Intense shift.Some researchers argue that popu- As world population surges, debate surrounds studies suggesting that population growth can have economic and environmental benefits IN 1937, A BUREAUCRAT SERVING IN THE British Empire’s Kenya Colony penned an alarming memo to his bosses about conditions in the Machakos Reserve, a hilly, drought-prone farming region 50 kilometers south of Nairobi. “Benevolent British rule” had encouraged the explosive “multiplication” of the “natives,” he reported, leading to massive environmental degradation. “Every phase of misuse of land is vividly and poignantly displayed in this Reserve, the inhabitants of which are rapidly drifting to a state of hopeless and miserable poverty and their land to a parching desert of rocks, stones and sand.” The apocalyptic warning came as the region’s population approached 250,000. Today, more than 1.5 million people call Machakos home. Rather than a cautionary example of the perils of overpopulation, however, for some experts Machakos has become a symbol of something very different: the idea that rapid human population growth, even in some of Earth’s driest, most challenging environments, is not necessarily a recipe for disaster—and can even bring benefits. They argue that, over the past 75 years, population growth in Machakos 544 bers alone don’t determine the consequences of population growth, and that a complex mix of culture, socioeconomics, and biology also plays a role. The findings are also renewing interest in the work of a pioneering Danish economist who challenged conventional notions about the dire consequences of more people—and are raising hopes that even the poorest, fastest-growing regions could, with the right mix of policies, ride out the global population tsunami. Along with this cautious optimism, however, come profound doubts. Some experts wonder whether the “Machakos miracle” can be replicated elsewhere or sustained in regions experiencing unprecedented population growth. “Although local successes offer hope, it is dangerous to generalize,” warns Jules Siedenberg of the University of East Anglia in Norwich, U.K. “We need to be sure we are drawing the right lessons, since people’s lives are at stake.” Doomsters and boomsters The question of whether population growth poses a dire threat or a potential opportunity is an old one. Not long after Thomas Robert and nearby Nairobi has triggered social and Malthus made his now-famous 1798 preeconomic shifts that have made it possible for diction that more people would doom us to residents to regreen once-barren hillsides, “gigantic inevitable famine,” an opposing reinvigorate failing soils, reduce birth rates, camp of population “boomsters” emerged, and increase crop production and incomes. highlighting the potential benefits of repro“A landscape that was once declared good duction. More people, they argued, meant for nothing is now like a garden when the more labor, technological innovation, and rain falls,” says Michael Mortimore, a geo- economic growth. Ever since, the rhetorigrapher with Drylands Research, a United cal doomster-versus-boomster battle lines Kingdom–based nonprofit have barely shifted: Today, organization, who helped Video featuring author for instance, even as many David Malakoff. document the turnaround experts warn that more peowww.scim.ag/nY4t8K in More People, Less Erople threaten to exacerbate sion, a 1994 study that is still hunger, poverty, and enviinfluential—and controversial—today. “Too ronmental problems, others respond by notmany people still have the simplistic notion ing that nations with some the world’s highthat too many people is a problem,” he says. est population densities—such as Singapore “What happened in Machakos challenges and the Netherlands—also have some of the that pessimism.” world’s strongest economies and environAnd Machakos isn’t alone. In other hard- mental commitments. pressed regions, researchers are finding that One recurring flashpoint in the debate even explosive population growth can be has been the ultimate impact of population accompanied by some surprising trends— growth in the world’s “drylands,” the driest such as increased tree cover, more produc- and often poorest farming areas of Africa, tive farms and economies, and improved Asia, and Latin America. They hold nearly well-being. Such results are adding new fuel one-third of Earth’s people, and some of these to long-standing arguments that sheer num- populations, especially in Africa, are grow- 29 JULY 2011 VOL 333 SCIENCE www.sciencemag.org Published by AAAS Downloaded from www.sciencemag.org on September 12, 2011 Are More People Necessarily a Problem? lation growth made possible land use and farm productivity improvements in Kenya’s Machakos region. CREDIT: GETTY IMAGES/DORLING KINDERSLEY NEWS ” to lower birth rates. Less Erosion. capitalhave been able to weed a field just once during a range of studies. see some hope for conclusions into a detailed. This provided So. In 1994. ship. as its population authors argued. secting what had transpired in Machakos incentives for farmers. given the right ers built terraces to control erosion. It examined the tion density has had positive history of subsistence farmeffects. as one bottom line: More People. Meanwhile.at the time. the Boserup’s work carried