Archaeologists have studied human skeletons unearthed in the Andes from 900 to 2800 years ago. Some chemical isotopic compositions extracted from them reflect that people there ate corn at that time. The corn culture led to the population growth in the Andes. Several large-scale wars at that time were also related to the competition for scarce soil suitable for planting corn, The war led to the continuous change and development of the social system. 
Inca civilization in the Andes experienced several major social changes as early as 2800 years ago
 they concluded that agriculture promoted the development of ancient Andean society.