How many people can planet Earth support? That is the thorny question that economist Partha Dasgupta tackles in Time and the Generations. Or, as he asks: “How should we evaluate the ethics of procreation, especially the environmental consequences of reproductive decisions on future generations, in a resource-constrained world?” Given that I have previously called overpopulation the elephant in the room that few wish to address, my interest was immediately piqued.

Time and the Generations: Population Ethics for a Diminishing Planet, written by Partha Dasgupta, published by Columbia University Press in June 2019 (hardback, 320 pages)

Intuitively, the answer to this question to me has always seemed: it depends. The IPAT equation formulated in the 1970s by Barry Commoner, Paul R. Ehrlich, and John Holdren is pretty clear about it, Impact = Population × Affluence × Technology. There is not going to be a single number, it depends on what we consider a good life. The more affluent we want our lifestyle to be, the fewer of us there can be before we require more natural resources than our planet can supply. This is the essence behind concepts such as Earth Overshoot Day and humanity’s global ecological footprint. These consider renewable natural resources such as timber, clean water, and fertile soil (but, it should be pointed out, ignore resources such as fossil fuels and ores that are essentially non-renewable).

So, superficially, this question does not seem like rocket science. But Dasgupta here turns it into something very much akin to rocket science. If your idea of stimulating dinnertime conversation includes the ideas of philosophers and economists such as Henry Sidgwick, John Rawls, Derek Parfit, or Frank Ramsey, with a healthy dollop of normative ethics, utilitarianism, and axiology, then this book will go down well. If the above means nothing to you, then, like me, you might struggle with this book. Dasgupta writes for an audience of fellow philosophers and economists here and takes as a given a certain level of background knowledge and familiarity with the vocabulary. Below I will try to demystify some of this and hopefully not butcher it too much in the process.

“Given that our planet has resource constraints, what level of economic activity can it support long term? And can we deduce an optimum population size from this?”

This book is part of the Kenneth J. Arrow Lecture Series, which honours the intellectual legacy of this economist. Dasgupta has revised and expanded on material from this and other lectures and turned it into a large essay, the Arrow Lecture, that sits at the heart of this book. It is driven by two questions. Given that our planet has resource constraints, what level of economic activity can it support long term? And can we deduce an optimum population size from this? To answer these questions, Dasgupta engages in a formal mathematical modelling exercise in both normative and population ethics. Normative ethics studies ethical action: how should one act, morally speaking? Population ethics studies the ethical problems that arise when our actions affect who and how many of us are born in the future.

As his starting point, Dasgupta takes Henry Sidgwick’s version of utilitarian thought. As an ethical theory, utilitarianism says that we should act to maximize happiness and well-being for individuals involved. When applied in the context of population ethics, I think this means asking how we can maximize well-being for humanity as a whole. Dasgupta starts with a model of a timeless world in which goods are produced and consumed and asks what level of population maximizes well-being (so-called total utilitarianism). He then modifies this theory to construct what he calls generation-relative utilitarianism. He adds a component of time in the form of existing people choosing how many children to have and asks how we can maximize well-being in that scenario. The aim of this whole exercise? A model that offers potential parents a normative theory of, and ethical guidance on, reproductive decisions.

The Arrow Lecture is accompanied by other material that, fortunately, is quite enlightening. I would even go so far as to recommend you read it first to get a better handle on the book’s outline. There is a foreword by economist Robert M. Solow, some emails from Kenneth J. Arrow to Dasgupta on the Lecture, three commentaries from economists Scott Barrett, Eric Maskin, and Joseph Stiglitz – with a response by Dasgupta, an epilogue, and a reprint of a closely-allied paper co-authored with his daughter Aisha Dasgupta. To make it self-contained, the last part of the Lecture actually borrows heavily from this paper, so there is a fair bit of overlap here.

“[Dasgupta’s] model [gives] some very rough numbers for optimal population size, with most estimates falling somewhere between 1.5 to 3.5 billion people.”

Where the modelling exercise was rather abstruse to me, the second half is where things get really interesting. He first offers the briefest of reviews of humanity’s impact on the planet, stressing repeatedly just how insanely fast, just mere decades, we have increased our standard of living and, with it, extraction of natural resources. Then he applies his model to get some very rough numbers for optimal population size, with most estimates falling somewhere between 1.5 to 3.5 billion people. This agrees with earlier work by Paul Ehrlich and co-authors, as well as the recent limit of 3 billion championed by Christopher Tucker.

Dasgupta is frank about the model simplifications made up to this point and the crudeness of some the estimates of our impact on the biosphere. But, as he points out, “What matters […] is not the exact figure but whether the footprint exceeds 1. On that there should be little question” (p. 105). Indeed, and for a fuller picture I refer readers to Vaclav Smil’s Harvesting the Biosphere, the recent Humans versus Nature, and my review of Cataclysms. The same hockey stick patternhockey stick shape that characterises the graph of atmospheric carbon dioxide concentration against time shows up in a broad class of other geochemical signatures. This is why stratigraphers are trying to get the term Anthropocene formally recognized. This pressure on the biosphere is also feeding into what is now widely called the sixth mass extinction (notably, Dasgupta was co-editor on Biological Extinction, published in the same year as this book).

