The reproductive cycle refers to the process from a woman's first to last birth. Through a systematic categorization and analysis of the evolution of reproductive cycles across global regions, combined with theoretical discussions on long-term demographic development, this study reveals that reproductive cycle evolution exhibits significant ergodicity, termed the Reproductive Cycle Transition (RCT). The RCT progresses through four stages: a Steady-State Stage, a Compression Stage, a Leveling-Off Stage, and an Equilibrium Stage. It shifts from a traditional pattern characterized by a low age at first birth, a high age at last birth, and a long reproductive span (“low-high-high”) to a modern pattern characterized by a high age at first birth, a low age at last birth, and a short reproductive span (“high-low-low”). The RCT parallels the fertility transition. Europe, North America, Australia, New Zealand and East Asia have entered the Leveling-Off Stage. In contrast, most of Asia, Africa, and Latin America are in the late stage of the Compression Stage, while East, Central, and West Africa remain in their early stage. China's reproductive cycle exhibits an accelerated pattern, beginning in the 1960s and entering the Leveling-Off Stage by the early 1990s. The shortening of the reproductive span carries the risk of lowest-low fertility. Fertility support policies should target the distinct fertility needs of women across different age groups.

Based on the panel data of China's prefecture-level cities in 2000, 2010, and 2020, this paper examines the spatial effects of population ageing on technological innovation and explores the heterogeneous impacts of ageing on technological innovation at different stages of social and economic development. The analytical results of the spatial Durbin model exhibit a robust inverted U-shaped relationship between population ageing and local technological innovation, as well as a U-shaped relationship between population ageing and neighbors' innovation. Furthermore, the threshold regression models indicate that, at the stage of low urbanization rate and insufficient supply of health services, population ageing imposes a significantly negative impact on technological innovation. With higher urbanization and a more adequate supply of health services, population ageing would stimulate innovation. Therefore, against the backdrop of the irreversible ageing process, promoting the urbanization process and improving the health care system will effectively attenuate the discouraging effects of ageing on innovation.

Based on the dynamic panel data for 31 provinces in China between 2000 and 2018, this paper examines the heterogeneous impacts of population ageing on technological innovation. We apply the system GMM method and reveal a humpshaped relationship between population ageing and innovation. Moreover, as compared with incremental innovation, population ageing poses a more noticeable negative impact on radical innovation at an earlier stage. We further employ the dynamic threshold regression to explore the nonlinear relationship between ageing and technological innovation. The results confirm the threshold effect of urbanization. In other words, once urbanization is below 86%, population ageing inhibits innovation.Otherwise, it could promote innovation. Therefore, the urbanization process could efficiently attenuate the discouraging effect of ageing on innovation.

Drawing upon provincial data between 1995 and 2015 in China, this study presents the regional distributions and dynamic changes of residential energy consumption per capita, and also investigates the impacts of population structure and household size on residential energy consumption. Residential energy consumption per capita is on a rising trend across China, and the annual growth rates in Heilongjiang, Hainan, and Chongqing provinces between 2005 and 2015 top the list. Empirical analyses reveal that there is a U-shaped correlation between urbanization and residential energy consumption, and moreover, population aging and the shrinkage of household size lead to the increased energy consumption. In order to achieve the dual targets of combating climate change and meeting the rising demand for prosperous life, China should further promote energy reservation, and more importantly, improve the energy consumption structure and expand the utilization of clean energy.

Employing the 2002 household survey data in 9 provinces in East China，this paper examines
the effect of family structure on female and male labor force participation．Constructing regression models with instrument variables to correct for the endogeneity of family structure，our results indicate that intergenerational coresidence significantly increases female labor force participation and weekly working time，while it has no effect on male labor supply．A major reason is that coresidence help to reduce female housekeeping burden through their parents' assistance，which frees up time for work in labor market．These results suggest that decline in intergenerational coresidence in the past two decades could contribute to the more rapid decrease in female labor force participation in China．