For the world, as for his family, the birth of Adnan Nevic was cause for celebration. No less an eminence than the secretary-general of the United Nations attended his arrival, posing with the swaddled child as camera strobes lit a maternity room in central Sarajevo. He was born four minutes past midnight on October 12, 1999, and Kofi Annan had made his way to the hospital like a wise man following a star. There were 5.999999999 billion people on the face of the planet, depending on whose “population clock” you went by. The time had come to designate a six billionth.

The challenges that lay before this infant reflected those of human populations around the globe. His parents, Jasmin and Fatima, were poor. The family lived cheek by jowl in a bleak apartment. His father needed work. Ethnic conflict remained a dormant but ever-present threat to their country. The UN chief offered words of hope, saying this “beautiful boy in a city returning to life should light a path of tolerance and understanding for all people.” But a long and happy life? For that, Adnan Nevic would need a few breaks.

Today, as demographers look ahead to a 10-billion-strong global population, the future of No. 6,000,000,000 is no less clouded. By day, he is an apple-cheeked sixth-grader who loves dogs and cheers on the fabled Spanish soccer team, Real Madrid. At night, he watches over a father stricken by bowel cancer, and sleeps in the same bedroom as his parents in their two-room flat in Visoko, a run-down town 28 km outside Sarajevo. Adnan’s plight could never really stand in for that of all humanity. But it does, to borrow the UN boss’s trope, illuminate the road we will travel over the course of his life.

By 2050, according to the UN’s mid-range estimates, Adnan will count among some 9.3 billion people on the face of the Earth, and 10.1 billion if he lives to see the turn of the next century. Each new addition will pose the same challenges he does. Can we feed, clothe and house them? School them? Provide them with health care and drinkable water? Encoded within these questions are broader ones that speak to our capacity to co-operate, perhaps even to our fate as a species. Will we devise a means to share land and resources? To bring wealth to the planet’s most deprived places? Or will we succumb to the inevitable competition for space and commodities, consigning ourselves to endless wars and humanitarian crises?

In some places, the challenges are so vast as to steal one’s breath. Within two decades, the population of the Democratic Republic of the Congo is expected to balloon to 148.5 million, up from 66 million today. Congo and other poverty-stricken African countries, where fertility rates remain high, will produce much of the world’s future population growth: Germany and Ethiopia now have comparable populations (82 and 83 million people respectively), a UN report notes, but by 2050, Germany’s population is expected to decline to 75 million people, while Ethiopia’s will hit 145 million. It makes the problems of one child in Visoko, Bosnia, look eminently solvable—though even there our best intentions don’t add up to much. Despite brave promises of lifelong financial support at the time of his birth, Adnan’s family now survives on about 250 euros per month. “Had I known back then what I know today, I would never have allowed the UN to declare him the six-billionth person,” Fatima Nevic recently told Maclean’s. “Basically, everyone forgot about us.”

Yet speak to experts whose careers revolve around the population equation, and you’ll also hear notes of surprising optimism—in part because population growth is moderating toward a more manageable pace. With fertility levels slipping in many parts of the world, it will take an estimated 14 years, from 2011 to 2025, for the world to add its eight-billionth person, and another 18 years to add its ninth. Adding number 10 billion won’t happen until 2083, a full 40 years after the nine billionth is born. These forecasts are based on the UN Population Division’s “medium-variant” scenarios, which are considered the most likely to come to pass. The bureau’s highest possible projection puts the world population at an appalling 15.8 billion in 2100, but its lowest would have us at 6.2 billion. That latter figure bears repeating: the human race might actually shrink.

In the meantime, confidence in our capacity to adapt is growing, easing primordial fears about the consequences of unchecked procreation. The debate is increasingly framed by thinkers who view population growth as an expansion of human capital, rather than simply a drain on resources. “Ten billion people is only about one-third more than we already have, and we have plenty of land and activities to occupy them,” says Robert Fogel, Nobel laureate in economics and head of the Center for Population Economics at the University of Chicago’s Booth School of Business. “We’re not going to run out of food, and we won’t run out of factories to employ them. I’m very optimistic that progress will not only continue, but accelerate.”