There are three other things that Dasgupta writes worth mentioning here. First is his invocation of the economic concept of externalities. These are positive or negative consequences that our actions have for others that are not accounted for. An example of a negative externality is global warming caused by the burning of fossil fuels. We, its consumers, are not paying the cost of global warming which is instead inflicted on both existing and future people. Dasgupta argues this applies just as much for reproduction: adding another human being to an already overburdened planet has costs for all future people. For most, life is so sacrosanct that nobody wants to discuss this, and applying this kind of cold calculus is still taboo. High time somebody broached that topic.

“[…] the Sustainable Development Goals laid out by the United Nations […] are silent on population and the burden increased affluence will have on the planet.”

Second is that the Sustainable Development Goals laid out by the United Nations, which aim for example to reduce global wealth inequality, are silent on population and the burden increased affluence will have on the planet. One more reason why this conversation is so terribly overdue. Third – there is good news too – preferences for the number of children people wish to have is, what Dasgupta calls, socially embedded. It is subject to both people’s desire to compete with one another and to conform to a majority. Changing such preferences might be less costly than it first appears, though it will be none the easier for it.

One thing Dasgupta, by his own admission, stops short of is formulating policies as to how we could achieve optimum global population. Luckily, others are starting to be willing to discuss this. Equally important will be the tough discussion on how we can change our behaviour so as to live lighter on our environment, something I cover in my review of Planetary Accounting.

Time and the Generations takes no prisoners where its level is concerned, being primarily written for an audience versed in economics and philosophy. Though I struggled to get to grips with parts of the book, I found it refreshing and uplifting to see an economist champion something else than endless growth.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Time and the Generations hardback or ebook

Other recommended books mentioned in this review:

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“Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes“, written by Nathan H. Lents, published in Europe by Weidenfeld & Nicolson in May 2018 (hardback, 233 pages)

Anatomical quirks such as the above are probably the ones we are all most familiar with. As mentioned in my recent review of Eyes to See: The Astonishing Variety of Vision in Nature, eyes have independently evolved multiple times and nature offers different solutions for capturing light. Why, then, do the photoreceptors in our eyes face backwards, with the big bundle of nerves exiting the eyeball creating a blind spot? Cephalopods seem to have their eyes wired in a more logical way. You might also have heard of the recurrent laryngeal nerve that innervates our larynx. Rather than running from the brain straight to our voicebox, this nerve takes a circuitous route, looping around our aorta. In long-necked species such as giraffes this means metres of unnecessary nerve!

The answer, as any evolutionary biologist will tell you, is that these faults reveal much about how we evolved from our distant ancestors. Neil Shubin also discussed this in his marvellous book Your Inner Fish: The Amazing Discovery of Our 375-Million-Year-Old Ancestor. That nerve I mentioned? When we were still fish it innervated the gills, the evolutionary precursor of our larynx. With no neck to speak of, the brain, heart, and gills in a fish lie on a more or less straight line and there was no problem with the route this nerve ended up taking. However, once fish evolved into creatures with necks, it started to look a bit dumb. But alas, evolution cannot throw everything out and start from scratch, it has to work with whatever (faulty) material is at hand.

“[…] once fish evolved into creatures with necks, [the laryngeal nerve] started to look a bit dumb.”

And these kinds of bugs and quirks abound. Next to anatomy, Lents covers our dietary needs and our inability to synthesize vitamins that many other organisms make themselves. Our DNA is a veritable junkyard of broken genes, ancient viral DNA (see also Discovering Retroviruses: Beacons in the Biosphere), and stretches of self-copying DNA (or transposable elements). Together, these make up an estimated 97% of our genome and were initially designated “junk DNA”, though there has been a bit of a push-back against the idea that this material is completely useless (see e.g. Junk DNA: A Journey Through the Dark Matter of the Genome or The Deeper Genome: Why There is More to the Human Genome Than Meets the Eye).

And then there is our reproduction, marred by poor fertility and high mortality during childbirth. Autoimmune diseases, allergies, optical illusions, false memories, cognitive biases… True to the promise of the book’s subtitle, Lents offers a panorama of our glitches, and there is something here for everyone to enjoy.

I found the chapter on our brain and its quick-and-dirty heuristics (i.e. problem-solving routines) particularly fascinating. Our cognitive biases and weaknesses regularly drive us to make poor choices, and this knowledge is ruthlessly exploited by advertisers, casinos, or astrologers, to name a few. I also find them particularly interesting as they lead to much irrational behaviour and persistent belief in pseudoscience (for more on that, see amongst others Thinking, Fast and Slow or Suspicious Minds: Why We Believe Conspiracy Theories).

“Our cognitive biases and weaknesses [are] ruthlessly exploited by advertisers, casinos, and astrologers.”

