The unevenness in the distribution of world population may be attributed to the following factors:
(i) Availability of arable land and water.
(ii) Age of civilization.
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(iii) Accessibility of places.
(iv) Restrictions of national boundaries.
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(i) Arable Land:
There is a close relationship between the arable land and the concentration of population. The plain areas having fertile soils and suitable climate (temperature and rainfall) for the cultivation of crops are the regions of high density of population.
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Still about 50 per cent of the world population is dependent on agriculture for their livelihood. Consequently, the areas of intensive agriculture have high density of population.
However, it is not only the plain areas where agriculture is possible, because man through his efforts has developed agriculture on terraces on mountain sides (e.g., Angami tribe near Kohima in Nagaland), heating greenhouses in cold climates (e.g., Netherlands, Germany, France, Denmark, Russia, Norway, Sweden, etc.), and irrigating deserts (e.g., Nile Valley, Turkmenistan, Ganganagar, Jaisalmer and Bikaner districts of Rajasthan, India etc.).
Nevertheless, a comparison of the distribution of arable areas and population reveals several similarities. In the great plains of India and the eastern plains of China, there are high densities of population. Same is the case with some parts of Nile, Tigris, Euphrates, Syr and Amu valleys, where irrigation allows farming in what is climatically a desert.
(ii) Age of Civilization:
The second most important factor which influences the growth, density and concentration of population is the age of civilization. Generally, the longer a place is continuously used by farmers, the dense and large is the population.
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For example, the Eastern China plains and the Indo-Gangetic plains have long history of intensive agriculture and they have high densities of population. Contrary to this, the plains of Mississippi in USA, Pampas of Argentina, down grasslands of Australia and New Zealand and Velds of South Africa, though equally productive, the cultivation was started only after the 17th century. Consequently, these areas are relatively sparsely populated.
(iii) Accessibility:
Accessibility of places and regions is also a very important determinant of population growth and its distribution. In the agriculturally less productive but industrially advanced societies, the people are dependent on secondary and tertiary sectors and most of the industries have been located at places which are easily accessible.
Accessible places are those which are easily connected by transportation to many other places. The factor of accessibility is most important in an economy based on manufacturing and trading.
The economic advantages of locations like Kolkata, Mumbai, Delhi, Chennai, Karachi, Rotterdam, London, Chicago, Paris, Rome, Beijing, Shanghai, Alexandria, Djakarta, Aden, Lagos, Singapore, Lahore, Dhaka and Tokyo create employment opportunities that attract large populations.
These centers of dense population grow by both natural demographic increase and producing the markets that generate even more economic opportunities for additional population. Consequently, these agglomerations where people have been engaged in industrial activities for several generations (e.g., Western Europe) tend to be densely populated.
(iv) Restrictions of National Boundaries:
Each country has its own international boundaries. Crossing of these boundaries by the people of one country to another country is not allowed by the proviso of international law.
Owing to this restriction, the people of overpopulated countries cannot enter the developed countries with less density of population. For example, Bangladesh has a large population density while Australia, Canada and USA have low density of population.
In the absence of restrictions of national boundaries, the population from countries like China, India, Pakistan, Indonesia and Bangladesh could have migrated to USA, Canada and Australia to earn a better living.
Such international migration is very limited, mainly because most nations do not allow a mass influx of new immigrants.
Countries like Australia, Brazil, Canada, Russia, USA, New Zealand, etc., have enormous resource potential and they do not allow immigrants unless they are technically and educationally outstanding. In other words, political restriction to international migration of people is an important factor which helps explain the existing distributional pattern of world population.
Although major migrations have altered the pattern of the world’s population in the past, such movements have been drastically curtailed in recent decades. Most governments restrict immigration, and several countries control emigration as well.
According to The World Guide (11th edition, 2007), the population of the world has crossed the mark of 6 billion in October 1999, but what is more significant in relation to future food production is the rate of population growth that has characterized the post-1950 and which forms the basis for the exploration of global and inter-regional population growth rate into the 21st century.
It may be seen that population growth rate has increased dramatically since 1950, doubling in just 43 years which is in contrast to the previous doubling period of population during the prehistoric period.
The growth rate of population even between 1850 and 1950 was much slower (Table 3.2). These trends are startling, and while they reflect increased life expectancy and improved health care, they also demonstrate increase in pressure that has been brought to bear on earth resources and the food producing system.
The growth trend of population has beeniIt indicates that the most significant population increase has been in the developing nations where about 75 per cent of the world’s population is now concentrated.
Although global population growth rates are gradually declining and in many nations, especially in the developed world, they have undergone a demographic transition from a state of growth to one population equilibrium, there are still many developing countries where population growth rates are in excess of 3 per cent per annum.
Most of these countries are in Africa in which populations are expected to be doubled in about 30 years
Elsewhere in the developing world, population growth rates are declining; in South America, the declines have been small, while in China the population growth has been halved in the last decade (1991-2000). The life expectancy is about 40 years in Sierra Leone, whereas in Guinea and Gambia it is 41 years each.
There are also striking variations in the population composition of the developing and developed world. According to the UNO’s estimated population figures of 2010, in the developed countries, only 20 per cent of the population is in the under 15 age group and 18 to 20 per cent in the over 65 age group, while in the developing countries 32 to 46 per cent of the population is under the age of 15 and about 8 per cent is aged over 60 years
Thus, improving health care, coupled with high fertility rates and a large proportion of people entering their reproductive years, provide an inbuilt momentum for future high population growth even if fertility rates decline.
The birth and death rates of population (1775-2010) have been shown in it may be observed from this that the birth and death rates in the developing countries are declining fast after the Second World War, while in the developed countries both are significantly low.
There are 19 countries in Europe in which more than 17 per cent of the total population is over 65 years of age and only about 20 per cent is around or below 15 years of age.
These are: Austria, Belgium, Bulgaria, Croatia, Denmark, Finland, France, Germany, Greece, Hungary, Italy, Latvia, Norway, Portugal, Spain, Sweden, Switzerland, Ukraine and the United Kingdom. The infant mortality rate is also very low in developed countries.