Two universal pathways in demographic transition.

Area of Science:

• Demography
• Sociology
• Economics

Background:

• Demographic transition, marked by falling fertility and mortality, is a global phenomenon linked to modernization.
• Existing models of fertility decline are primarily based on Western countries, leaving applicability and mechanisms in other regions unclear.

Purpose of the Study:

• To identify universal pathways and underlying mechanisms of demographic transition across diverse global regions.
• To analyze changes in crude birth rate (λ) and life expectancy (e₀) from 1800-2020.

Main Methods:

• Utilized global data from 237 countries and territories spanning 1800-2020.
• Identified two distinct pathways governing demographic trajectories (Phase I and Phase II).
• Developed a theoretical model based on the trade-off between reproduction and education to explain phase transitions.

Main Results:

• Two universal pathways (Phase I: conserving λe₀; Phase II: conserving λexp(e₀/17)) were identified, governing most countries' demographic trajectories.
• Phase I (pre-1950) was characterized by high child mortality and steady population growth.
• Phase II (post-1950) is marked by low child mortality, steady GDP per capita growth, and is accelerated by factors like declining educational costs and Westernization.

Conclusions:

• Demonstrates quantitative regularities in fertility and longevity during demographic transition.
• Provides a theoretical framework for understanding the mechanisms driving demographic shifts globally.
• Highlights the role of modernization, education, and social factors in accelerating the transition to Phase II.