in the Jinghe River Valley. This characteristic was due to the fact that the northern boundary of dry farming was restricted by the temperatures, thus it could only extend in the latitudinal direction.

3.4 Formation and development of multiple cultures after the Holocene Megathermal

3.9–3.6 ka BP is the driest and coldest period in the Gansu-Qinghai region since the Holo- cene Megathermal (Shi, 1992), and it is also a period of frequent occurrence of extreme climate events (Xia, 2003). After the Neolithic cultures of the Gansu-Qinghai region experi- enced a nearly 300-year period of low temperatures and extreme climate, its unified and well-developed farming cultural system completely collapsed. There was a marked reduction in the number of Qijia cultural sites after 3.9 ka BP, and an evidence of a significant increase of animal husbandry occurred in the burials (Table 2). Through adaptation and revolution, the Neolithic farming culture shrinking to a few parts of the regions, developed specializa- tion; i.e., the first social division of labor in human history around 3.6 ka BP. Later No- madism was separated from farming cultural system, hence multiple cultures began to take shape. Afterwards, animal husbandry-based Kayue Culture began to flourish in the moun- tainous areas of Qinghai over 2500 m asl, with the upper limit being about 4000 m. In the relatively low and moderately warm Yellow River Valley on the border between Gansu and Qinghai, Xindian Culture (3.6–2.6 ka BP) inherited farming techniques from Qijia Culture and survived. In the relatively high part of southwest Gansu, Siwa Culture (3.4–2.5 ka BP) appeared with the animal husbandry or farming-pasturing as the main sector (Yu, 1985; Xu, 1988) (Figure 5), which was partly associated with Kayue Culture. On the southern tip of Hexi Corridor emerged Siba Culture (3.9–3.4 ka BP), featured by wheat and a large amount of painted pottery, which was affected not only by the Neolithic cultures of the Gansu-Qinghai region, but also by those of the Central Asia, as well as by Shajing Culture LIU Fenggui et al.: The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region 425

Figure 5 Changes of temperature, precipitation and prehistoric cultures in the Gansu-Qinghai region

(3–2.5 ka BP) taking animal husbandry as the main sector and having the latest painted pottery in China. Hence, after experiencing the 4.2 ka climate change event, the Neolithic farming culture had a sudden collapse and was split into several local cultures, instead of the previous integration. It is worth noting that social industrial division of labor at the 3.9–3.6 ka BP in the Gansu-Qinghai region is the most important reason for the formation of multiple cultures. Some studies consider that the beginning of human civilization was closely related to the social division of labor, that is, the division of agriculture and nomadic animal husbandry marked the end of primitive society and the beginning of civil society (Burns et al., 1998; Morgan L H, 1977; Morgan M, 1965). A large number of studies on the Gansu-Qinghai region indicate that the divide between rich and poor appeared in the late Qijia Culture (Xie, 2002), which might have entered the end of primitive society, while Kayue Culture rising around 3.6 ka BP might have entered the slave society (Gao, 1993), which coincided with the rise of Xia civilization on the Central Plains. From this, we can see that the 4.2 ka BP climatic cooling event may be an important sign of the end of primitive society in the Gansu-Qinghai region. From the viewpoint of the Neolithic farming culture in the Gansu-Qinghai region in re- sponse to climate change of the late period of Holocene Megathermal, Qijia Culture was greatly affected by latitude and altitude. It is deduced that the northern boundary of dry farming of Qijia Culture was one degree lower in latitude than that of Majiayao Culture (with the northernmost being 39°N in the vicinity of the Jiayu Pass), while that of Qijia Culture reduced to about 38°N near the Wuwei region. This indicates that the 4.2 ka BP climatic cooling event restricted dry farming in marginal areas of the Tibetan Plateau and farming-pastoral areas of northern China forcing the humans to either 1) relocate towards low latitudes and low altitudes where the temperature is suitable, or 2) to change their production patterns, using the same cultivation technology. As the temperature conditions were

