At first glance, looking at the numbers does little to bolster Musk’s argument. A thousand years ago, there were only around 320 million people on the planet. Then, 300 years or so ago, our numbers exploded. In just a century from 1700, global population almost doubled, from 600 million to 1 billion. No wonder Thomas Malthus, that demographer célèbre, issued his most famous warning of population catastrophe in 1798, just as mankind reached the billion mark. Yet that warning was swept aside by the sheer scale of change. In the two centuries since, we have increased more than sevenfold, to the estimated 7.7 billion of us on the planet today.

And we’re not stopping yet. According to UN figures, global population growth isn’t forecast to flatten until the end of this century, by which time there are projected to be almost 11 billion of us on the planet.

But importantly, this picture is very uneven. Asia will reach its tipping point half a century earlier, in 2050, and lose more than half a billion people in the rest of the century. In South America the picture is the same. Swathes of Europe, too, will soon see not so much a population boom as a population bust.

Take Romania, population just under 20 million today, forecast to collapse to 12 million by 2100. Or Italy: 60 million today, only 40 million in 2100. These are dramatic changes. Birth rates in developed countries are commonly already far below the 2.1 children per mother replacement rate. America’s fell to 1.86 children in 2006 (though it has recovered slightly since). In Britain, according to the ONS, “The total fertility rate for England and Wales in 2020 fell to 1.58 children per woman, the lowest since records began in 1938.” Worldwide we are hitting what the celebrated data analyst Hans Rosling famously called “peak child”. It is a trend accelerated by the pandemic, as parents have put off having children until better times. That is a familiar historic occurrence. Bad news – from recessions to climate change – hits birth rates.

Musk considers this to be a wrongheaded heaping of woe upon woe. In his mind, good times – economic growth, spreading prosperity, scientific, medical and technological advance of the kind whose Western-world ubiquity, in the memorable phrase of novelist Tom Wolfe, enabled “the average burglar-alarm repairman [to live] a life that would have made the Sun King blink” – have all been accompanied by population growth.

“Population collapse is a much bigger problem than people realise,” he tweeted earlier this year. Not least, perhaps, because the conventional wisdom of those UN forecasts was challenged last year by an influential study, published in The Lancet, suggesting that the world’s population will actually peak in 2064, far earlier than expected, and have declined by 2100 to 8.8 billion, 2 billion fewer than usually thought. “The societal, economic, and geopolitical power implications of our predictions are substantial,” noted researcher Professor Stein Emil Vollset at the time. “In particular, our findings suggest that the decline in the numbers of working-age adults alone will reduce GDP growth rates that could result in major shifts in global economic power by the century’s end.”