‘After the Spike: The Risks of Global Depopulation and the Case for People’ by Dean Spears and Michael Geruso

In 1968 a thirty-seven year old biologist working at Stanford University published a short book entitled ‘The Population Bomb’, in which he argued that the level of population growth had reached dangerous proportions and that we were rapidly exceeding the ‘carrying capacity’ of Planet Earth. Famine, water shortages and associated political instability was thus bound to follow as the world’s resources were steadily eroded beyond the point at which they could be replenished.

The book was a huge bestseller in its day, selling over three million copies. It made Ehrlich wealthy as well as a highly sought-after speaker and chat show guest. It was hugely influential, affecting all kinds of environmental debates about the wisdom of economic growth as well as government policy in countries such as India and China where steps were taken to reduce population growth in the final decades of the Twentieth Century.

Rarely can a book have been so widely read, so powerful in its impact and so utterly wrong. Sadly, like one or two others who have been prominent contributors to debates about the near future, Paul Ehrlich lived long enough to see his own predictions (pretty spectacularly) not come true. He died in March 2026 at the ripe old age of ninety-six.

This book by Spears and Geruso, published in 2025, can be read as a very effective reaction against ‘the Population Bomb’ and all the ideas that it has spawned over the past few decades. The real twenty-first century demographic story, according to these authors, is not, in fact one of unsustainable population growth. Quite the opposite. Over the coming decades world population will peak and then start to fall pretty rapidly. Populations in many countries are already falling and this has huge, mainly negative consequences.

The authors identify 2012 as the year in which more babies were born (146 million approx) than in any year in human history, arguing that it is highly unlikely that they will ever again reach that level.

Fertility rates are in freefall across the world, and the consequence is that global population is likely to peak at around 10 billion in the middle of this century (earlier than previously forecast), before falling pretty rapidly – potentially going back down to 2 billion or so over a couple of centuries; a figure we surpassed in the late 1920s. Hence the title ‘after the spike’, the idea being that we have been living through a period of astonishing and historically unprecedented population growth which is a temporary blip and not, as Ehrilch suggested, a long-term, accelerating phenomenon.

I have for many years been fascinated by demographic trends and always find it strange how little serious media coverage of them we tend to see, with the exception, of course, of debates about the level of overseas migration. So I found this book to be absolutely fascinating and would heartily recommend it to everyone.

It starts with a detailed and very compelling statistical analysis demonstrating the notion of a ‘population spike’, setting out its scale and explaining why population decline rather than stability is likely to occur in the near future.

It is essentially a question of falling fertility rates. People are having many fewer children than they used to and this seems to hold true across the world in all industrialised and industrialising economies. We need a fertility rate of 2.1 to sustain stable levels of population (ie; each couple needs to have two children plus a little on average due to child mortality). The global rate is now estimated to be 2.2, down from 4.9 in the 1950s and on a falling trajectory. In most European countries, including the UK the rate is now below 1.5. In South Korea it is just 0.75, meaning that a majority of women are opting not to have any children at all.

Spears and Geruso write very engagingly but also with seriousness and authority. Their core argument is that this coming population decline is something we should be concerned about for all manner of reasons and that steps need to be taken now to try to stabilise global population before it starts to fall precipitately in a few decades time. The central strands are that falling population (and the associated aging that will accompany it) will lead to lower economic growth and hence to reduced human flourishing and wellbeing.

Scientific discovery depends on having more potential innovators; larger populations create bigger networks of collaboration and knowledge exchange; many technologies depend on spreading fixed costs across many users. Thus, a smaller population is likely to mean slower technological progress, fewer breakthroughs and reduced problem-solving capacity. Crucially they argue that this very much includes green technologies and they thus dismiss the view that fewer people will in any way be good for the planet in terms of its impact on climate change.

The authors go on to discuss ways forward, arguing that it is impossible for governments, practically, to incentivise higher birthrates or force higher fertility. Instead the need is for public policy prescriptions that reduce the costs associated with child rearing so that people find it easier to start families sooner and have larger families than they otherwise might intend to.

I enjoyed the book very much and am fascinated by the whole idea that I might very well live to see the population across much of our planet peak, before it starts to fall quite fast. This is a huge issue that is not discussed anything as much as it should be.

I am no expert of course, but I found that Spears and Geruso possibly overstated their case in some respects. First, they are pretty dismissive of the idea that longevity therapeutics might well be invented in the near future which will increase life expectancy considerably, thus reducing the extent and pace of population decline. This is, it seems to me, something that also needs thinking through and considered alongside falling fertility.

Secondly, I think that it is very wrong to consider the environmental impact of population growth purely in terms of climate change. What about physical over-crowding, noise pollution and the necessity of paving over huge swathes of countryside to build infrastructure? These issues are rather avoided in the book.

Finally, of course, there is the promise of AI. Will this not step in to provide us with the kind of ideas and innovation that we are likely to lose as a result of fewer people? In short, my view is that population decline is probably inevitable, not so worrying as is argued here and probably something we can happily adapt to.

Either way I think this is a really important book. Very well-written and thought-provoking. Highly recommended.