## 4 Discussion
### Climate Variations in Linkage to Prehistoric Occupation  
Research on the Paleolithic climate in the middle reaches of the Yuanjiang River was somewhat limited, primarily relying on insights derived from glacial deposits. However, the lower reaches, particularly the Dongting Lake Plain, have yielded more extensive climate studies [30; 36; 48; 49; 50; 51; 52; 53; 54]. Analysis of Paleolithic sites in both the middle and lower reaches of the Yuanjiang River revealed that their distribution across the first, second, and third level terraces, with 39, 63, and 15 sites, respectively. Despite potential discrepanciesbetween the archaeological data and regional climate records, a clear relationship between site numbers and climate conditions emerged (Figure 5). During the early Middle Pleistocene, a cold and dry climate created unfavorable conditions for human development. However, as temperatures warmed during the middle Pleistocene, human activity in the region increased and continued into the late Pleistocene. This warming trend supported greater human occupation, as evidenced by the rising number of archaeological sites (Figures 3 and 5). A subsequent cooling phase in the late Pleistocene, however, hindered further expansion, leading to a decline in site numbers. During the Lower Zaoshi culture period (7800-6300 BP), which coincided with the river or lake-cutting phase and the expansion of Dongting Lake, the number of archaeological sites remained relatively low. This suggests a weak correlation between environmental changes and human activity. In contrast, the Daxi culture period (6300-5300 BP) aligned with a \"warm and slightly dry\" Holocene optimum climate and the peak expansion of Dongting Lake (Figure 5). To avoid flooding, human populations likely sought higher ground, although some sites within the lake area indicate an adaptation to living near or on the water, showcasing an important development in environmental manipulation. In the Quijailing culture period (5300-4600 BP), the warm Holocene climate persisted, but  
Figure 5: Paleoclimate changes in the Dongting lake and neighboring areas since the mid-Pleistocene [7; 36; 48; 50; 54]. trends toward hotter and wetter conditions emerged. The number and distribution of archaeological sites remained similar to those of the Daxi period. The transition from the Qujialing to the Shijiahe culture marked a period of rapid cultural development differing from earlier patterns. This shift suggests that sudden external factors, such as the climate change event around 4.2 ka BP, played a crucial role in human development, as highlighted in previous studies [55; 56; 57]. This event, part of the larger mid-to-late Holocene climate shift, proved to be a significant turning point for human civilizations. In some regions, ancient cultures declined, while in others, such as the middle reaches of the Yuanjiang River, agricultural development accelerated after a period of adaptation, leading to rapid human expansion. These findings align with the results of the current study. During the subsequent Shijiahe culture period (4600-3600 BP), ancient cultures flourished, particularly in the lower reaches of the Yuanjiang River, where human settlements expanded significantly. Environmental constraints that had previously influenced settlement patterns diminished, allowing communities to inhabit areas beyond high river floodplains or terraces. Evidence of small dwellings suggested the emergence of private spaces, marking a shift away from communal living. In the Shang and Zhou dynasties (1600-256 BC), cultural sites, particularly those associated with the Wushui cultural group, became more widespread, forming large communities along the river basins. While the distribution of sites in the lower reaches overlapped with those of the Neolithic period, the number of lakeside settlements decreased significantly.