some provoca. Erosion has become an important—and conincentives. the study tions of Agricultural Growth: “controverted” Malthus and The Economics of Agrarbacked Boserup. could be counted on to invest in stepped up their use of animal fertilizers. the in a speech. had helped create demand weren’t just mouths to feed but for the farm products grown also brains that could think and hands and legs Malthus controverted? in Machakos and also seasonal jobs for that could work very hard. Others. was a bar. who spent icy world with a storm. they noted in a 1994 follow-up paper might not have a fixed “carrying capacity”. “Machakos is not unique.org SCIENCE VOL 333 29 JULY 2011 Published by AAAS Downloaded from www. In 1965.” tive implications. What’s more. however. Critics. have 545 . field surveys of everything from restoration miracles despite growing poputrary to the conventional wisdom. her work sug. Many see crisis looming World War II brought new in those numbers for people ideas back home.between 1930 and 1990. with more labor.” In Machakos. to spend 2 years dis. natural resource damage. in ger harvests from less land. infortion”: the use of new technolomation-sharing. published a Mortimore a major award in slim volume titled The Condi2008. hailing a promising trend of beautiful theory destined to be destroyed by church and community groups. Drawing on a trove of Other places in Kenya. farmNearly 2 decades later. By the 1990s (bottom). Politiincreasing yields and maybe even providing opment Institute and Francis Gichuki of the cians had helped out by mostly getting out of the income needed to dig an irrigation ditch or University of Nairobi.ers documented how.CREDITS (TOP TO BOTTOM): KENYA NATIONAL ARCHIVE. the then-littleThe book “hit the polknown Boserup. dry areas soil fertility to household finances.’s Oversees Devel.dren and invest more in education. Rising populations had Boserup suggested it could also created a rich social naturally trigger “intensificamilieu for innovation. more trees.” Mortimore says. solving. Mary Tiffen of the U. they might be the demographic and socioeconomic forces message. and lations.org on September 12. more people “The idea was that people race and revegetate hillsides that were barren and eroded in the 1930s (top). such questions prompted the young people from the region.the way and letting markets create the right haul in animal manure to restore soil fertility. In particular. “very out of step able to sustain more people over time and that had buffeted Machakos households with the doom and gloom about population thus hasten the “demographic transition” and how they responded. and political gies and more labor to get biginvolvement. source of their optimism. the impact “more people. Rebirth. a transition to more sustainnuanced. They also exam. for example. One was that “under. and communities in population.K. extra labor had enabled Machakos farmers to ter. the researchers distilled their however. Less gested that dryland farmers. more ing and offered a theory that people had provided both essentially turned Malthus the labor and the “necessity” upside down. many were skeptical: Was this another ined the growing influence of women. kets in nearby Nairobi. and the environment. 2011 ing rapidly at 2% to 3% per men who went off to fight in year. It was a instead. counterintuitive mist who died in 1999. concludian Change under Populaing that “increasing population Pressure. Instead of risfor a transition to intensificaing population density leading tion and better land stewardto barren fields and starvation.sciencemag.” not overpopulation. Another was that. tentious—scholarly classic. con. for instance. and often provocaable livelihoods and cite Ester tive 300-page compendium Boserup. the and take care of their land. Recently.sciencemag.data—including historical documents and Nigeria and Indonesia. Finally. MICHAEL MORTIMORE SPECIALSECTION www. More People. Greater economic the growing season could now justify using enabled a large team led by Mortimore and stability also led families to have fewer chilmore abundant labor to weed it three times. a farmer who once might World Bank and other institutions to launch Machakos with income for further. and less erosion” ugly facts? of the end of colonialism. In the 1990s. and how local in some drylands.with desertification paid homage to the study Still.” the most of her career consultAssociation of American ing for international developGeographers noted in giving ment institutions. had also experienced rier to development.roughly quadrupled. including the one that intensive improvements. The research. rather and began selling food to burgeoning mar.head of the United Nations agency that deals than aggravating. Mortimore says.photos. numerous interviews—the team charted in the journal World Development.nearby Nairobi. a Danish econowith a bold. or downplayed some issues. “The dynamics play out have shown that in the Sahel.546 29 JULY 2011 VOL 333 SCIENCE www. tives.Fruits of labor. a Malawi experience. meanwhile. Santa Barbara. “Local ‘win-win’ outcomes tion growth—and in the nation’s growing –DAVID MALAKOFF are clearly possible. believes it is a mistake to assume reported in a 2009 study in Population that the Boserupian processes seen and Development. less migrating