The year of six billion Math of population Problematic projections Unsatisfied demand Was Malthus right? 
Produce. Reproduce
First off, the population of an area depends on births, deaths and the number of people moving in or out. If you were as simpleminded as we Why Filers, you'd figure that was it. But statisticians don't like to add  they greatly prefer sophisticated math, and rely on percentages rather than absolute numbers to express population growth. Conclusion? The math gets kinda complicated kinda fast, professor. We'll spare you the gruesome details, but just remember that the rate of increase depends on the number of children per woman, and on the length of generations  her age at the first baby. Thus, says Donald Waller, a University of WisconsinMadison professor of biology and ecology, if all women had three kids with a 15year average generation time, the rate of population growth would be 2.7 percent. If the average spacing were 30 years, the growth would drop in half  to 1.35 percent. Waller notes that exponential growth (compound interest to economists) is characteristic of living organisms. One bacterium divides into two, which make four, then 8, 16, and pretty soon you have a whole lakeful of bacteria. It's the same with people, except, as Waller notes, we're a species that has the capacity to see into the future, and to plan for our children's welfare.
Doubling time
How do these factors translate into population predictions?

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