## 3 Results
### Spatial-Temporal Evolution  
From the Paleolithic era to the Shang and Zhou dynasties, the overall number of ancient cultural sites along the Yuanjiang River increased, yet growth trends differed between the middle and lower reaches. In the lower reaches, the total number of sites continued to rise, although the growth rate during the Shang and Zhou dynasties was notably lower than that during the Neolithic period, which saw the establishment of a broad distribution of cultural sites (Figure 3). In contrast, the middle reaches experienced a decline in the number of ancient cultural sites during the Neolithic, diverging from the trend in the lower reaches (Figure 3). However, there was a substantial increase during the Shang and Zhou dynasties, surpassing the growth in the lower reaches. This comparison suggested that the development of ancient cultural sites in these regions evolved independently over time, exhibiting distinct evolutionary characteristics.  
Spatially, archaeological sites in the middle and lower reaches of the Yuanjiang River can be divided into two primary areas: the downstream plain, with elevations below 100 m, and the middle intermountain basin, which typically ranges from 100 to 500 m (Figure 3). The central areas of these two regions have undergone shifts over time. From the Paleolithic to the Neolithic period, the center of ancient cultural development in the middle reaches shifted northward. Notably, the number of sites in the downstream areas of the Wushui River and Wushui River systems--where Paleolithic cultures thrived--declined during the Neolithic. Conversely, the Chen River system, extending northward from the Wushui River, experienced a significant increase in sites, forming a new cultural center within a circular area comprising the Chen River, Wushui River, and the mainstream of the Yuanjiang River. From the Neolithic to the Shang and Zhou dynasties, ancient culture in the middle reaches of the Yuanjiang River flourished, with a substantial expansion in the overall distribution. Numerous ancient sites have been identified across various tributaries, resulting in a relatively uniform distribution. Nevertheless, the northward shift in the center of cultural development remains evident (Figure 3). Clusters of sites emerged where the You, Wu, and Chen rivers intersected with the mainstream of the Yuanjiang River, particularly in Chenxi, Luxi, and Yuanling counties, while the significance of the Wushui River system diminished. During the Shang and Zhou dynasties, additional concentrated archaeological sites appeared in Yongshun and Baojing counties, located in the northwest of the middle and lower reaches. This region, characterized by a higher altitude and distance from the main river, formed a relatively independent cultural zone (see Figure 3).  
In the lower reaches, ancient cultural sites from the Paleolithic to the Shang and Zhou dynasties were primarily concentrated in the modern urban area of Changde City (Figure 3). Sites from different periods tended to shift either westward or eastward around this urban center. The number of ancient cultural sites in the lower reaches significantly increased from the Paleolithic to Neolithic periods, rising from 17 to 88 sites. This expansion resulted in a rapid increase in cultural distribution, with the center of development still located in Changde City but showing a clear eastward migration toward the Dongting Lake area. Numerous archaeological sites have been discovered around the lake, with some even being submerged. From the Neolithic to the Shang and Zhou dynasties, the number of archaeological sites continued to grow, with a uniform expansion in all directions (Figure 3f). However, during this time, the center of ancient cultural development shifted southwest of Changde City, leading to a decrease in sites to the east. In the Dongting Lake area, only a few archaeological sites were found, and none were located within the lake itself.