Do not let its focus on our many flaws fool you. Human Errors is an excellent piece of popular science, that, far from being a downer, is more a laugh-out-loud romp that will give you reason to marvel at our ability to be successful despite all our imperfections. Some of these are truly pointless, others result from trade-offs, others still have been turned from bugs into features, and not infrequently things that used to serve us well in our evolutionary past no longer do so now (see e.g. The Hungry Brain: Outsmarting the Instincts That Make Us Overeat, Mismatch: The Lifestyle Diseases Timebomb, or Mismatch: How Our Stone Age Brain Deceives Us Every Day And What We Can Do About It). But with all of them, Lents explains plainly and clearly how evolution works and is shaped by what has come before.

As a final aside, you will notice that I have carefully steered clear of using the word “design” in this review, tainted as it has become by creationist appropriation. But if I must: yes, humans seem poorly designed on many fronts compared to other organisms. If you were an engineer tasked with designing a human, you would make many changes. In this context, Adam Rutherford said that this book shows that: “if there is an intelligent designer, he is comically hopeless”. Quite.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Human Errors paperback, hardback, ebook, audiobook or audio CD

Other recommended books mentioned in this review:

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“Should We Control World Population?“, written by Diana Coole, published by Polity Press in July 2018 (paperback, 138 pages)

Divided into three parts, Diana Coole first asks whether there actually is a problem, as plenty of people will disavow overpopulation as being a problem to begin with. Covering developmental, environmental, existential, and economical arguments, she concludes that there are good reasons to try and control human population numbers. An example of a developmental argument is that overpopulation is not in the interest of poor countries. An example of an existential argument is whether a world completely dedicated to supporting a huge human population is in the interest of our well-being. Economical arguments on the other hand often end up pro-growth, given the costs of a large, ageing population.

Out of these four, especially the environmental argument is one that is rapidly becoming impossible to ignore, and I happen to think that overpopulation is the mother-of-all-problems where environmental degradation is concerned. As I argued in my review of The Irresponsible Pursuit of Paradise and is also recognized in this book, a large human population multiplies the impact of our lifestyle. No matter what lifestyle this might be, you always have an impact. I get the impression this is often lost on advocates of sustainable development and green alternatives such as renewable energy. Coole touches on the framework of planetary boundaries developed by Johan Rockström and colleagues. In my opinion, it is important to realise environmental concerns go well beyond the extinction of some cute, furry animals. This is affecting the very fabric of our planetary ecosystem that we as humans also depend on. Ecologists describe this under the umbrella term of ecosystem services (there is a large literature on this, the Routledge Handbook of Ecosystem Services is but one of many starting points).

The other two chapters deal with the ethics and the means by which we could actually control population numbers. Coole argues that there are some clear ethical boundaries that cannot be crossed, especially where women’s rights and bodily integrity and autonomy are concerned. It stands to reason that we think forcing an abortion on a woman violates basic human rights. But the other side of the coin, that forcing a woman to continue an unwanted pregnancy by making abortion illegal, is equally problematic, but far less widely accepted. She discusses access to reproductive health services such as family planning and birth control, and whether it is ethical to yield these as tools to steer decision making by couples. Finally, there is the question of the ethics of family size. I found the argument put forth by Sarah Conly’s book One Child: Do We Have a Right to More? very relevant.

“[…] environmental concerns go well beyond the extinction of some cute, furry animals”

Last but not least, how do we actually go about influencing population numbers? Coole makes a strong argument that in democratic societies we already have a system of mild coercion through laws, taxes etc. to influence people’s behaviour. And often such tools have already been used to influence people’s reproductive decision making through tax reliefs, childcare support, housing schemes etc. used either to encourage or discourage population growth and family size. If we see no problem in governments manipulating consumer behaviour to mitigate environmental degradation, cold logic says we should apply this to human population numbers as well. A tiny problem that Coole also highlights is that many countries where the problem most urgently needs addressing are not democratic countries, but authoritarian regimes or failed states.

It is only all too easy to fall into extremes when trying to discuss this topic. My own views could safely be called controversial. It is widely documented that increased economic development and education of women reduces family size and is, in the long-term, predicted to lead to global population stabilisation if we could realise this globally. However, I am seriously concerned that it will be too little, much too late, which logically would force our hand to more drastic measures. On a bit of a tangent, I never cease to be amazed that couples wishing to adopt have to go through many hoops to show that they will be reliable parents, but that literally any nitwit can have children the old-fashioned biological way. Isn’t it time we introduced compulsory certification for prospective parents, thereby capping population growth? (I will immediately admit that this is far from a well-developed argument, and I can see it being problematic to implement – who judges the judges?)

Obviously, my ideas will be way too extreme for most, and this book has forced me to think about more widely applicable and realistic measures. Though the reading might sometimes be a bit heavy on theoretical ethics, Coole immediately convinces that we can no longer ignore the elephant in the room. This slim volume does not provide all the answers, but it is an opening salvo for a much-needed, broader discussion.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Should We Control World Population? paperback, hardback or ebook

Other recommended books mentioned in this review:

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