Stage 4: Post-Industrial
Birth rates equal mortality rates, and zero population growth is achieved. Birth
and death rates are both relatively low, and the standard of living is much higher
than during the earlier periods. In some countries, birth rates may actually fall
below mortality rates and result in net losses in population. Examples of
declining populations include Russia, Japan, and many European countries. The
developed world currently remains in this fourth stage of demographic
transition.
Stage 5: Sub-Replacement Fertility
The original demographic transition model has just four stages; however, some
theorists consider that a fifth stage is needed to represent countries that have sub-
replacement fertility (that is, below 2.1 children per woman). Most European and
many East Asian countries now have higher death rates than birth rates. In this
stage, population aging and population decline will eventually occur to some
extent, presuming that sustained mass immigration does not occur.
Figure 6.10 Demographic transitions occurring in human populations
AGE-STRUCTURE DIAGRAMSA good indicator of future trends in population growth is furnished by age-
structure diagrams. Age-structure diagrams are determined by birth rate,
generation time, death rate, and sex ratios. There are three major age groups in a
population: pre-reproductive, reproductive, and post-reproductive. A pyramid-
shaped age-structure diagram (e.g., Nigeria) indicates that the population has
high birth rates and the majority of the population is in the reproductive age
group (generally late teens to mid-40s). A bell-shape indicates that pre-