More: Population, Nature, and What Women Want / Edition 1 available in Hardcover
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About the Author
Robert Engelman is Vice President for Programs at the Worldwatch Institute. Formerly Vice President for Research at Population Action International and Founding Secretary of the Society of Environmental Journalists, he has served on the faculty of Yale University. His writing has appeared in Nature,The Washington Post, and The Wall Street Journal.
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Population, Nature, and What Women Want
By Robert Engelman
ISLAND PRESSCopyright © 2008 Robert Engelman
All rights reserved.
Demography is ultimately about sex, but never so much fun in its details.
—Renee Pennington, American anthropologist, "Hunter-gatherer demography"
The street kids called her Condom Sister, but her real name was Henrietta. She seemed a confident seventeen-year-old when I met her a few years ago in Accra, the capital of Ghana in West Africa. During the day she played indoor games with friends and learned about AIDS prevention at a youth center for recent arrivals in the capital, those who had left or lost their families. In the evenings, she worked as a "peer educator," earning about $7.50 a month. That meant trolling the city's streets for young people to talk to, with her anti-AIDS T-shirt, her slogan "if it's not on, it's not in," and her talking points on the virtues of safe sex. Sometimes she carried a few Champions—a brand of condoms manufactured in Dothan, Alabama—to dispense to those who asked.
Despite her street moniker, which I thought might draw some unwanted attention or worse, Henrietta went about her work unmolested. The boys all knew, she told me, "that I control myself sexually." She was abstinent. Henrietta had a dream for herself and planned to stick to it in a choreographed sequence of accomplishments: a job as a hairdresser, marriage, and children one, two, and three—all arriving after she reached age twenty-four. The half dozen other teenage girls I met along with Henrietta at the youth center all expressed the same family-size ideal for themselves. I heard the number three often in Ghana when I asked, as I do on such trips, how many children women wanted to have before their childbearing days were over. In Accra, on that visit at least, the goal was nearly unanimous among young women: three children.
Good, someone who frets about world population growth might think. Three children, after all, is less than the four the typical Ghanaian woman has today and much less than the nearly seven that women there averaged from 1950 to 1975, when the country's population was growing by about 3 percent each year. And if all women waited until age twenty-four to have their first child, that would slow the stream of new arrivals simply by stretching the world's generation gaps. Henrietta and her friends' childbearing ideal was a textbook illustration of a revolution in reproductive behavior that has been occurring in Africa over the last two decades and in the rest of the world for longer than that.
Here's how today's childbearing differs from the past: For most of the last several centuries—and possibly for most of the last 200,000 years—women have had an average of five or more live births each. Today the average is 2.6. It is among the most remarkable behavioral shifts in history.
A common view in the world's wealthier countries is that women in developing countries want to be pregnant much of the time and to mother the ample broods that frequent pregnancy produces. There's no particular evidence that this has ever been the dominant sentiment among women, however, and it's far from the reality today. Fifty years ago, fewer than 30 percent of sexually active women of childbearing age worldwide used contraception or had a partner who was doing so, and women had an average of five children. Today, the comparable figure is above 60 percent, and the average woman gives birth to just two or three children. If contraception were a soft drink, some multinational corporation would be paying its CEO obscenely, but instead it's more a behavior and an attitude than a product, and it has spread all over the world.
But have birthrates fallen far enough? Many people worried about population growth would answer no, Henrietta's ideal family is still too big. For when two parents contribute three children to a population, and those three children grow up to have three of their own, each generation is 50 percent larger than the one that came before. To keep the population steady by only replacing themselves and their partners, women need to have about 2.1 children on average in wealthy countries and somewhat more than that in most poor ones.
Two parents have two children, replacing themselves in a population just fine. Why add the odd fraction of a birth to make "replacement fertility ?" First off, demographers tend to calculate replacement fertility based on the childbearer: the woman. So birthrates are discussed in terms of children born per woman, not per couple. (The monogamous mother, the faithful father till-death-do-them-part, and their two-plus kids form just one among a diversity of family structures. Men can father all the children they please, and demographers, like a lot of other people, generally don't pay much attention.)
Then there's birth itself. For reasons guessed at but not well understood, under natural conditions about 105 boys are born for every 100 girls. The ratio tends to be even higher in first births and with young parents. So, one hundred women need to give birth to about 205 children to ensure that the next generation has the same number of potential childbearers. Already, we have a "twentieth of a child" in the replacement equation.
Then, in any large population, some children die before they grow old enough to have children of their own. You need a few "extra" births per hundred—a little bit in the bank or, as a colleague of mine calls his third child, a "spare"—to hedge against tragedy. If you figure that 1 out of 22 or 23 daughters will not live to see age thirty (roughly the midpoint of reproductive age), replacement fertility settles around 2.1 children per woman. Note, however, that this is the average number of children for all women, not the average for all women actually giving birth. In the United States, 18 percent of women complete their reproductive years without having kids.