to clear new farms in forerosion: The twentieth century in ested areas. studies that “tease out the effects” is that there are countless instances of changing demographics in remote where fast-growing farming comforest frontiers. Conservationoutlook remains at best unclear. Machakos markets are now a source of produce for found that a farmer’s age. Studies by have provided a one-time economic jolt. Some farmers lack the market affect his or her willingness to put demand created by a nearby city.” which appears to and some technical assistance. meanwhile. are careful. can result.” ipe for success. They have tion densities have responded by both titles such as “Fewer people. with older others lack access to capital. gender. Carr’s team a 2006 critique in Development Polargues.with fast-growing populations. taught him improvements. ists. and ple. fertilizers. And. Understanding such nuances ple take-home messages. for one. And the poorest says Erle Ellis of the University of Mary. many scholars are devel. the agricultural “extensisouthern Bolivia. Baltimore County. and land tenure. location. like realtors. to the debate over whether MachaDepending on local circumstances.sciencemag.” he cautions. they say one key fac. and conclusions and argued that it ignored At the same time. experts say. And many drylands experts is easier. some location. Maybe the book could the needs and knowledge of local people. There’s have favored families that already some evidence that the extra greenery had land and other assets.org Published by AAAS Downloaded from www.oping a view of population impacts that Machakos-like “regreening” of arid areas fee-planting boom in the 1970s that may fuses Malthusian and Boserupian perspec.” he argued in What’s needed now. More Deforestation.” team led by David Carr of the UniEast Anglia’s Seidenburg. .” itly recognizes the downside of popula. The population densities can have much study showed “solid outcomes” higher deforestation rates than those for one region but has perpetuated with higher densities. like ‘farmers will that “Boserup was right. David Malakoff is a writer living in Alexandria. it will open a new chapter in the long believe that more people need not mean catas. kos is an exception or the rule in a families faced with growing populastring of technical papers.” and “More peofication” predicted by Malthus. for instance. His own studies in capital and labor into the land.geographer Chris Reij of the University of Although overall incomes are up and birth tor in predicting consequences is location. “People are working If so. or China of areas that have been farmed for male farmers sometimes deciding to forgo information. And Carr the barriers that often prevent scaling-up ultimately urbanization. which has led to the and his colleagues predict that new studies local successes.But the trend “doesn’t necessarily mean life sity leading to agricultural intensification.thousands of years.sciencemag. environmental problems. versity of California. The problem. more soil degradation: The intensified land use à la Boserup.’ distracts from addressing supported extensive population growth and and land-use policies. Mortimore says. researchers have like biodiversity loss and water polfound both Malthusian and Boserulution.” Intensification has could help forge better forest-protection figure it out.harder than ever. Amsterdam in the Netherlands and others rates are now down in Machakos.” Siedenburg says.” as Boserup predicted. and when and where more addresses local conditions and recognizes coercive one-child policy—which implic.lands (a process experts call “land release”).org on September 12.be titled Less People.researchers are documenting a notable. British is helping to make poor farm commuscholar John Murton concluded in a nities more resilient to droughts and 1999 study published in The Geoeconomic setbacks. a Boserupian “orthodoxy of population dentiques and agrees that there is no single rec.” abandonment and revegetation of less fertile “will surely test” what they say has become Mortimore sees merit in some of the cri. such as a cof. such as giving farmers ownfamilies may not have benef ited ership of trees that grow on their land from the “miracle. for instance. Paradoxically. he says.policy changes.people are a problem. but the long-term graphical Journal. whereas land. Virginia. “The trick is getting good policy that the specter of Malthus looms over China’s affects the planet. the in Machakos are “an automatic result is that areas with relatively low result” of population growth. Other research has munities have not been innova. 2011 CREDIT: DUNCAN WILLETS/ALLSTAR PICTURE LIBRARY/NEWSCOM raised questions about the study’s methods New synthesis In some parts of Africa. Machakos-like icy Review. tive enough and are suffering as a nearby Nairobi and surrounding areas. depending on where you are. And and rich debate over how population growth trophe. Researchers have also added pian forces at work in deforestation. He fears that “focusing on sim. note that intensifiIn the forest frontiers of South and cation can actually worsen problems Central America. the tree. “unhelpful hyperbole.and experts note that it still doesn’t grow enough differently.” shrub-growing trend has been boosted by food to feed its population.