Population Growth and Control (Human)

The numbers of humans on Earth have increased enormously during the past several millennia, but especially during the past two centuries. By the end of the twentieth century, the global population of humans was 6.0 billion. That figure is twice the population of 1960, a mere 30 years earlier. Moreover, the human population is growing at about 1.5% annually, equivalent to an additional 89 million people per year. The United Nations Population Fund estimates that there will likely be about nine billion people alive in the year 2050.

In addition, the numbers of animals that live in a domestic mutualism with humans have also risen. These companion species must be supported by the biosphere along with their human patrons, and can be considered an important component of the environmental impact of the human enterprise. The large domestic animals include about 1.7 billion sheep and goats, 1.3 billion cows, and 0.3 billion horses, camels, and water buffalo. Humans are also accompanied by a huge population of smaller animals, including 10-11 billion chickens and other fowl.

The biological history of Homo sapiens extends more than one million years. For almost all of that history, a relatively small population was engaged in a subsistence lifestyle, involving the hunting of wild animals and the gathering of edible plants. The global population during those times was about a million people. However, the discoveries of crude tools, weapons, and hunting and gathering techniques allowed prehistoric humans to become increasingly more effective in exploiting their environment, which allowed increases in population to occur. About ten thousand years ago, people discovered primitive agriculture through the domestication of a few plant and animal species, and ways of cultivating them to achieve greater yields of food. These early agricultural technologies and their associated socio-cultural systems allowed an increase in the carrying capacity of the environment for humans and their domesticated species. This resulted in steady population growth because primitive agricultural systems could support more people than a hunting and gathering lifestyle.

Further increases in Earth's carrying capacity for the human population were achieved through additional technological discoveries that improved capabilities for controlling and exploiting the environment. These included the discovery of the properties of metals and their alloys, which allowed the manufacturing of superior tools and weapons, and the inventions of the wheel and ships, which permitted the transportation of large amounts of goods. At the same time, further increases in agricultural yields were achieved by advances in the domestication and genetic modification of useful plants and animals, and the discovery of improved methods of cultivation. Due to innovations, the growth of the human population grew from about 300 million people in the year A.D. 1 to 500 million in A.D 1650.

Around that time, the rate of population growth increased significantly, and continues into the present. The relatively recent and rapid growth of the human population occurred for several reasons. The discovery of better technologies for sanitation and medicine has been especially important, because of the resulting decreases in death rates. This allowed populations to increase rapidly, because of continuing high birth rates. There have also been great advances in technologies for the extraction of resources, manufacturing of goods, agricultural production, transportation, and communications, all of which have increased the carrying capacity of the environment for people. Consequently, the number of humans increased to one billion in 1850, two billion in 1930, four billion in 1975, five billion in 1987, and six billion in 1999. This rapid increase in the population has been labeled the "population explosion." While there are clear signs that the rate of population increase is slowing, estimates show the number of humans on the planet to be nine billion in 2050.

Because the populations of humans and large domestic animals have become so big, some predict severe environmental damage caused by pollution and overly intense use of natural resources. If this were to happen, the carrying capacity for the human population would decrease, and famines could occur. A controversial movement in the latter years of the twentieth century for "zero population growth" advocates the widespread use of birth control, in order to maintain the birth rate at equal numbers to the death rate.