The Middle Holocene epoch (8,000 to 3,000 years ago) was a time of dramatic changes in the physical world and in human cultures. Across this span, climatic conditions changed rapidly, with cooling in the high to mid-latitudes and drying in the tropics. In many parts of the world, human groups became more complex, with early horticultural systems replaced by intensive agriculture and small-scale societies being replaced by larger, more hierarchial organizations. explores the cause and effect relationship between climatic change and cultural transformations across the mid-Holocene (c. 4000 B.C.).