When Besse Cooper was born in Tennessee in 1896, there were fewer than 2 billion people in the world. When she passed 100 years old, there were not yet 6 billion. Now, as the world's oldest person, she shares the Earth with 7 billion fellow humans.
This latest landmark has brought a resurgence of the usual hand-wringing about global overpopulation - and the attendant stress on supplies of food, clean water, energy, the prospect of wars and pandemics, and the dangers of climate change. By 2050, the world may hold 9 billion people.
Paul Ehrlich, the author of the 1968 bestseller "The Population Bomb", made a series of striking predictions: that the population was outrunning global food supplies; that hundreds of millions of people would starve to death in the 1970s; that the oceans would be devoid of life by 1979 due to DDT poisoning; and that the US population would plunge to 23 million by 1999 amid a wave of cancers caused by pesticides.
Remarkably, Ehrlich still enjoys respect as an authority on population. Interviewed by the UK's Guardian newspaper as the 7 billion landmark approaches, he opined that there was only a 10 per cent chance of avoiding the collapse of global civilisation.
Although poverty, deprivation and inequality remain all too prevalent, and despite the strain of recent food price increases, long-term trends are all towards a healthier, wealthier, better-fed world.
Sadly for the preachers of "resource wars", the incidence of war and violence has decreased, unevenly but unmistakably, over the past 100 years. More than half of India's population lived in poverty in the early 1970s; now barely a quarter do.
Literacy rates increased in every region of the world over the past two decades, with particularly fast progress in Africa and south and east Asia. Although the 850 million undernourished people around the world are still too many, as a share of global population it is half the level of the early 1970s.
The challenge of meeting the needs of growing economies in developing countries is significant. But it is not insuperable. Studies suggest that a global population of 8 billion to 10 billion by 2050 can be fed, even taking into account richer, more meat-heavy diets.
Improvements in agricultural yields have slowed, but so has population growth. With better fertilisers and crop varieties, African food output could triple, as Asia and Latin America's did from 1960 onwards.
We are not on an unsustainable path of exponential growth. Instead, the world needs one more big push to feed its people over the difficult next half-century.
After that, population growth is likely to level off, and a new challenge will dominate - that of ageing.
In 1960, Iranian women bore on average 6.9 children. Now they have only 1.6, below replacement fertility levels. This demographic transition to lower birth rates is almost universal, even in poorer countries such as Bangladesh, Nigeria and the Philippines.
The proponents of population control counter by arguing that increasing consumption per person, and a growing global population, are two components of the same problem.
But the global economy by mid-century might be six times bigger than it is today, while the number of people increases by only 40 per cent or so. Clearly, growing consumption is by far a bigger strain on the global environment than population.
To give some sense of the disproportionate environmental impact of different people: the average American consumes the calorie equivalent of almost 8 Big Macs daily, 2.4 times the intake of an Eritrean. Europe is twice as densely populated as Africa. An Australian emits 13 and a half times more carbon dioxide than his or her Indian counterpart.
These fashionable fears of over-population have undercurrents of xenophobia and misanthropy. Western commentators fret about countries where population is supposedly rising fast - Africa, India and Muslim societies.
Britain's anti-immigrant BNP party worries about "soaring world population". The BBC commentator Susan Blackmore said: "For the planet's sake, I hope we have bird flu or some other thing that will reduce the population, because otherwise we're doomed," comments worryingly reminiscent of the advocates of mass slaughter to create a new civilisation, such as Mao or Pol Pot.
The solution is not "Fortress Europe", coercion, China's "one-child" policy, forced sterilisations or explicit targets for population shrinkage. Instead, people need access to reliable contraception and family planning advice. Women require improvements in education and the freedom to make their own choices about pregnancy.
Social safety nets remove the need for large families to provide for the parents' old age. International migration should be liberalised, and made more rational and humane. Agriculture can be both more productive, more efficient and less damaging to the environment.
Human beings are not just machines for eating and emitting carbon dioxide. Somewhere among the healthier, wealthier, better-educated 9 billion or 10 billion people of the 21st century are the new Marie Curie, Rumi, Akbar, Confucius and Nelson Mandela.
Robin M Mills is an energy economist based in Dubai and author of The Myth of the Oil Crisis and Capturing Carbon.