Peru is best known as the heart of the Inca empire, but it was home to many diverse indigenous cultures long before the Incas arrived. Although there is evidence of human habitation in Peru as long ago as the eighth millennium BC , there is little evidence of organized village life until about 2500 BC. It was at about this time that climatic changes in the coastal regions prompted Peru’s early inhabitants to move toward the more fertile interior river valleys. Today, Peru’s population of about 23 million is divided almost equally between the highlands and the population centers of the coast, and the division marks a sharp cultural as well as geographic divide.