The cost to the environment remains a key concern, Fogel acknowledges. Global warming, deforestation and the steady extinction of species all speak undeniably to the damage humankind does as it grows. So too does disparity. Countries like Canada and the United States remain disproportionate beneficiaries of human development, while the likes of Somalia and Zimbabwe remain afflicted by misrule, virtually untouched by the transformative forces of women’s education, maternal health programs and contraception. Change must come fast to these places if we are to avert the proliferation of human misery their population curves would suggest. But it will come, say optimists, as surely as it has to parts of the planet once thought impervious to hope.

Last year, Indian entrepreneur Mukesh Ambani and his family moved into the world’s first billion-dollar home. At 27 stories, it boasts a yoga studio, a cinema, and reportedly has an “ice room” with man-made snow flurries to cool off its guests. There are three helipads, and parking spots for 160 vehicles underground. The rooftop offers a view all the way to the Arabian Sea.

The notion of such an extravagant home towering over Mumbai—a city where eight million live in slums—would strike many as crass. But it’s also a sign of the incredible growth India has experienced over the last few decades, a story reflected in the arc of Ambani’s own company, Reliance Industries Ltd., which his father started back in the 1950s; it’s now the largest private sector company in India. At the forefront of the country’s breathtaking economic expansion, observers say, is its demography. India’s population is young and growing: in 2010, the median age in India was about 25, UN figures show (in Canada, the median age last year was 40). In Mumbai, sprawling slums are slowly—and often painfully—making way for strip malls, condos and residential complexes.

This isn’t the traditional portrait of population growth. From 1960 to 2000, the world’s population doubled from three to six billion people, a change that University of Michigan economist David Lam calls “absolutely, historically unprecedented.” Observers were worried we’d run out of resources and room for everybody, yet people are wealthier, healthier and better fed than ever—and it wasn’t just oligarchs like Ambani who benefited. In fact, “the biggest improvements were in the poorest countries, with the exception of Africa,” says Lam, president of the Population Association of America, a professional organization for those who study population issues. In developing regions, the number of people living on less than $1.25 per day dropped from 46 per cent in 1990 to 27 per cent in 2005, according to UN figures. Although the absolute number of hungry people has climbed since 1990 (from 815 million to 925 million) due to population growth, the proportion of them has actually gone down. In the developing world, about one in four children under age five was underweight in 2005, the UN says, down from almost one in three in 1990. And as India’s population more than doubled from 1960 to 2000, Lam says, its food production more than kept up: it tripled.

This did not come as a surprise to academics delving into the relationship between wealth and population enlargement. Every new wave of humanity, reasoned the American economist Julian Simon in 1981, makes more resources available, because “productive and inventive minds help find creative solutions to man’s problems.” Simply put: there are more people with big brains around, hatching ever more ingenious ideas.

Larger populations also mean bigger markets, which allow for mass production and greater specialization of skill. “Consider an assembly line in a car factory,” says Walter Williams, an economics professor at George Mason University in Fairfax County, Va. “You have many individuals, each performing very specialized tasks. If there were only 100 people to buy the cars, why would you do it?” The result, adds Williams, manifests itself at the other end of the production chain, in the form of lower priced goods available to more people. Specialization has proven particularly important in keeping food prices low, as technology and mechanization allow for mass harvesting and processing.

More people speak to the value of big cities, which concentrate labour and talent, while permitting efficient movement of goods and services. The virtues of high population density can seem hard to believe when confronted with the masses of humanity in, say, the shanties around Dhaka. But it is central to the story of Asia’s economic rise. Yes, the number of people living in India’s slums has grown. But so too has the life expectancy of its people, from 44 in 1960 to 66 today. Similarly in China, where cities have been the engine of its three-fold GDP growth over the past decade—so much so that they are draining the countryside of peasant farmers.

What these numbers don’t show is the toll all this activity takes on the planet, and that’s where human-capital theory starts to wobble: our company of 10 billion people won’t be much fun if we’re all living on a barren, overheated planet. If the big brains of the future are half as smart as these economists say, they will weigh the benefit of every new strip mall, coal mine and billion-dollar house against increases in the Earth’s temperature, decimation of farmland, or fish species lost.

