The rapid growth of human population is mainly as a result of rising food supply. Beginning of agriculture and domestication of animals marked the first step of mankind towards a civilized society. During the period from birth of Christ to 1800 AD there was refinement in agricultural technology and the rising human population was limited by expansion of agriculture over the forested land.
On the other hand, the population was limited by high mortality rate due to famine, diseases and wars from 18th century onwards immunization, antibodies and insecticides eased the presence of heavy mortality. Life expectancy has been increased during the current century which has resulted in a spectacular rise in human population during 20th century.
As per estimate population growth predicts a population of 8.2 billion in the year 2025 AD and more than 10 billion by 2025 AD.
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The exponential growth of human population in certain countries including India does not mean that resources are unlimited. It is the remarkable advances made in medicine and technology which have brought down human death rate to greater extent.
A habitat cannot support any population beyond a certain limit. If the population goes beyond that limit resource limited shows it a adverse effects on the population by increasing death rates and decreasing birth rates, which eventually will lead to a decline in population density. The maximum number of individuals of population that its environment can support and sustain is called the carrying capacity.
As the population increases in size, there will be more competition for the available space and food which in turn will affect population growth.
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When the population increases in such a way that increases in the fixed proportion of its own size at any time, its growth is said to be exponential. The number of children born in a population will normally increase proportionally with the number of people, or size of the population. Thus, population grows exponentially. As the size becomes bigger, the increase also becomes larger. Thus, the actual increase will depend on 1) rate of increase in proportion to its size and 2) its own size at the time.
The population growth rates vary from nation to nation, some nation show very high growth rates above 3 per cent. On the other hand some nations are not growing at all and few have declining population.
In America, the growth rate is about 2.5% as compared to 1 per cent in the developed countries. Their differences are important in terms of the population added per year. The population growth of the developed nations of Europe and North America are characterized as follows:
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(1) Along with other nations, they have long history of very slow growth over thousand of year during which time the birth rate and the death rate must be approximately equal.
(2) The death rates decreased due to better sanitation and health care.
(3) Within a few decades, their birth rate also began to decline resulting in a decrease in the rate of population growth. Such a decrease, first in the death rates resulting in increased growth rate.
On the other hand, the less developed countries did not begin to benefit from better health care sanitation until after the Second World War. Since then the death rates have sharply declined but their rates have not decreased. Accordingly the growth rates have increased to above 2% and 3% in some cases.