THE DEMOGRAPHIC TRANSITION Keith Montgomery Department Of Geography And

the demographic transition keith montgomery department of geography and geology the demographic transition is a model that describes po

THE DEMOGRAPHIC TRANSITION
Keith Montgomery
Department of Geography and Geology
The "Demographic Transition" is a model that describes population
change over time. It is based on an interpretation begun in 1929 by
the American demographer Warren Thompson, of the observed changes, or
transitions, in birth and death rates in industrialized societies over
the past two hundred years or so.
By "model" we mean that it is an idealized, composite picture of
population change in these countries. The model is a generalization
that applies to these countries as a group and may not accurately
describe all individual cases. Whether or not it applies to less
developed societies today remains to be seen.
Before proceeding you should review some demographic terminology or be
sure to follow the links given below as the terms arise.
The model is illustrated below:

As shown, there are four stages of transition. They will be described
first in terms of a typical fully developed country today, such as The
United States or Canada, the countries of Europe, or similar societies
elsewhere (e.g. Japan, Australia etc.).
STAGE ONE is associated with pre Modern times, and is characterized by
a balance between birth rates and death rates. This situation was true
of all human populations up until the late 18th.C. when the balance
was broken in western Europe.
Note that, in this stage, birth and death rates are both very high
(30-50 per thousand). Their approximate balance results in only very
slow population growth. Over much of pre-history, at least since the
"Agricultural Revolution" 10,000 years ago, population growth was
extremely slow. Growth rates would have been less than 0.05%,
resulting in long doubling times of the order of 1-5,000 yrs.

HIGHLIGHTS IN WORLD POPULATION GROWTH
1 billion in 1804
3 billion in 1960 (33 years later)
5 billion in 1987 (13 years later)
2 billion in 1927 (123 years later)
4 billion in 1974 (14 years later)
6 billion in 1999 (12 years later)
Given its characteristics, Stage One is sometimes referred to as the
"High Stationary Stage" of population growth ("high" birth and death
rates; "stationary" rates and "stationary" total population numbers).
Death rates were very high at all times in this stage for a number of
reasons, including:
*
Lack of knowledge of disease prevention and cure;
*
occasional food shortages.
Spikes in the rate of death were caused by outbreaks of infectious
diseases such as influenza, scarlet fever, or plague. However, on a
daily basis, it was primarily the lack of clean drinking water and
efficient sewage disposal, and poor food hygiene that created an
environment in which only a minority of children survived childhood.
Water and food borne diseases such as cholera, typhoid, typhus,
dysentery, and diarrhea were common killers, as were TB, measles,
diphtheria, and whooping cough. Today in the developed world, at
least, these are now minority causes of death.

Survivorship curve: Survivorship curves keep track of the fate of any
given birth cohort. They show the percent still living at a given age.
Nowadays in the developed world few children die before reproduction.
In Great Britain in 1999 only 1% of all children born alive died by
the age of five (compared to 10% in India, and 35% in Niger). However,
300 years ago it was quite a different matter, as the graph above
illustrates. In the City of York (England) in the 17th. Century, only
15% made it to the threshold of reproduction (15 yrs.). Only 10%
remained alive by the age of twenty. With so few females living to
reproduction, only a high fertility rate could maintain the
population. Note that changes with economic development, as shown by
Niger and India. Note also the impact of bias against females in India
on their survival -- otherwise, India's curve in 1999 is very similar
to Great Britain's for the late 19th. C. (not shown).
The high rate of birth (even higher if one were to adjust it for women
of childbearing age) could be due any or all of the factors that are
associated with high fertility even today in many less developed
countries. With a high death rate among children, there would be
little incentive in rural societies to control fertility except in the
most unbearable of circumstances.
Stage One, then, characterizes all world regions up until the 17th.C.
Some demographers sum up its character as a "Malthusian stalemate".
STAGE TWO sees a rise in population caused by a decline in the death
rate while the birth rate remains high, or perhaps even rises
slightly. The decline in the death rate in Europe began in the late
18th.C. in northwestern Europe and spread over the next 100 years to
the south end east. Data from Sweden clearly show this stage (and two
other stages following it):