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similar to modern conditions around 4.2 ka BP, we can interpret the past spatial distribution of drying farming and animal husbandry in the Gansu-Qinghai region according to distribution of modern accumulated temperatures. The analysis of the use of overlaid modern grid- ding data of ≥ 10℃ and cultural heritage sites (Figure 6) shows that the spatial pattern of multiple cultures after 3.6 ka BP is well consistent with the distribution of modern accumulated temperatures of ≥10℃ isotherms. Kayue cultural sites are mainly located in a range of 500–2000℃ (≥10℃ accumulated temperatures). Huang Bingwei’s studies suggested that the lower limit for grain production on the Tibetan Plateau is 50 continous days of ≥10℃ (the minimum accumulated temperatures of at least 500℃), and that its condition for stable production is ≥140 continous days of ≥10℃ (accumulated temperatures of over 2000℃) (Huang, 1959). It can be deduced that 500–2000℃ accumulated temperatures may be a very unstable condition for grain production. Therefore, Kayue Culture should not be dependent on the cultivation of crops as the main source of food. The statistics of the car- bonized crops unearthed at Kayue cultural sites of Fengtai, Huzhu County, Qinghai (2500 m asl, about 1500℃ of ≥10℃ accumulated temperatures) show that, barley (naked barley) accounted for 92%, millet, 5%, wheat, 3% (Fang and Sun, 1998). Meanwhile, an abundance of ram horn bones, horse bones, cattle foot bones, and sheep manure were found at the Ka- yue cultural sites in Tawan, Huangyuan County, Qinghai, and Xunhua Thoron Ahart Lacayo, and other evidence (ATQ and QHCM, 1985). All these evidences (ATQ and QHCM, 1985) show that the crops at that time were mainly barley (naked barley) and others that were suitable for high-altitude and low temperature conditions, and that livestock had a large part to play in human life. Xindian cultural sites are mainly distributed in the low-altitude and river-valley regions above 2000℃ with ≥10℃ accumulated temperatures. 2000℃ (≥10 ℃ accumulated temperatures) is just the divide between cool-loving and thermophilic crops, and it is a condition for the stable grain production on the Tibetan Plateau, which is the root cause that Xindian Culture took agricultural production as the main sector.

Figure 6 Locations of Kayue, Xindian and Siwa sites of the Neolithic cultures and modern accumulated temperatures of ≥10℃ in the Gansu-Qinghai region LIU Fenggui et al.: The impacts of climate change on the Neolithic cultures of Gansu-Qinghai region 427

4 Conclusions (1) The climate change in the early, middle and late periods of the Holocene Megathermal was consistent with the development of Neolithic cultures in the Gansu-Qinghai region, which well explains the evolution of man-land relationship in the Neolithic age. (2) The Gansu-Qinghai region, a transitional area between the Tibetan Plateau and the Loess Plateau, is relatively sensitive to climate change. In the early and middle periods, the climate became warm and humid, which promoted great development of Neolithic cultures based on dry farming. Hoe farming culture starting at 7.8 ka BP was developed into Yang- shao Culture in the heyday of the Holocene Megathermal. (3) The 5.9 ka BP cooling event marked the beginning of a colder period in the Holocene Megathermal, but the climate was relatively warm, humid and stable at 5.9–4.2 ka BP compared to the present, which created conditions for the development of Majiayao farming culture. Thus the Neolithic cultural sites extended northward and westward, being four latitudes to the north and nearly 1000 m up in altitude. (4) The climate continued to deteriorate from the 4.2 ka BP cooling event onwards, which exerted a great impact on the Neolithic cultures in the Gansu-Qinghai region. The then temperature which restricted the dry farming forced Qijia Culture around 4.2 ka BP to shrink towards low-altitude and low-latitude regions. It was inferred that the northern boundary of agricultural production of Qijia Culture period was a latitude degree lower than that of Ma- jiayao Culture period, and the altitude was down to below 1900 m above sea level. (5) The period 3.9–3.6 ka BP saw the driest and coldest climate as well as frequent extreme events in the Gansu-Qinghai region, resulting in the first division of labor of human society, that is, animal husbandry was officially spun off from agriculture, and the unified Neolithic farming culture completely collapsed. Animal husbandry predominated the region with 500–2000℃ (≥10℃ accumulated temperatures), accompanied by cool-loving crops hence Neolithic animal husbandry culture formed. Meanwhile, Neolithic farming culture remained in the region of over 2000℃ (≥10℃ accumulated temperatures), with the thermophilic crops as the main grain. It is considered that such industrial division of labor ultimately led to the end of primitive society, and civil society began to take shape.

Acknowledgments The authors would like to express their sincere thanks to Prof. Fang Xiuqi from Beijing Normal University for his constructive suggestions that greatly improved this manuscript, as well as Dr. Ran Min from Lanzhou University for providing some information, and Yang Yuhan, a master from Qinghai Normal University, for collecting the materials, in the prepa- ration of this paper.

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