The second stage of the model, often called the “early expanding” or “early
industrial” stage, reflects the impact of advancements in food production and
medical science on the death rate. Technological achievements in science and
the mechanization of agriculture have the result of dramatically reducing the death
rate and expanding life expectancy. This results in more people living longer, as
well as lower infant mortality, meaning that more individuals survive to adulthood.
The birth rate, however, remains unchanged, or perhaps may even decline slightly
during this stage. The plunging death rate, however, causes a disparity with the rel-
atively constant birth rate, resulting in rapid population increases. The death rate
declines throughout this entire stage, although toward the end of the period it
begins to level off, as the impact of technological advancement on life expectancy
and mortality diminishes. A population pyramid of this stage indicates much less
tapering toward the apex of the pyramid (a much larger number of people living
into old age), but retaining its broad base, because birth rates have not significantly
changed from the first stage. Many countries of the “developing world” are consid-
ered by proponents of the model to be currently experiencing this stage.
In stage three, or the “late expanding” portion of the model, the death rate has
stabilized at a low level, and the birth rate now declines rapidly. Population growth
continues at almost the same rate as in the early expanding period however,
because although the birth rate is falling, the death rate has dropped to such a
low point that births stillexceed deaths by a sizable margin, resulting in overall
population growth. The decline in the birth rate during this stage is generally
caused not by scientific or technological progress as was the case in the second
stage, but by shifts in social values and traditions, often having to do with the role
of women in society. For example, during stage three, women may enter the work
force in proportionally large numbers compared to stage two, or larger numbers of
women may pursue higher education, the widespread use of contraception and
abortion may become more socially acceptable, both women and men may delay
marriage until later in life, and average family size will typically decline along
with the total fertility rate. All of these changes in fact occurred in the United
States during the 1960s and 1970s, and supporters of the model generally place
the United States in the later phases of stage three. A pyramid representing this
stage would not preserve much of a traditional shape; rather, the base of the struc-
ture would be only slightly broader than the apex, especially a pyramid illustrating
the latter part of stage three.
The fourth and final stage of the model, the “postindustrial” stage, is character-
ized by both low birth and death rates in the population. Life expectancies remain
high, but the population in question has achieved a zero growth rate and possibly
even is reproducing at a rate below replacement value. The total fertility rate, in
other words, has declined to about two or even lower, meaning that couples are94 Demographic Transition Model