I suspect that, during the dramatic news of coronavirus, few people lingered long over two recent stories. One was the report from the Red Cross that a fresh refugee and migrant crisis is building up, with long-term demographic pressures augmented by the economic distress and destitution caused by Covid-19 as it reaches the poorest people in the poorest countries. The second was an analysis of population trends, published in Lancet, predicting an implosion of numbers later this century and a marked ageing in Europe and Asia offset by many more, and younger, Africans.

In my formative years, in the 50s and 60s, the conventional wisdom was that we faced the grim prospect of a population explosion or time bomb detonated by irresistible exponential growth. The planet was fast running out of resources and food supplies would be outstripped by unsustainable demand. The dismal theories of economist Thomas Malthus were rehabilitated and given modern flavouring by the emerging environmental movement. Mass starvation could only be avoided by restrictive population policy, centring on birth control.

Some countries took these warnings seriously including Maos China with its extreme "one child" policy and, briefly, India where, under Indira Gandhis emergency, there was a campaign of mass sterilisation, not all voluntary (as also in China).

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But the history of countries which developed economically shows that the idea of populations exploding indefinitely is absurd: rather, there was a demographic transition as countries progressed from high birth and death rates to low birth and death rates via a period of continued high birth rates and low death rates.

The key factors in shortening the transition was the empowerment of women through education, and reducing child mortality. Once people thought their children had a good chance of survival, the perceived necessity to have several was reduced. This has happened even in parts of the world like Bangladesh and much of India. There has been enormous progress in development, especially in the two decades around the turn of the century, reflected in the success, until recently, in meeting the UNs Millennium Development Goals.

So, how have we got from paranoia about explosions to potential implosions? The recently publicised study suggests the planets population will peak at 9.7bn in 2064 (from 7.6bn today), so we are unlikely to experience loneliness any time soon. But by the end of the century it is predicted that some countries already experiencing population decline like Japan, Spain and Italy will have more than halved their population. China will join them as members of the less than 50 per cent club, and the population they have left will be very old.

More mainstream forecasts have the global population peaking later. But the key insight of the Lancet study is that something new is happening many societies in Europe and Asia are no longer replacing their population from one generation to the next. Female empowerment, leading to the enjoyment of worthwhile careers, is clearly a factor. So is the sheer practical difficulty of raising children in environments where the cost and availability of childcare and housing are prohibitive and jobs are precarious. Added to those is a minority but growing belief that having one child or no children contributes to saving the planet.

Even if there is some rebalancing back to larger families it is unlikely to change the fundamental conundrum of the rich world (including China), which is growing numbers of economically inactive and medically dependent older people, supported by a shrinking working population.

By contrast, the population of sub-Saharan Africa is set to treble by the end of the century. The Lancet study suggests that Nigeria will have grown to 791m people by 2100, surpassing China whose population will have shrunk to 732 million.

The army of people identified by the Red Cross as hovering on the north coast of Africa in desperate circumstances, and hoping to make a new life in Europe, is surely set to grow. They are only too anxious to give developed countries the benefit of their labour, while Western governments have been equally anxious to keep them out. A question at the heart of the identity politics which drives tough immigration policy is whether richer countries want in the long run to be ethnically diverse, youthful, and productive, or homogeneous and geriatric.

The part of the world which will find this dilemma most difficult is Asia. Japanese and Chinese societies, in particular, have a strong sense of racial identity and exclusiveness. Immigration is still a lesser issue and where it is permitted, mostly kept well out of sight (as in the Singaporean dormitories which have incubated Covid-19 with such ease). Japan appears to have consciously opted for planned senescence, and all Chinas muscle-flexing as the worlds new superpower wont conceal its fate. Both are set to be old before their time.

The US is better placed. An open, if ugly, debate about its long-term future is underway. The last two American presidents one the son of an African immigrant, the other a white nativist represent two scenarios facing the country. Trumps imaginary wall is probably the nearest he and his followers will really get to stemming the tide of diversity. Whatever the outcome of Novembers election, the US economy cannot withstand a real and prolonged closure of its borders.

In Western Europe, too, the border is permeable, like the leaky boats which try to breach it. A key turning point was German chancellor Angela Merkels decision to admit one million Syrian refugees. At the time it was damned with faint praise as courageous but foolish; now that the arrivals are being methodically, and apparently successfully, integrated the initiative seems to be a hallmark of modern Germanys strength, self-confidence and optimism.

In its weird and eccentric way, even Britain may yet follow the same script. I took Brexit to be a conscious decision to turn our backs not just on Europe but on the world. It was all about immigration, and we didnt want any more. Now, I am not so sure. Since the convulsion of the EU referendum, immigration has been mentioned by far fewer people in Ipsos MORI polls about the most important issues facing the nation. This peaked at 56 per cent in September 2015 but had fallen to 13 per cent by November 2019.

Perhaps the governments welcome for Hong Kong Chinese will prove sincere. Maybe they will open the door to South Asians and Africans who are rich in points under the new immigration system. This approach to immigration has everything to do with economic pragmatism, and nothing to do with humanitarianism. It wont help many of the people in leaky boats on the Mediterranean. But at least it leaves the door half-open to a rejuvenated population.

Read more:

The refugee and migrant crisis is getting worse. Our approach has to change if we want everyone to thrive - The Independent