The decline in the death rate is due initially to two factors:
*
First, improvements in food supply brought about by higher yields
as agricultural practices were improved in the Agricultural
Revolution of the 18th.C. These improvements included crop
rotation, selective breeding, and seed drill technology. In
England, the greater wealth this brought about enabled people to
marry earlier, thus raising the birth rate slightly at the same
time. Another food related factor was the introduction of the
potato and maize (corn) from the Americas. These new crops
increased the quantity of foodstuffs in the European diet,
especially in northern Europe.
*
Second, there were significant improvements in public health that
reduced mortality, particularly in childhood. These are not so
much medical breakthroughs (which did not come until the mid
20th.C.) as they are improvements in water supply, sewage, food
handling, and general personal hygiene following on from growing
scientific knowledge of the causes of disease. This is illustrated
below for the case of measles and TB in the USA over the past 100
years. However, bear in mind that killer infectious diseases such
as TB are airborne and not water borne, so public engineering
works such as sewer and water supply cannot take all the credit.
In fact, perhaps the most important factor here was increased
female literacy allied with public health education programs in
the late 19th. and early 20th. Centuries.


From the relationship between scurvy and measles in England and Wales
(scurvy is caused by a dietary deficiency in vitamin C), one could
surmise that general improvements in human well-being, an increase in
public health awareness, and a decline in poverty was most at work in
the decline of infectious diseases.

A consequence of the decline in mortality in Stage Two is an
increasingly rapid rise in population growth (a "population
explosion") as the gap between deaths and births grows wider. Note
that this growth is not due to an increase in fertility (or birth
rates) but to a decline in deaths. This change in population growth in
north western Europe begins the population rise that has characterized
the last two centuries, climaxing in the second half of the 20th.C. as
less developed countries entered Stage Two (next two plots):


(Source: WRI)
Another characteristic of Stage Two of the demographic transition is a
change in the age structure of the population. In Stage One the
majority of death is concentrated in the first 5-10 years of life.
Therefore, more than anything else, the decline in death rates in
Stage Two entails the increasing survival of children. Hence, the age
structure of the population becomes increasingly youthful. This trend
is intensified as this increasing number of children enter into
reproduction while maintaining the high fertility rate of their
parents. The age structure of such a population is illustrated below
by using an example from the Third World today:

Demographic Indicators
Birth Rate: 36 per thousand
Total fertility rate: 4.8 births
Natural increase: 2.9% per year 1990-2000
Age structure: 43% under 15 yrs.age
STAGE THREE moves the population towards stability through a decline
in the birth rate. This shift belies Malthus's belief that changes in
the death rates were the primary cause of population change.
In general the decline in birth rates in developed countries began
towards the end of the 19th.C. in northern Europe and followed the
decline in death rates by several decades (see example of Sweden, in
Stage Two above).

There are several factors contributing to this eventual decline,
although some of them remain speculative:
*
In rural areas continued decline in childhood death means that at
some point parents realize they need not require so many children
to be born to ensure a comfortable old age. As childhood death
continues to fall parents can become increasingly confident that
even fewer children will suffice.
*
Increasing urbanization changes the traditional values placed upon
fertility and the value of children in rural society. Urban living
also raises the cost of dependent children to a nuclear family
(education acts and child labor acts increased dependency through
the late 1800s). People begin to assess more rationally just how
many children they desire or need. Once traditional patterns of
thinking are broken the decline is likely to accelerate.
*
Increasing female literacy and employment lower the uncritical
acceptance of childbearing and motherhood as measures of the
status of women. Valuation of women beyond childbearing and
motherhood becomes important. In addition, as women enter the work
force their life extends beyond the family and the connections
they make with other women serve to break their isolation and
change their attitudes towards the burdens of childbearing. Within
the family they become increasingly influential in childbearing
decisions.
*
Improvements in contraceptive technology help in the second half
of the 20th.C. However, contraceptives were not widely available
in the 19th.C. and likely contributed little to the decline.
Fertility decline is caused by a change in values than by simply
the availability of contraceptives and knowledge of how to use
them. Today in the world there exists a close correspondence
between fertility and contraceptive use, but this likely means
that those families that have chosen to limit family size find
contraceptives the easiest and most effective way to do so.
In the following figure, note that once infant mortality had fallen to
around 70 (which occurred around 1910 in Sweden -- see figure above),
then the fertility rate declines rapidly.

In a similar way, there is a close correspondence between fertility
and infant mortality across the world today:

The age structure of a population entering Stage Three is illustrated
below by using an example from the Third World today:


In Mexico one can see the decline in growth by means of its increasing
impact on the age structure. The youngest base of the population is no
longer expanding.
At some point towards the end of Stage Three the fertility rate falls
to replacement levels. However population growth continues on account
of population momentum. This can be seen in the Mexico example, and it
is responsible for the continued growth in the population of Sweden in
the 1980s. An animation of population momentum in Indonesia can be
viewed HERE.

