The ecology of man and trend of growth of human population can be studied at the following three levels: primitive man, agricultural man and industrial man.
It is believed that the population of our ancestors, the hominoid apes or Australopithecus and relatives, a few million years ago, were confined to Africa and total number of individuals was 125,000 only.
During man’s evolutionary history, the size and Functioning of human brain has increased considerably. (The Australopithecus had small brain with an average’ volume of only about 450 to 600cubic centimeters). Larger brains in turn increased the potential store of cultural information and resulted in self- reinforcing and coupling of the growth of culture and brain size.
This trend continued until perhaps 100,000 to 35,000 years ago, when growth of brain size stabilised at an average of some 1500 cubic centimeters and man constituted the modern species, the Homo sapiens.
For a hundred thousand generations, our ancestors lived in small, isolated, nomadiac groups as hunters and food-gatherers, spacing themselves according to the availability of wild food. The numbers of people in these scattered foraging bonds probably grew slowly, if at all. Around 30,000 B.C. mankind has spread (emigrated) from Africa to every other part of this earth. Around 9000 years ago, the total human population was low, usually estimated as less than 20 million.
Ecologically, man’s primitive position in natural communities was that of a particularly large, vicious land animal with an unusually wide range of food. He was and still is omnivorous structurally, physiologically and psychologically. In other words, he was a consumer, a primary consumer as well as a secondary or tertiary consumer.
It does not mean that man could eat literally everything, but that he could eat almost any kind of animal food and any kind of concentrated plant food, especially fruits, seeds and tubers or starchy roots biological consequences of this breadth of adaptation were that man could find food in almost any of the endlessly diverse natural communities of the earth and that in each community his status was complex.
He became part of almost all food chains that could include a large animal. In fact, as long as man remained in this stage of cultural development, he was just another member of the complex food-web of the community and populations soon reached some maximal population levels in balance with the rest of the community.
All his energy requirements were furnished by the renewable resources in other words, by plants or animals that are “renewed” each year by biological growth, when primitive man began to use fire; his fuel was wood from trees that were renewed.
Sometime between 7000 B.C. and the old kingdom of Egypt (which began perhaps about 5500 B.C.) certain groups of primitive man began modifying their environments by cultivating specific kinds of plants (especially grains) and domesticating food animals’.
Ecologically speaking, this was accomplished by shifting the relative numbers of individuals of -various species in the food web. Agricultural man further shifted the balance of nature in the original biotic communities by killing any wild herbivores that fed on his cultivated plants and killing carnivores that preyed on him and his domestic animals.
During this agricultural revolution, a sedentary way of life evolved, which allowed the construction of permanent dwellings in which man could seek shelter from the weather. As life became safer and the food supply more stable, a large number of babies survived around 8000 B.C., the world population is estimated to be about 5 million.
By the time Egypt became well established as an ancient civilization (perhaps about 4000, B.C.) the world population probably reached the 100 million levels. By 1650 A.D., human population had climbed to 453 million. The average rate of increase during this period (7000 B.C. to 1650 A.D.) was about 50,000 per year.
As human population continued to increase, man continued to modify his environment in such a way as to permit even greater population-size. With the invention of the wheel, transportation devices were developed and utilized for moving food from place to Place, thus allowing for larger concentration of people in a given place.
The discovery and utilisation of non-renewable resources, such as the various metals and the fossil fuel sources permitted human population to increase beyond the limits originally imposed by the balance of nature.
The so-called Indus- trial revolution saw the development of tools and machines that resulted in the construction of more and better housing, the production of more and better food items and textiles, and the development of food storage, preservation and transportation techniques.
Simultaneous acquisition of knowledge and development of drugs and techniques permitted medical science to greatly reduce mortality rates and the agricultural sciences to produce more and better food from cultivated plants and domestic animals.
During this period human population has increased at a rate that has become alarming to many people. By 1830, the population had reached one billion; by 1930, two billion; and by 1961, three billion.
Between 1650 and 1830, the rate of increase was just over three million per year; between 1830 and 1930, about ten million per year; and between 1930 and 1961, about 30 million per year.
In recent years, total population has been increasing at an ever-increasing rate and is apparently in a logarithmic phase of population increase. The current rate of increase is about 55 million per year; about 150,000 per day; 6300 per hour; or 100 per minute. Remember, this is net increase—total births less total deaths.
If current birth rates and death rates are maintained, human population will reach six billion by 2025 A.D. It is estimated that a human population of only 1 billion people is the maximum supportable at U.S. levels of affluence by present agricultural and industrial resources (Kendeigh, 1974).
The much larger populations now occurring are possible only because over 80 per cent of the world population is living well below these levels. These under- privilege people seek a larger share of the world’s resources and a rise in their standard of living. The option is either ruthless suppression which is unthinkable or accommodation which is applied by present Governments in the form of family planning measures.