If we consider all the women in a population, mothers and nonmoth-ers alike, it's easy to see that replacement fertility is rarely if ever a steady, stately 2.1 children per woman. Given differences in sex ratios at birth (influenced in some Asian countries by sex-selective abortion) and child survival rates, different populations require different numbers of children per woman to replace the parents' generation. In western Europe and Japan, where deaths of young people are quite rare, the replacement fertility rate may be as low as 2.06 children per woman. In the United States, the rate is a small fraction higher, 2.08, because young people in the States are a bit more likely to die before parenting than in most wealthy industrialized countries. But this variation from the lowest rate is minor compared to the 2.9 replacement fertility rate of Africa or the 2.7 rate of the world's least developed countries. Obscure as the statistics are, replacement fertility rates quantify the failure to survive among the youngest and most vulnerable among us. We ought to be tracking how the rates change, but no one does.
Watching Children Die
Through much of human history, replacement fertility may have been as high as five, six, or even more, a grisly guess based on the fact that modern married women tend to have about this number of children when they aren't using contraception. (Some have many more. A small religious group known as the Hutterites was renowned for having a documented fertility from 1880 to 1950 of roughly ten children per woman. But that's unusually high fertility, well above that of any country in known history.)
During much of the two thousand centuries since Homo sapiens became a separate species, population growth rates remained low. As we'll see, our numbers jumped dramatically at key moments, but there were also periods of abrupt decline, and yet others of relative stasis. Some women in the deep past may have had some success in managing their own fertility, but it was likely high mortality, not low birthrates, that was the greatest check on growth. Throughout prehistory, women may well have watched half of their children die, needing to give birth six or more times just to keep the population from fading away.
Even today, having at least some three-child families is essential to survival of the species. The two-child ideal—once marketed by the population-movement slogan "Stop at two"—would condemn us to extinction if it really did become universal for long. Why? Suppose only a few young people die in your population, and the sex ratio at birth holds at the normal 105 boys for every 100 girls. Even under these ideal conditions, replacement fertility will always be just slightly above two children per woman. (Any 100 women will need to have from 205 to 210 babies to be confident they'll have 100 daughters who grow up to have children themselves.) Babies arrive, however, only in whole numbers. So if all women had precisely two children each, they wouldn't quite be replacing themselves and their partners. Then, add in the many women who have just one child or none at all. Such women make demographic room for others who have three, four, or a dozen children in populations that are nonetheless, on average, at or below replacement fertility. Without occasional above-replacement fertility, populations begin a long, dangerous slide. If you're the parent of three children and worry about population growth, you can take comfort in the fact that someone has to have three. It may as well be you.
There's an obvious corollary, however, to this celebration of the third child: if average fertility rates remain well above two live births per woman, death rates will eventually rise to levels any sane person would call catastrophic. Exponential growth cannot continue indefinitely on the finite surface of a planet. Not long ago, UN demographers calculated the population density of the world under the seemingly modest scenario that the average number of births per woman would remain at the current 2.6. In less than three centuries, this "constant-fertility" scenario would produce 134 trillion people on earth, pushing them onto every patch of terra firma from deserts to mountaintops at a density 143 times that of Hong Kong today.
People who think about population often dream up these sorts of thought experiments to make tangible such intangibles, whether they're trying to prove human numbers are a problem or a nonissue. A favorite factoid for the nonissue side is that all of today's world population could fit into the state of Texas, with room for a house and a modest eighth-of-an-acre yard for households of five people each. They're right, though no one seems to have asked Texans how they feel about this idea. The more important point is that once settled in the Lone Star state, the world's billions would quickly die of thirst unless they could somehow move the mouth of the Amazon River to Galveston. Eating red meat or even an un-Texan vegan diet would be out of the question.
Like all things in the physical universe, natural resources like water and soil can only go so far. The same is true even of the inventions and other innovations—more efficient engines, more productive varieties of food crops—that make resources useful to people. No one really knows any more than you do what the "limits to growth" might be for human numbers. You're free to pick 10 billion, a trillion, or some other "illion" that no one can relate to. But once humanity reaches that limiting range, whatever it may be, average fertility had better be low enough to stop or reverse growth. Otherwise, rising death rates will do the job without mercy.
"Limits to growth" hasn't been a very popular idea since a book with that title brought the scorn of economists and cornucopian thinkers in the 1970s. But the idea that such constraints are out there is coming back. There's not enough water for those alive today in the Horn of Africa, not enough atmosphere for those alive on earth to use fossil fuels the way we do in the United States. In Afghanistan and more than a dozen countries in sub-Saharan Africa, ill health, hunger, and violence make youth as risky a phase of life today as it was in Charles Dickens's London. Parents need to have more than three children per woman to replace themselves in such populations, since infants have only a two-thirds probability of making it to age thirty.