Demographic Indicators
Birth Rate: 13 per thousand
Total fertility rate: 1.9 births
Natural increase: 0.3% per year 1990-2000
Age structure: 19% under 15 yrs.age
STAGE FOUR is characterized by stability. In this stage the population
age structure has become older:

Demographic Indicators
Birth Rate: 12 per thousand
Total fertility rate: 1.8 births
Natural increase: 0.1% per year 1990-2000
Age structure: 18% under 15 yrs.age
In some cases the fertility rate falls well below replacement and
population decline sets in rapidly:

Demographic Indicators
Birth Rate: 9 per thousand
Total fertility rate: 1.2 births
Natural increase: -0.1% per year 1990-2000
Age structure: 14% under 15 yrs.age
THE TRANSITION IN LESS WELL DEVELOPED COUNTRIES
Mexico and Sweden illustrate the salient differences and similarities
between less and more developed countries.

As do Sweden and Mauritius:

These differences include:
1.
A later (20th.C.) transition in LDCs.
2.
A faster decline in death rates (50 yrs. vs. 150 yrs.). Death
control has been imported from MDCs and applied rapidly. In most
LDCs childhood mortality remains high, but 1/3 to 1/2 what it was
50 years ago. However the most rapid improvements have occurred in
places in which female literacy has increased the most. Therefore,
it is not simply the application of modern drugs that is
responsible but, rather, behavioral changes that have improved
survival (e.g. changes related to hygiene). These types of
behavioral change are readily adopted because, in so far as they
improve survival, they act to support traditional values that
favor life over death in almost all societies.
3.
A relatively longer lag between the decline in death rates and the
decline in birth rates (death rates are lower before decline in
birth rate starts). Fertility change requires a more conscious
effort than mortality change and requires social and behavioral
changes that conflict more with traditional values. This has been
slower coming in LDCs because economic change has been delayed in
many cases. The same economic pressures that existed in urban
areas 100 years ago in MDCs have been slower to develop in LDCs
because many, particularly in Africa, remain very rural. Hence,
attitudes and values have been slower to change.
4.
Higher maximum rates of growth in LDCs: over 3.5% growth per year
at the height of Stage 2 in Mauritius and Mexico, compared to 1.3%
in the same stage in Sweden. Also, therefore, age structures are
far younger in LDCs. These data yield doubling times of 20 years
versus 55 years.
But the greatest similarity concerns the fertility behavior of both
populations (at different times) with respect to infant mortality.
here shown for Brazil, Chile and Sweden:

ANOTHER FORM OF THE TRANSITION
The demographic transition model summarizes change in population
growth over time. Another form of transition exists in the world today
and is associated with the differences in growth rates across
countries of differing wealth. This is implied by the alternative
labels on the traditional transition model (pre Modern,
Urbanizing/Industrializing, etc.).


By using these concepts we can then explain the differences we see in
population growth rates across the world today:

THE IMPACT OF HIV/AIDS IN AFRICA

Sources are:
The Demographic Impact of HIV/AIDS (UN Publication)
The impact of HIV/AIDS in Zimbabwe
AIDS in Africa
Rising Death Rates Slow Population Growth Rates
REALLY USEFUL LINKS
US Census Bureau International Data Base Population Pyramids.
US Census Bureau International Data Base Summary Demographic Data.
US Census Bureau World Population Profile 1998: HTML brief summary;
PDF full version (167 pages).
Population Perspectives (various, contrasting papers on the
"population issue", including Malthus' Essay.)
Global and U.S. National Population Trends
UN Population Division, World Population Trends
Population Policy: Consensus and Challenges (review of policy changes
up to, and through the Cairo Conference: preview of Cairo Conference
available HERE.)
United Nations International Conference on Population and Development
(ICPD), 5-13 September 1994, Cairo, Egypt.
Materials on Population and the Environment.
Materials on Demographics.
GEO 350 (Resource Conservation) links on population
Population policy in India
Africa's Population Challenge
Population Policies for sub-Saharan Africa (World Bank)
The Population Council
News stories: Smaller families to bring big change in Mexico
For one-child policy, China rethinks the iron hand
Special Report on the 1999 UN Conference on Population and Development
*
Birth Control Divides World Population Conference