Demography transition 1-1
Study of human populations, features ( sex ratio, dependency ratio and age structure) growth and decline due to changing patterns of migration fertility and mortality.
Formal theory by FW Notestein. 1945. Population undergoes three stage sequence associated with economic development.
I stage. High fertility and mortality. Backward country with agrarian economy poor diet sanitation medical facilities illiteracy early marriage etc. Amazon tribes.
II stage. Rising income levels industrial economy, better diet, transportation, food supply, medical advances. Death rate declines but birth rate remains high as society slow to change. Ethiopia
III stage. Rising education, women empowerment, social change, education, rational thinking. Decline birth rate. Population stabilizes. USA
But today aging population and declining overall is observed in countries like Japan.
Murray et al note set that of communicable diseases has declined but non communicable diseases of modernity like hypertension drug use alcoholism obesity diabetes are Rising.