While it's too simplistic to blame rapid population growth for the high death rates in these countries, overcrowding is likely one of several interacting factors. Parents in Rwanda and Malawi, for example, divide their subsistence farms between so many sons that each tiny plot can barely support a family. Many in the younger generations look for alternative livelihoods, but these aren't easy to find in either country. Malawi suffers from recurrent famine, and more than one in three newborns fails to make it to mid-reproductive age. And some see the 1994 genocidal war of Rwanda as an example of what can happen when population densities reach intolerable levels in countries that lack decent government and decent economic options for their citizens.
Even when birthrates hit the critical replacement value, whatever it is in a specific population, it takes time for human numbers to stabilize. Population change has its own momentum, like that of a speeding truck that skids along the pavement after the driver slams on the brakes. If most parents are members of a "youth bulge" in the population—maybe they're baby boomers—then even if they average 2.1 children per couple the sum of all people will keep growing. Only a small group of older people is leaving the population—not to put too fine a point on it, they'redying to leave it—while a big, bawling, baby-boom "echo" is being born, comparable in number to their parents. Until deaths equal births, with the generations of reproducers about equal in size to those dying, the beat of growth goes on.
Population momentum can also work in reverse, to keep shrinking populations from stabilizing even when couples are replacing themselves precisely. In a population weighted toward old people, the two children of a small generation of young parents may not be able to compensate for the large number of elderly dying. Demographers didn't pay much attention to this until they realized that some European populations could begin having more than two children per woman tomorrow—Germany, Italy, and Spain, for example—and still their populations would keep declining for decades to come because of this negative momentum.
Some writers fear that below-replacement fertility—any level too low to replace parents in a population—amounts to a sentence of demographic self-extinction, as in "Will the last Italian please turn out the lights?" Actually, below-replacement fertility has been nearly as common in human experience as above-replacement fertility. For our species, obviously, family size too small to keep population from shrinking has never been fatal and, except for some small groups, it rarely has lasted long enough to threaten survival. (European invasion and disease overwhelmed the Caribs in the Caribbean Sea and the aboriginal Tasmanians south of Australia. Such disappearances of small subpopulations were no doubt common in prehistory and early historic times.) Most countries today with fertility rates below replacement are still growing demographically, generally due to still-young populations or net immigration or both; although, among the dozen countries with the smallest families, population stability or decline is indeed the rule. Moreover, it's inaccurate to say that birthrates in low-fertility countries are in any kind of free fall. Most countries that have reached 1.1 births per woman have experienced leveling and even slight rises in fertility, suggesting that 1.1 births may be something of a fertility floor.
To be sustainable, then, a population will need some, but not too many three-child families. Human numbers are staggeringly sensitive to small differences in fertility. Two or three thousand years with 1.8 children per woman, and vines start to snake up vacant skyscrapers and break the windows. The same few millennia with 2.4 children per woman, and people are stacked up on each other's heads. Such sensitivity to small differences in fertility is one reason demographic trends and data merit attention. However you feel about population as an issue, whether the earth holds 5 billion or 15 billion people in 2100 will have an awful lot do with the how rapidly and dangerously the global climate warms, the survival of anything we can call wild, and much more besides.
Right now this many people live in a place called Planet Earth: 6,633,975,438. Oops. It went up. But seriously, you really don't want to consult this book, or any other, if you want to know the latest figures about national or world population. Demographers, someone once said, are accountants, but without the charisma. Demography itself, however, is endlessly dynamic. So a new book on population shares this with a new baby: it's only new until the next one arrives. In 1993 George Will, a columnist meticulous about numbers related to politics or baseball, wrote this sentence : "There are about 4 billion people alive now, and all will die more or less on a known schedule." World population at the time was just shy of 5.6 billion. We can reliably guess that the demographic reference Will pulled from his shelf was copyrighted around 1974.
Excerpted from More by Robert Engelman. Copyright © 2008 Robert Engelman. Excerpted by permission of ISLAND PRESS.
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Table of Contents
Preface Introduction: Uncrowding Eden Chapter 1. Henrietta's Ideal Chapter 2. The Population Growers Chapter 3. Outbound Chapter 4. The Grandmother of Invention Chapter 5. A Sense of Timing Chapter 6. Axial Age Chapter 7. Punishing Eve Chapter 8. Age of Enlightenment Chapter 9. Zen and the Art of Population Maintenance Chapter 10. The Return of Nature Notes Bibliography Index