How many of the Four Horsemen of the Apocalypse can you name? 

Most people manage a couple, maybe three, medical historian, Dr Emily Mayhew, tells me. But “pretty much everyone in the world has heard of them, regardless of their faith tradition.”

The imagery of the Four Horsemen has persisted for over a thousand years because these four biblical figures represent ever-green threats: War, Pestilence, Famine and Death. 

The horsemen have provided Mayhew with the structure to her four-part book. It’s a book about the threats facing humanity, but also “the hope of a new age” – the extraordinary humanitarian projects and scientific developments that help keep the Four Horsemen at bay. 

It’s her entree into the world of ‘popular science,’ and for a historian whose previous work has focussed on severe casualty in warfare, it’s an ambitiously broad theme.

In some ways, it’s difficult to give a real flavour of what the book is about because, in just over 300 pages, Mayhew covers an enormous amount of ground. 

It begins in war-torn Mosul and ends in tsunami-ravaged Indonesia – and, along the way, we meet an eclectic group of individuals – from Peruvian farmers sequencing potato genomes to stave off crop disease and famine, to scientists in the UK, manufacturing an artificial surface, resembling shark’s skin, to fend off bacteria. 

Despite its varied explorations, the book never feels jumbled. Mayhew skilfully portrays the interconnectedness of all the subject matter and, in many ways, this is the central message of the book: human threats overlap in more ways that we often realise. “The Four Horsemen always ride together.”

Recognising the interconnectivity of our issues and collaborating across disciplines is our best bet for managing threats. Or, as Mayhew puts it, “building a line against one Horseman usually ends up holding the rest of them back too.” 

Malnutrition specialists and infectious disease specialists, for instance, should work together. Her description of malnutrition as an “immunodeficiency syndrome” is a stark reminder of the ways famine and pestilence intersect. (And, as we know, famine is so often a byproduct of war.) 

“Truly interdisciplinary work is rare but it’s so effective. We need to join up the dots, come out of our silos and see beyond our field,” Mayhew argues.

Her book is unquestionably timely. And readers may be surprised to learn that it was largely written pre-pandemic. In the early days of writing, she tells me, some had even suggested she replaced the ‘pestilence’ section with a more ‘relevant’ one on pollution. 

She recalls sending a first draft to her publisher as a mysterious virus was first emerging in Wuhan, with a note at the bottom saying, “I think this coronavirus might be worth some attention, so we better see where that goes.”

The book’s exploration of “the strength of the microbiological world to confound us” resonates strongly. But, while the book is now laced with references to coronavirus, even more arresting is Mayhew’s section on antimicrobial resistance: as bacteria strains become increasingly resistant to antibiotic treatment, our ability to conquer bacterial infection is fading. Present fears surrounding vaccine-resistant mutations make this looming threat feel especially salient. And Mayhew hopes that the coronavirus will be spur on more research and development on antimicrobial resistance. 

Despite the heavy subject matter, The Four Horsemen is a hopeful book. It homes in on the extraordinary work of individuals to keep human suffering at bay. And it shines a light on the potential of science to overcome threats. AI is presented as an agent of great hope; it has already been used, for instance, to identify the previously undiscovered antibacterial powers of the drug Halicin. “I have absolutely no doubt that we’re going to find most of our repurposed drugs through the use of AI,” Mayhew says. 

And while it may appear a less novel solution, she hopes the book will help readers to understand the value of vaccination “to a very profound level”. Vaccinations are “healthcare systems by other means,” she argues. They offer a model of healthcare which places the emphasis on prevention rather than cure. More vaccines means fewer infections, fewer infections means less use of antibiotics, less use of antibiotics means less chance of antimicrobial resistance developing.

Another hopeful message from the book is that human disasters can be catalysts for good. The devastating 2004 tsunami brought peace in Aceh, Indonesia; warring factions recognised the imperative of working together to rebuild their decimated country. 

Might the coronavirus be a catalyst for some good? Mayhew hopes it will bring a greater understanding that, when scientists and governments collaborate across borders, we can “force the riders to a draw”. 

She is careful in her choice of the word “draw”. “I’m really trying to avoid the ‘battle’, ‘defeat’ language,” she tells me. To do so would undermine one of the book’s central messages. 

There is a reason why the Four Horsemen have lasted for so long as a metaphor: because what they represent is still with us and likely always will be. In general, we manage threats as opposed to eradicating them. 

But, Mayhew hastens to add, “if governments, research institutes, universities, hospitals and commercial entities continue to communicate with each other and work effectively, then there is no draw we cannot hold.”