Growing up in Colombia, Camilo Mora recalls seeing an ad about population growth on television. “It showed a small aquarium,” he says, “with two fish, then four, then eight, then 16. Eventually, you couldn’t fit any more in there, and it said, ‘Start thinking.’ ” Now a marine biologist at Dalhousie University in Halifax, Mora studies the impact of human population on coral reefs, Earth’s most diverse ecosystems. In a new study, he and colleagues found that a reef’s biomass (its amount of living matter) was directly impacted by human density, since nearby populations bring overfishing, land use and coastal development. It’s potentially very bad news, since 75 per cent of the world’s coral reefs are near human settlements, and 82 per cent of countries with coral reefs are expected to double their populations within the next century.

Scientists believe our planet could be entering its sixth mass extinction—one comparable to the asteroid impact that may have killed off the dinosaurs 65 million years ago—largely propelled by human activity. (A mass extinction occurs when Earth loses more than three-quarters of its species in a geologically short period.) Beyond countless plants and animals that may be wiped off the planet, other resources are under strain. Per capita water consumption is rising twice as fast as the global population, and over the next two decades our need for fresh water will be 40 per cent greater than today’s, the UN predicts. By 2025, two-thirds of the world’s population could be living under water-stressed conditions (when demand can’t be fully satisfied). Dwindling oil reserves have many worried about an impending energy crisis. Climate change threatens to destroy crop yields through drought and storms. With the planet already under such pressure, many question if we can support another three billion people—let alone the nearly seven billion we’ve got.

Over-consumption is a rich-world problem, and the world is getting richer. Canadians consume about 25 tonnes of four important resources (minerals, fossil fuels, ore and biomass) per year, according to a new report from the UN Environment Programme, compared to four tonnes for the average Indian. And one American’s carbon dioxide emissions are equal to those of about 250 Ethiopians. As the standard of living rises in developing countries, people there are also consuming more: humanity is set to eat up three times more resources by 2050, driven largely by increasing population and prosperity, the UN Environment Programme says.

Even given these challenges, Charles Kenny, a development economist in Washington, believes we can sustainably support 10 billion people. “It will take political action and big dollar amounts,” he says, “but amounts we can afford.” Whether governments and voters will agree, though, is another question. The UN’s Intergovernmental Panel on Climate Change recently reported that renewable energy sources—like solar and wind power—could meet as much as 77 per cent of global energy demands by the year 2050, but it will cost $5.1 trillion up to 2020, and another $7.2 trillion from then to 2030.

While Kenny admits he gets “depressed” at the state of global agreements on climate change, there is some precedent for success. The Montreal Protocol, an international treaty signed in 1987 with the aim of reducing the hole in the ozone layer, put controls on the use of ozone-thinning chemicals like chlorofluorocarbons (or CFCs) and has been called a resounding success: experts now say the ozone layer should return to its pre-1980 levels by mid-century (repairing the hole over Antarctica will take a bit longer). Addressing environmental concerns “will get easier as technology improves,” Kenny says, and with some of the world’s greatest minds turned to solving this problem, we might actually be able to figure it out. Whether we’ll have the political and personal will to reconsider energy policy, water use—even our commute to work, or red meat intake—is a more immediately pressing question.

It is a query properly directed at the G20 countries, because the part of the world where the population is growing fastest remains, developmentally speaking, stranded at the roadside. Sub-Saharan Africans use less power, water and food than anyone on Earth, but they’re the first to feel the effects of consumption in other parts of the world. In 2008, for example, while North Americans were complaining about a surge in the price of barbecue steaks—a direct result of growing global demand for grain and energy—families in Mauritania stopped sending their children to school so they could afford to buy bread.

On its face, the band of despair reaching from Benin to Africa’s eastern horn would seem to contradict any theories suggesting that humanity is, in fact, a resource. This region is home to the world’s worst levels of life expectancy, education, disease and poverty, despite runaway fertility rates. A woman in Rwanda has, on average, 6.4 children in her life; in Mali, the rate is even higher (compare that to Canada, where it is below the replacement level of 2.1). Each year, more of these children pour into cities, crowding slums in places like Bulawayo, Kinshasa, or Nairobi. Reducing birth rates would, at first glance, seem a solution to these scenes of despair.

