The Early and Middle Jōmon periods see an explosion in population, as indicated by the number of settlements from this period.

These two periods occur during the prehistoric Holocene Climatic Optimum (between 4000 BCE and 2000 BCE), when temperatures reach several degrees Celsius higher than the present, and mean sea level is higher by five to six meters.

Beautiful artistic realizations, such as highly decorated "flamed" vessels, remain from this time.