24 October 2005

Doubling time

The World Population Awareness Week (17-23 October) just got over. I bet you didn’t even know. You didn’t even know that such a thing as a World Population Awareness Week exists. After all, nothing much was reported in the media. Nothing much was talked about in other circles either. Where are all those social activists who rave and rant about world population growth?

No matter, let me clear the air a bit. The World Population Awareness Week doesn’t directly deal with issues such as overpopulation or population growth. It focuses on gender inequalities… about the inequalities women face in healthcare, education, employment… about the importance of family planning. After all, the decision to have children is the very essence of freedom.

Attached to this very issue is the matter of human birth and population… the matter of population growth and distribution. If you’ve followed my posts over the last couple of days, you would have read about the concern many sociologists, economists, politicians and heads of states have about the growing population in the world. To put it crudely, there are too many people in this world… and they are multiplying rapidly.

Population grows geometrically (1, 2, 4, 8…), rather than arithmetically (1, 2, 3, 4…), which is why the numbers can increase so quickly.

"A story said to have originated in Persia offers a classic example of exponential growth. It tells of a clever courtier who presented a beautiful chess set to his king and in return asked only that the king give him one grain of rice for the first square, two grains, or double the amount, for the second square, four grains (or double again) for the third, and so forth. The king, not being mathematically inclined, agreed and ordered the rice to be brought from storage. The eighth square required 128 grains, the 12th took more than one pound. Long before reaching the 64th square, every grain of rice in the kingdom had been used. Even today, the total world rice production would not be enough to meet the amount required for the final square of the chessboard. The secret to understanding the arithmetic is that the rate of growth (doubling for each square) applies to an ever-expanding amount of rice, so the number of grains added with each doubling goes up, even though the rate of growth is constant."

Similarly, for population. It works on the principle of doubling time. Doubling time refers to the number of years required for the population of an area to double its present size, given the current rate of population growth. Population doubling time is useful to demonstrate the long-term effect of a growth rate, but should not be used to project population size of a specific area… as several other factors can influence population growth.

[Citation: Population Reference Bureau,
Population Growth]

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