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Scanning the Trees

Do you ever find yourself worrying about the worst things that could happen? If so, it's not your fault and you are not alone. Our brains feature a Default Mode Network that is activated whenever we don't have much else to focus on. This web of tightly connected neurones, across the medial prefrontal cortex, posterior cingulate cortex and angular gyrus, is responsible for many of the unbidden thoughts that come to us in such times. It is there to help us make use of our brains when they would otherwise be underoccupied, by guiding us to reflect on our goals, review our relationships, and scan our environment for possible threats, like tigers lurking in the trees. In our ancestral environment, humans used this part of our brains less often, because we had so much to keep us occupied, and, when we did, it helped us take action to stay safe, develop ourselves, and strengthen our relationships. However, in our present environment we are often understimulated, meaning it engages more often, but we also lack clear opportunities to improve our situation. This is why our minds gravitate chronically towards personal inadequacies and everything that could possibly go wrong.*

Right now, there is a lot that could go wrong. In one hundred years' time there might be no humans still alive. Or it could be that while some of us survive we do so in conditions of squalor, conflict, and isolation, which many reading this book would struggle to imagine. Neither of these outcomes is guaranteed, far from it, but they are certainly possible.

I work in the emerging field of Existential Risk Studies; I spend my days thinking about these possibilities and how to avoid them. It would be nice to say, 'I spend my days thinking about this, so you don't have to.' However, I don't think that would be very helpful. For one thing, my thoughts may not be the right ones. For another, I certainly wouldn't want to say that I could do this by myself. And, for a third; well, I suspect a lot of you may be thinking about these possibilities anyway. So, I would rather say 'I spend my days thinking about these possibilities so that, when you do so, your thoughts might go beyond worry and doubt and be constructive and hopeful.' That is why I am writing this book.

A question that I am often asked is 'what should I be most afraid of?' And my answer is always the same. I don't want you to be afraid of anything, so in the pages that follow I will do my best to talk honestly and candidly about humanity's existential predicament with as little alarmism and as few triggers as I can. I don't want you to be afraid, because fear is not a very motivating emotion. Fear, for me, is something that makes me pull the duvet over my head. For our ancestors, fear was something that made them scan the trees, stay still, or find shelter, even if that meant putting off food gathering, camp building, or other essential activities. However, I don't think you should do that. I think that, by now, most of us have a pretty good idea where the danger lies, and we increasingly understand what to do about it. We gained this knowledge from hundreds of years of work by scientists and visionaries, authors and activists standing on each other's shoulders. What we lack are 8,200,000,000 humans who all feel empowered to go out and use it!

Still, it's helpful to briefly scan the trees and remind ourselves where those tigers are before proceeding.

Deadly diseases

A fear that has dogged humanity since the dawn of civilization is disease.16 We live in a complex and flourishing microbiome: every breath of air you take, every sip of water you drink, and every patch of earth you stand upon is literally teeming with microscopic life. All but a tiny, tiny fraction of these organisms are no threat to us whatsoever. For instance, there are more cells in your body that belong to microorganisms than there are human cells; most of them are helpful and without them you would be very unwell. Some microorganisms are helpful if they are in some parts of our bodies (such as our gut) but can be harmful in others. Only a few have evolved to have purely pathological relationships with us, making us sick. However, even these pathogens will normally harm us only to the extent that this is helpful to them (such as by hijacking our cells to replicate themselves). If they harm us too much, then that is likely to harm them as well (the death of a host often means death for their pathogens too). It is a fundamental law that whatever reproduces the most will spread, and this is generally not the most harmful form a pathogen could take. Evolution works by harnessing this simple fact to power processes of variation, in which possibilities are created, and selection, in which those that spread will tend to replace those that do not.*

However, as we know, a few pathogens can and do make us very sick and even kill us in large numbers. Sometimes this is because facts about us (such as age, malnutrition, or multiple infections) make us especially vulnerable to them. Poverty, population ageing, urbanization, and global travel all serve to increase these vulnerabilities.17 However, pathogens can also be deadly because evolution sometimes works in unusual ways. For instance, it is generally the case that when people get slightly sick, they carry on moving about, infecting others as they go, but when they get very sick, they stay put and don't see others.* This tends to give an evolutionary advantage to milder pathogens, leading them to outcompete their more deadly peers. However, in certain extreme conditions, like disasters and wars, the opposite can happen. People who are slightly ill may stay put and only the sickest are evacuated for treatment elsewhere. This helps deadlier strains of diseases to spread, giving them the evolutionary advantage. It is thought to be one reason why the 1918 influenza pandemic at the end of the First World War was the deadliest of the century - killing more than twenty million people, many of whom were young and fit.18

The other way that pathogens become very harmful is when they are (relatively) new and evolution hasn't had time to work yet. Deadly pathogens often emerge when a disease is transmitted from one animal (in which it may only cause a mild illness) to another (in which it may be, accidentally, far more lethal). This is called zoonosis, and it is the origin story for many of our most feared plagues - from smallpox (originating from gerbils about 4,000 years ago) to HIV (from chimpanzees in the early twentieth century) to Ebola (from fruit bats in the 1970s). Other pathogens, like influenza, experience relatively frequent retransmission between species, occasionally causing new flare-ups of significantly more dangerous disease. To be clear, most zoonotic diseases are neither deadly nor transmissible between humans.* However, due to their unpredictability, zoonotic diseases can be far more dangerous than those endemic to our species.

Yet, these are unlikely to remain the most dangerous of diseases humanity will ever face. This is because, even though zoonosis can circumvent evolutionary pressures that tend to make diseases less dangerous, at least they are not designed to be as dangerous as possible. At some point, we are going to have to contend with pathogens that have been so designed, by scientists working in laboratories. In fact, such pathogens are already being developed both for important medical research, to investigate how new pathogens might emerge and what we can do about them,19 and (probably) to develop bioweapons.20 This work is carried out under strict safety protocols. However, as these kinds of dangerous research become cheaper and easier, the number and diversity of people working on them is growing, increasing the risk that pathogens will either be released accidentally, because of unforeseen escape routes or simple human error, or intentionally used to cause harm.21 Estimating this risk is very challenging. Rival studies in 2014 and 2015 put the expected number of deaths from one laboratory working on this kind of research for one year between 0.0000222 and 1,400,000.23 This has not been made any easier by the significant controversy surrounding the idea that COVID-19 may have originated from such experiments - my own view is that it almost certainly did not.

However, we will not have to face those threats empty-handed. While much of human history has seen a rising tide of deadly diseases, caused by urbanization, agricultural intensification, global trade, colonialism, and war, the last 250 years have seen us turn that tide, at least to some extent. The greatest advances came from the discovery of vaccines in the eighteenth century (using weakened or altered forms of pathogens to train our immune systems to fight them more effectively),* improvements in sanitation during the nineteenth century (especially clean drinking water, widespread hand washing, pasteurization, and refrigeration), and the development of antibiotics in the twentieth century (harnessing the natural tools moulds develop to fight bacteria). Meanwhile, the same biotechnologies that create the possibility of engineered pathogens are also paving the way for further developments that may be even more significant than these in the fight against disease. We are also starting to better understand social responses to disease (both positive and negative) and how these can be used to buy crucial time in the...