Demographic transition is a theory that proposes three distinct stages in the gradual shift of population groups from high fertility and mortality to low fertility and mortality. These include the pretransition, transition, and post-transition phases, which have different relationship dynamics between mortality and fertility (McCracken & Phillips, 2017). The pretransition step implies high death and birth rates to support the population, as those effectively cancel each other out. The transition stage begins when the population starts growing rapidly due to the decline in the death rate that is not balanced by the corresponding decrease in the birth rate yet. People still tend to have many children, and most of them survive, in sharp contrast to the previous demographic stage. Finally, the post-transition phase marks the development of a new lower-quantity balance between mortality and fertility, as new generations of people adapt to the changing conditions and choose to have fewer kids.
During the pretransition period, the population is relatively young, and in the post-transition stage, the average age is much higher. The reason for that is that life expectancy grows rapidly during the demographic transition, and the share of older people in the population increases (Sarukhan, 2017). In this framework, it is essential to take into account the epidemiological transition as well. Epidemiological transition focuses on causes of mortality, emphasizing the shift from infectious diseases and reproductive conditions to chronic non-communicable diseases as the main risk factors (Hazra & Gulliford, 2017). The epidemiological transition also has three major stages closely associated with the respective demographic stages (McCracken & Phillips, 2017). The first stage is associated with constant famines, epidemics, and wars, which keep the mortality high. The death rates drop quickly in the second stage when epidemics become less common, and in the third stage, degenerative-disease dominance over infectious diseases is fully established. This shift away from communicable diseases is one of the main factors that positively affected the average life expectancy of population groups and allowed a larger proportion of people to live to old age.
When considering the aging population, demographic and epidemiological perspectives are still the main explanatory theories that demonstrate the logic behind the global shift to the aging world. Therefore, despite the ongoing debates about some sub-factors, such as the role of nutrition and healthcare, the usefulness of demographic and epidemiological prisms is beyond scientific doubt. Throughout history, in different countries and regions of the world, variations within the demographic transitions have occurred; however, generally, all the population groups follow the same trends and stages. For instance, Bangladesh and Sri Lanka are examples of countries that achieved a drop in death and birth rates without corresponding significant social and economic changes (McCracken & Phillips, 2017). Nevertheless, such cases mostly helped improve the theory and make it more complex. Therefore, it can be said that demography and the previously mentioned trends and changes are inevitable.
Gerontology studies aging and its various aspects, including the biological, psychological, social, cultural, and cognitive ones. All of the mentioned claims considering demographic and epidemiological transitions, lead to the conclusion that every population group will inevitably pass through all of the stages of the changes. This means that the relevance of gerontology will steadily grow with time, as more societies will join the most developed countries in the third demographic stage.
References
Hazra, N.C., & Gulliford, M. (2017). Evolution of the “fourth stage” of epidemiologic transition in people aged 80 years and over: Population-based cohort study using electronic health records. Population Health Metrics, 15(18). Web.
McCracken, K., & Phillips, D. R. (2017). Demographic and epidemiological transition. International Encyclopedia of Geography: People, the Earth, Environment and Technology, 1–8. Web.
Sarukhan, A. (2017). The epidemiological transition (or what we died, die and will die from). The Barcelona Institute for Global Health. Web.