 |
| Human Population Growth |
Since the Industrial Revolution of the nineteenth century, human populations have experienced a period of explosive growth. Overpopulation now poses a real threat to plant lives, ecosystems, and the long-term sustainability of the earth’s current ecological balance.
Just eleven thousand years ago, there were only about five million humans who lived on the planet Earth. The initial population growth was slow, largely because of the way humans lived—by hunting. Such a mobile lifestyle limited the size of families for practical reasons.
When simple means of birth control, often abstention from sex, failed, a woman would elect abortion or, more commonly, infanticide to limit her family size. Furthermore, a high mortality rate among the very young, the old, the ill, and the disabled acted as a natural barrier to rapid population growth.
    |
Thus, it took more than one million years for the world’s population to reach one billion. The second billion was added in about one hundred years, the third billion in fifty years, the fourth in fifteen years, and the fifth billion in twelve years. When humans became sedentary, some limits on the family size were lifted. With the development families by helping with farming and other chores.
By the beginning of the common era (1 CE ), human population had grown to about 130 million, distributed all over the earth. By 1650, the world population had reached 500 million. The process of industrialization had begun, bringing about profound changes in the lives of humans and their interactions with the natural world.
With improved living standards, lower death rates, and prolonged life expectancies, human population grew exponentially. By 1999, there were about 6 billion people, compared with 2.5 billion in 1950. By 2002, the world population was well on its way to 7 billion, with an annual growth rate of nearly 100 million.
Plants, Agriculture, and Human Population
Starting about eleven thousand years ago (five million people), humans began to cultivate such of agriculture, children became an asset to their plants as barley, lentils, wheat, and peas in the Middle East—an area that extends from Lebanon and Syria in the northwest eastward through Iraq to Iran.
In cultivating and caring for these crops, early farmers changed the characteristics of these plants, making them higher yielding, more nutritious, and easier to harvest. Agriculture spread and first reached Europe by approximately six thousand years ago.
      |
Agriculture might also have originated independently in Africa in one or more centers. Many crops were domesticated there, including yams, okra, coffee, and cotton.
In Asia, agriculture based on staples such as rice and soybeans and many other crops such as citrus, mangos, taro, and bananas was developed. Agriculture was developed independently in the New World. It began as early as nine thousand years ago in Mexico and Peru.
Christopher Columbus and his followers found many new crops to bring back to the Old World, including corn, kidney beans, lima beans, tomatoes, tobacco, chili peppers, potatoes, sweet potatoes, pumpkins and squashes, avocados, cacao, and the major cultivated species of cotton.
For the last five to six centuries, important staple crops have been cultivated throughout the world. Wheat, rice, and corn, which provide 60 percent of the calories people consume, are cultivated wherever they will grow. Other crops, including spices and herbs, have also been brought under cultivation.
The growing population has changed the landscape, distribution, and diversity of plants dramatically. Clear-cutting and deforestation have driven many species (both plant and animal) to extinction.
Relatively little has been done to develop agricultural practices suitable for tropical regions. As a result, the tropics are being devastated ecologically, with an estimated 20 percent of the world’s species likely to be lost by the mid-twenty-first century.
A Threat to Sustainability
Without effective measures of control, the human population could exceed the earth’s carrying capacity. Humans are, at present, estimated to consume about 40 percent of the total net products generated via photosynthesis by plants.
Human activities have reduced the productivity of earth’s forests and grasslands by 12 percent. Each year, millions of acres of once-productive land are turned into desert through overgrazing and deforestation, especially in developing countries.
Due to over fertilization and aggressive practices in agriculture, loss of topsoil occurs at an annual rate of 24 billion metric tons. Collectively, these practices caused the destruction of 40 million acres of rain forest each year during the 1960’s and 1970’s and the extinction of enormous numbers of species.
Through technological innovation and aggressive practices in agriculture, a 2.6-fold increase in world grain production has been achieved since 1950. However, this increase in food output is not nearly enough to feed the population.
Based upon an estimate by the World Bank and the Food and Agriculture Organization of the United Nations, one out of every five people is living in absolute poverty, unable to obtain food, shelter, or clothing dependably. About one out of every ten people receives less than 80 percent of the daily caloric intake recommended by the United Nations.
In countries such as Bangladesh and Haiti and in regions such as East Africa, humans are dying in increasing numbers because of the lack of food. This lack of food may stem from drought, soil depletion, or soil loss; more often, famine results from inequitable distribution of resources among populations.
Situations exacerbated by a growing population also pose threats to the environment, aggravating the problems of acid rains, toxic and hazardous wastes, water shortages, topsoil erosion, ozone layer punctuation, greenhouse effects and groundwater contamination.
