Air-Borne The Hidden History of the Life We Breathe

Many of you will likely never have heard of aerobiology. To explain why the science of airborne life has remained one of biology's more obscure disciplines, well-known journalist and science writer Carl Zimmer once again delves into archives and interviews scores of people to unearth a most remarkable history. Air-Borne reads like a real-world thriller, filled with human ingenuity, persistence, hubris, and arrogance; with pandemics and biological weapons; and, so it seems, with every bad decision under the sun.

Air-Borne is not a small book. Zimmer has consulted twenty archives in thirteen different institutes, interviewed scores of people, and covers some two centuries of scientific and medical developments in 469 pages, 20 chapters, and five parts. By the time you finish the book, though, you will understand why: doing justice to the complex and multifaceted history of aerobiology requires that he covers a lot of ground. To give you a taste of this, what follows is a brief rundown of what I think are the five main beats of this history.

First and very important is the long struggle between miasma theory, the idea that bad air caused sickness, and germ theory. This part is a fascinating history of the emergence of a public health movement, of surprisingly stubborn attempts to find a single cause for all diseases, and of experts seemingly getting things right for the wrong reasons. Both camps pursued sensible public health measures, which, of course, did not help defuse the debate. Though miasma theory was eventually abandoned, it cast a long shadow: very few people were now willing to entertain the idea that some diseases are, in fact, airborne.

The second beat is easily the most fun one and charts the history of scientists sampling the outdoor air and discovering it was full of bacteria, spores, and viruses. A series of pioneers used kites, balloons, and early aeroplanes to figure out just how high up life could be found, and how far it could travel. This is where we encounter Fred Meier, arguably the father of aerobiology, who developed a grand vision to sample our atmosphere more systematically. Had he not died aged only 45, he might well have succeeded in unifying the indoor and outdoor factions. Without him, however, the movement lost steam and both factions continued to work in their own silos, barely taking note of each other's findings.

Here, Zimmer pivots to the third beat: the lives and careers of husband-and-wife team William Firth Wells and Mildred Weeks Wells. They became interested in airborne droplets as agents of disease transmission, especially small droplet nuclei or aerosols. Their experiments in the 1930s and 1940s on tuberculosis gave tantalising evidence for airborne transmission. However, it was never enough to convince their many critics who, at best, would allow for diseases to spread in large droplets that quickly fell to the ground once emitted by a sneeze or a cough. What did not help was their reputation as difficult people to work with. William, in particular, was often his own worst enemy, almost incapable of expressing his ideas clearly, constantly tweaking and rewriting his attempt at a book, while arrogantly convinced that, surely, the next set of experiments would rewrite the history books! This part might test your patience as Zimmer skillfully channels the exasperating character of William, but bear with it, it will be relevant later.

While fellow scientists showed little interest in the work of the Wellses, one group of people did: the US military. The fourth beat is easily the most harrowing. The army had no problem in accepting that diseases could be airborne, weaponised aerobiology as World War II got underway, and produced a vast arsenal of biological weapons. This spiralled into an arms race with the Soviety Union as the country entered the Cold War, scarring the country's national psyche to this day. It also offers one explanation for why aerobiology remains so little known: more so than other disciplines such as physics, the young field of aerobiology "was entirely engulfed by the military" (p. 209). They trained thousands of people, yes, but these were all sworn to secrecy and worked towards a narrow set of goals.

Despite a short palate cleanser of more recent studies on the aerobiome, the looming spectre of the fifth beat hangs in the air: our recent brushes with SARS, Ebola, and MERS before things went properly off the rails with COVID-19. There ensued a two-year struggle in which public health bodies denied that COVID-19 was airborne, while a small group of scientists clamoured for this possibility to be taken seriously. It is another nail-bitingly tense part of the book, full of human hubris. It is also where the earlier storyline of the Wellses becomes relevant again. Public health experts continued to believe COVID-19 was spread in large droplets that quickly fell to the ground with only droplets smaller than five microns staying airborne. Wells is credited with establishing this rule, except that he never did. Zimmer here chronicles the sleuthing that identified how his findings were misinterpreted and taught to generations of epidemiologists in a "misreading [that] would grow into a major misunderstanding in later years" (p. 244).

The above is only a broad-brushstrokes overview. As mentioned, it is a complex history, but one that is in good hands with Zimmer, the different beats building narrative tension. He remains impartial and non-judgmental even when dealing with the horrific history of biological weapons, refraining from constantly interjecting his personal opinion. The focus on weapons and pandemics almost overshadows the equally interesting research on the outdoor aerobiome, which is not a knock against Zimmer but an accurate reflection of how the discipline has developed. Finally, in the wake of COVID-19, a new generation of scientists would rediscover Wells's work and lionise him as a visionary. A small, but in my opinion particularly sweet detail is how Zimmer's biographical work allows him to gently push back on this rosy portrayal. It overlooks Wells's struggles and difficult character, and ignores (once more) the contributions of Mildred "who had done so much on airborne infection both with and without her husband" (p. 385). There is never not an appropriate moment to celebrate forgotten women in science.

Many people were inspired to write books in the wake of COVID-19. Zimmer's question as to why its airborne nature was denied for so long has resulted in the most remarkable and unexpected pandemic-related book I have read thus far. Whether or not you are already familiar with Zimmer's writing, Air-Borne comes highly recommended.