About 5,500 years ago, a global climate change occurred and the average temperature dropped by two to three degrees centigrade due to solar activity and the orbit of the earth, geologist Liu Dongsheng told Xinhua.

Liu, an academician of the Chinese Academy of Sciences, said the glaciers in the western part of China advanced forward during that period and the development of ancient soil of the Loess Plateau in northwest China stopped, while the cold resistant spruce prospered in regions such as today's Beijing.

More and more archaeological discoveries seem to indicate there was also a social change in China during that time. The poor and the rich were differentiated in human society, and people were divided into different social strata.

Archaeologists have found ancient settlement centers and tombs of aristocrats in the relics of that period. Weapons became popular funeral objects, which mean that wars were common at that time. And then castles appeared. All of these are deemed as signs of emerging civilization, said archaeologists.

Wu Wenxiang, a scholar with the Urban Environment Department of Peking University, explained that the sudden change of climate caused a sharp decrease of food and intensified the conflict between population and resources.

As a result, the ancient Chinese migrated from outer areas to the center regions, from high land to low altitude places which were more comfortable to live in, said Wu.

During the process of scrambling for resources, the concept of private property appeared, and people's praying for favorable weather led to the development of religion, Wu said.

But the overall environment was still suitable for human development. The climate played an important role in human social development, but it was not a determinative factor, said Wu.

Scientists have found that the climate change did not always push forward the development of civilization, but sometimes caused disasters.

The climate became remarkably cold again about 4,000 years ago, which many foreign scholars believe is the main reason of the collapse of the ancient civilizations in Egypt, Indus and the Mesopotamian.

China has many legends about floods during that period. Chinese archaeologist Yu Weichao attributed the decline of the Liangzhu and Longshan cultures on the lower reaches of the Yangtze and Yellow rivers to serious floods about 4,000 years ago.

"The floods turned the lower reaches of the Yangtze and Yellow rivers, especially the Yangtze delta, into boundless water. Most of the facilities of the formerly prosperous Longshan and Liangzhu cultures were suddenly destroyed when their farmland was inundated," said Yu.

He added that production stopped, along with the development of civilization.

Wu Wenxiang said that when the Longshan and Liangzhu cultures were declining, the Xia Culture was rising in central China during the climate change, initiating China's first dynasty, Xia (about 2070-1600 BC). More studies are needed to explain why, Wu added.

The relationship between climate change and the evolution of civilization has drawn the attention of many scientists, who presume that the fluctuation of climate is favorable for the survival of the fittest.

Chinese archaeologists and scientists have begun a project to find the origin of ancient Chinese civilization. They listed environmental change and civilization development as an important research subject.

(Xinhua News Agency February 11, 2003)