A three-group age structure can be designated as a point in the triangular diagram, while the routine of the points in time series traces the age structure evolution. The paper classifies the age structure evolution patterns of countries (areas) in the world and provinces in China, and discovers the general and ergodic age structure transition (AST) pattern which experiences three stages: the “bonus raising” stage (i.e., from the traditional fertile young population to fewer children-more labors population), the “debted ageing” stage (i.e., from fewer children-more labors population to fewer labors-more aged population), and the stage in between (i.e., turning stage). While developed countries are primarily in the middle of stage three, most developing countries are in the late phase of the first stage, and many least developed countries in Africa are still in the early stage one or even in the traditional position. Started in the 1950s and accelerated since the 1980s, the AST in China is now just passing the turning stage with diversifying decreasing bonuses at turning points from coast to inland provinces. According to a simulation scenario, China will approach the equilibrium position near 2100, with 15% children, 55% labor forces, and 30% older people, which is probably the common end of all countries in the future.

This paper constructs an explanatory model of fertility changes based on social dynamics, which consists of three factors affecting human reproductive behavior, including fertility intentions, contraceptive barriers and competing preferences. The changes in the relative effects among these three factors contribute to three stages of fertility change in human history: natural fertility, shrinking fertility and suppressed fertility. In China, family planning policy is the fourth factor. With the promotion, implementation and relaxation of the family planning policy, Chinese reproductive behaviors have adjusted accordingly, leading to fluctuating fertility rates. The building-up of market economy in early 1990s stimulated the competing preferences. Based on data for East China from the 2017 fertility survey, this paper examines trends in total fertility rate, marital duration-specific fertility rate and parity-specific total fertility rate. With Shanghai in center, fertilities by provinces differ latitudinally. We also show the changes of monthly distribution of births since 2012 to see the influence of family planning policy adjustment.

China has been urbanizing and big cities have been growing rapidly.Number of megacities in China increased from 34 in 1997 to 63 in 2007.There are substantial disputes over China’s urbanization strategy to prioritize big cities or medium and small-sized cities.Development of big cities faces challenges in transportation,housing,environment and resources and public services,and population control becomes increasingly important in big cities.This issue of Population and Development Forum is specifically devoted to population control in China’s megacities,for which three population experts were invited to share their views and suggestions.Professor Huang Ronglong,from Nanjing Normal University,argues that the major cause of China’s urban disease is not overpopulation but ill management of the cities.However,Professor Ding Jinhong,from East China Normal University,has a different view and asserts that a permanent cure to urban disease is population control.Talking on population control in Beijing,Professor Duan Chengrong,from People’s University of China,suggests the population control strategy be changed from a local to a national perspective.Three experts also provide policy suggestions in population control,city planning and management,industrial upgrading,mechanisms in evaluating demographic effect of social and economic programs,etc.Professor Liu Feng,from Development Research Center of the State Council,chairs the Forum and provides comments to the three papers and his own opinions as well.