explain briefly demographic transition model ?class 12 geo.. it's again very imp....
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Answer:
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.
Explanation:
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: History of the glacial theory Development of the glacial theory
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 circum