Not so, argue free-market thinkers like Walter Williams, the George Mason University economist. Sub-Saharan Africa might have high birth rates, he points out, but its population per hectare of land is relatively low, suggesting these countries are not overcrowded. What they are is crooked: 16 central African countries rank in the bottom quartile of Transparency International’s most recent annual corruption list—Somalia and Sudan chief among them. As Williams notes, corruption and privation go hand in hand. Development money gets embezzled or stolen. Food shipments get commandeered and sold on black markets. “Africa’s problem is not population growth,” he says. “It’s bad government.”

There are potential remedies to the region’s problems any good politician would try. One is improved farming practices—a long-standing goal of agronomists who have watched in despair as crop yields in African countries stagnated. “We don’t have to do new research to make gains in productivity,” says Ryan Cardwell, a professor of agricultural economics at the University of Manitoba. “There is still a lot of arable land available in some of these countries.” But the proper use of resources to make that happen—from seed stock to chemical fertilizer to irrigation equipment—requires reliable local governments on board with the project.

Another step is investing in education, which would carry the added benefit of pushing down fertility rates. Schooling girls, in particular, leads to sustainable populations, notes Lam, because better-schooled women tend to have fewer children, and invest more in their kids. Yet in 19 African countries, fewer than five per cent of girls finish secondary school. “The 20th century began with very few people completing primary education, and ended with almost everyone doing it,” observes Joel E. Cohen, head of the Laboratory of Populations at Rockefeller University and Columbia University, who notes that some areas of sub-Saharan Africa and South Asia remain the exception. “I believe we will see, by the middle of the next century, a universal acceptance that every child should have a good secondary education, too.” All sorts of societal advantages would flow from this. “Educated people demand a more responsive government,” he says. “They have a better understanding of their bodies, a better capacity for work, and a preference for children of quality, rather than quantity of children.”

It’s the sort of transformation that can take hold when long-held precepts are set aside, when authorities stop treating population growth itself as the root of all evil. If that sounds naive, consider the crisis unfolding in Russia, where—far from enhancing life—population shrinkage has unleashed a cascade of economic and social ills. The country’s population is expected to shrink from 142.9 million people today to 111 million by 2100, with one in five people projected to be over the age of 65 by 2025. With the country’s economic growth in peril, Prime Minister Vladimir Putin has announced plans to invest billions in baby bonuses and health initiatives aimed at boosting the average life expectancy. Yet the obvious remedy of mass immigration remains off the table. The perceived threat to Russian identity has triggered a wave of nationalist xenophobia that has discouraged newcomers and limited the options of political leaders.

Here is where nations like Canada enjoy a huge advantage. This country welcomes more immigrants per capita than any other in the developed world (about 250,000 each year), and our immigration system increasingly targets the world’s best and brightest. We are also comparatively open to the movement of labour, and with some 13 per cent of us expected to be age 80 or older by the year 2100, we will need all of the newcomers we can get. But unlike Russia, we hold the remedy in our hands: we are, and always have been, a country geared to maximize human capital.

For those in less blessed corners of the world, this is a familiar story. Rich countries get richer; the poor trudge on. Our test lies in our capacity to help those whose lives are comprised of equal parts promise and struggle. People like Adnan Nevic, who boasts an 80 per cent average in school, yet lives in a world circumscribed by poverty. Back in 1999, the UN helped find his father a job as boiler operator at Visoko’s main cinema. But Jasmin is now too sick to work. Private “donors” who seized on the occasion of Adnan’s birth to gain a bit of publicity promised money to help buy the family a house—then gave less than half what they pledged. Even with 100 euros per month committed by the City of Sarajevo to celebrate Adnan’s birth, the Nevics can’t afford to enroll him in organized soccer.

Each year on his birthday, friends, family and the occasional government official stop by to wish Adnan happy returns. “They stroke my head,” he tells Maclean’s, “and then they disappear.” This October, the UN Population Fund plans to mark the next billion-person milestone with an international campaign around themes like poverty reduction and educating girls. It will not, however, include the ceremonial designation of a seven-billionth person, say officials, and that’s probably just as well. The measure of humanity, after all, lies not in the number of people we can cram onto the face of the planet, but how we treat the ones already here.