In developing the new edition of Man Swarm with renowned conservationist Dave Foreman, I learned so much. For example, I used to think that if birth rates decline it must mean population growth is slowing. But as the book discusses, there’s a lot more to the picture. Here are three important factors that are too often overlooked:
Percentage Rate versus Absolute Increase of Growth
It is critical to look at both percentage rates of growth and absolute increases. From Man Swarm, “Say that the percentage rate of growth slows from 2.1 percent to 1.7 percent a year over a few years while the absolute increase of yearly growth goes from sixty-four million to seventy-nine million to ninety-three million in that time. How can this be? Because there are more women giving birth at the lower rate.”
Age Structure
As Foreman explains, “Another way to look at population is by population age structure. Even if there is a drop in a nation’s growth rate, its population still rises for many years. Why? As big segments of the population go through their childbearing years, they have many, many children. In 1995, one-third of Earth’s population (two billion) was under fifteen years of age, while only about five percent of it (three hundred million people) was over sixty-five. The youngsters are making far more babies now than the number of oldsters that are dying; therefore, the population is growing.”
“Latest population numbers show lopsided percentages under fifteen years old. With such a landslide of youngsters coming into their childbearing years, even if we reduce birth rates to the replacement level of 2.1 children per woman, it will take two or three generations, or fifty to seventy-five years, before the population stabilizes.”
Longevity
“J. Kenneth Smail, Professor Emeritus of Anthropology at Kenyon College, speaks to another piece of the puzzle that’s mostly overlooked. ‘Ongoing global gains in human longevity will continue to make a major contribution to world population expansion over the next half-century, regardless of whatever progress might be made in reducing fertility’…In other words, how longevity grows population is a big deal.”
To add to these three is this Paul Ehrlich quote: “[T]he world’s population will continue to grow as long as the birth rate exceeds the death rate; it’s as simple as that.”
Want to track population growth? Bookmark the U.S. Census Population Clock. Watch one birth every X seconds, one death every X seconds, one net international migrant every X seconds and how many seconds it takes for a “net gain” of one person – the day this posted that net gain in the U.S. was one person every 14 seconds.
Now that is population growth. Don’t let birth rate declines fool you. Just three hundred years ago, in the U.S. we were six hundred ten million. We are adding more than that every ten years. As Foreman sums it, “Human population has exploded gruesomely in the last two hundred years. And it will keep shooting up for some time.”
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