Human population is an important element of the terrestrial environment. Man is probably the latest occupant of the earth, as his evolution took place less than two million years ago. In the early periods, human beings were like other animals at the mercy of the natural environment. He depended on food gathering, hunting and fishing. A large area of land was needed to support a small family. He had to lead a nomadic life. His food habits, clothing and shelter were influenced by the local environment.
The ability to make tools of stone and metals and use them for hunting improved his skill in getting food. The development of shifting cultivation and later settled agricultural in the river valleys improved his feed supply. Assured food supply meant better health and longevity. Population increased gradually. Forests and grassland could be cleared by setting fire to them or by cutting them with his iron axe. With the use of coal, oil and other mechanical sources of energy, productivity increased. Improvement in sanitation and public health reduced death rate. Thus man was no longer at the mercy of the environment.
His activities started having an impact on the environment. Pressure of population on the land increased. People started immigrating to new continents such as the America, Australia and New Zealand. With increasing population, the activities of man started having adverse impact on the environment.
Development in transport and communication led to greater exchange of commodities between nations. This made possible supply of food grains and raw materials to tide over shortages in some parts of world.
The role of man in production and consumption of resources is significant. The number of human beings in any area gives us a broad idea of the nature and extent of economic activities in that area. The rate at which man utilizes his basic resources is also determined by the distribution of human beings on this earth. Human resources are the most precious of all resources.
Developing nations are unable to improve their standard of living partly because they lack skilled manpower for development of their resources. Absolute number of people living in a country has little meaning. The needs and aspirations of people and their consumption levels vary. The per capita consumption of food, fuel, minerals and other products is much greater in countries like the United States than India.
Developing nations of Africa do not produce adequate food to feed the population. They cannot afford to purchase food at high cost from other countries. Thus it is necessary to study not only the distribution of population in the world but also the composition of population, in terms of urbanization, languages, religions, cultures and quality of life. It is also necessary to study the human impact on the environment so as to reduce the adverse features and ensure a certain minimum levels of living to the present population of the world but also for the future generations as well.
Men from the olden times made efforts to count their numbers and thus take a census of their population. But there was a large margin of error in their censuses because of undeveloped techniques of enumeration. Modern census enumerations of reliance were undertaken in 18th and 19th centuries in countries of western Europe and North America. As time passed, the margin of error in the census enumeration also was considerably reduced.
Due to the strenuous efforts made by the United Nations Organization, techniques of census enumeration have been improved considerably since World War II in a number of countries. However, due to illiteracy and lack of communications in some underdeveloped countries guesses and not accurate figures are taken in census.