The planet we live on is positively crawling with life. There is not a nook or a cranny, it sometimes seems, where we don’t find some odd species of worm, some crawling slime or microscopic organism. Again and again, we drill or submerse or dig and we find new kinds of life, farther down than we thought possible, colder than we thought possible, hotter, more acidic, weirder.
Every one of those plants and animals and prokaryotes and whatnot—every single one of them—came into existence from another of their kind. Some reproduce sexually, some by budding, some by division, but all from a parent organism more or less identical to them. As we run backwards in geological time, however, this great chain of living things must have had some first beginning, some origin, that did not involve a parent of the same—or indeed of any—species. Living things, now, may all come from parents of one sort or another, but life itself had, once upon a time, an absolute beginning. Matter that was utterly nonliving somehow turned into matter that was now living. Perhaps just once or at any rate not often, but one time at a minimum, somewhere and somewhen in the cosmos, a living thing must have just come into existence. Pop.
But this is a very new way of thinking. From antiquity to the Middle Ages, from Aristotle on past Vesalius, Galileo, Newton, and after even Darwin, it appeared that this kind of thing, life from non-life, happened all the time. Maggots, famously, but also eels, bees, mice and sometimes even people—think about that—just sprang into existence from putrefying, dead matter. True, the list of organisms took some hits over time, eventually whittling down to just microorganisms or a few parasites like liver flukes, but the idea that life could come from non-life, regularly and routinely, was a remarkably hard one for us to shake.
Why is that?
This book argues that one of the main reasons is that the evidence for spontaneous generation is, when you look hard at it, really quite good. There is a reason spontaneous generation was a fact for so long: it stands up to testing—and very, very good testing—remarkably well.
By diving in to the debates around spontaneous generation as they unfolded historically, this book raises some important philosophical questions about what it means to do science, to understand nature. From its earliest articulation in Aristotle, all the way to the end of its plausibility as a fact about the world, we find that the problems posed by spontaneous generation provoked some very good, very hard thinking about what life was and how it could possibly come to be from nonliving matter. This is no easy problem, in fact. This story is emphatically not one of primitive thinkers failing to see the simple evidence, the easy tests (just cover the vials! Just boil the solutions!), right before their eyes. Not at all. Instead what we find is a long series of remarkably intelligent approaches to the evidence for spontaneous generation, struggling to figure out which animals might come to be in this way, and even more importantly: How?
Spontaneous generation is one of those wrong theories that clutter the basements of the biological sciences and that now look so very obviously wrong that it is hard to see how anyone could have taken them seriously in the first place. Why wouldn’t it occur to anyone that flies might be laying eggs that were too small for us to see? How simple would the crucial experiment be? What I have tried to do in much of my work is to turn this ‘obvious wrongness’ on its head—why, exactly, does it seem so obviously wrong?—and see what the new picture that emerges from that inquiry says about science and our belief in its results. By taking spontaneous generation seriously as a sophisticated and above all a well-supported idea, I try to breathe new life into a world where processes that we, today, can’t even really imagine as plausible, were instead vivid, clear, and their details were hotly (and fascinatingly) debated. The epistemological disjunction—for my own part it is sometimes akin to vertigo—that this inquiry produces can shed some startling new light on how and why we think the way we do about the sciences, their authority, and even the realness of the entities and laws that they affirm or deny.
There was a moment in the thirteenth century, when the great polymath Albertus Magnus held in his hand an exquisitely wrought ancient onyx cameo. He went on to describe it in beautiful and elaborate detail in his book On Minerals. His description is careful and exact enough that modern historians have been able to identify the specific cameo as one now in the Kunsthistorisches Museum in Vienna.
Take a moment now to appreciate its details—it really is a gorgeous piece of work. Because of its relative hardness (a seven on the Mohs scale), its near-translucency, and its dramatic variations in colour, onyx makes for some of the most beautiful relief work that comes to us from Greco-Roman antiquity, and examples of such work can be breathtaking, as many a museum-goer can attest.
So what is this object that we, now in communion with Albertus, have before us? A ten-centimetre-or-so pendant, bearing the silhouettes of two people in elaborately decorated military headgear. A snake adorns one helmet, as do a winged thunderbolt, a bearded man with horns, and a number of other decorative elements.
But here is the rub: without even thinking about it, you and I immediately recognize the skill of the person who carved the cameo, who carefully removed layer after layer to take masterful advantage of the stone’s difficult-to-predict layers of colour. But—almost shockingly to my mind—Albertus did not see this skill at all. Not one whit of it. Instead Albertus thought the stone was produced by natural processes, in the earth, just like any other stones. This gorgeous, detailed cameo just happened. That, it seems to me, bears explaining.
Creatures Born of Mud and Slime is an attempt to make sense not just of how Albertus could think the way he did about this one object, but also to delve into the details of the mechanics, of the physical and biological forces, that were at play for him in its production. For Albertus this involved the stars and planets bearing down, in astrological influence, on the forces that shaped the production of stones here on earth. These forces were identical to, he tells us, the forces that produced the many kinds of animals that, like the cameo, were generated spontaneously. Like many before and after him, he theorized the process of spontaneous generation in remarkably subtle and well-informed ways. This raises important questions about what premodern approaches to things like this cameo can tell us about our own approaches to the natural world and how we understand observation, evidence, and theory today.
Spontaneous generation as a mechanism for producing animals is generally seen today as a kind of simple, historical, ‘common-sense’ idea that grew out of people’s naïve inability to see, or even imagine, tiny things like fly-eggs landing on rotting meat. And so the idea that maggots just ‘come to be,’ directly, from rotting refuse is seen as a natural response by premodern thinkers arising from their impoverished imaginations. Creatures hits that idea with a hammer: a close examination of the sources who discuss spontaneous generation shows that people continuously questioned the idea of spontaneous generation in complex and sophisticated ways. Not only did they think hard about how such a mechanism could work for the generation of life from nonliving matter (it is very much a non-trivial problem), but they also continuously examined whether particular animals really were spontaneously generated or whether they could be shown to generate sexually instead.
And the evidence for spontaneous generation was, as I have said, really good, even (and especially) when it was examined very hard. The fact that spontaneous generation is the product of some really good investigating, while at the same time being no longer true, raises some important and difficult questions about science and its epistemology today.
And when I say that spontaneous generation is no longer true, that is not quite right. Something like it did, after all, happen at least once. This positively infested earth that we live on is sufficient testimony to that fact.
Some years ago now, I came across a casual reference in Ptolemy to a fact that he just took for granted about the world: that if you get garlic on a magnet it will wreck the magnet. Tracing the history of this claim—and it gets reiterated no small number of times—to its eventual dissolution proved a fascinating exploration of how obviousness infects our thinking about the world (see my What Did the Romans Know? for the details). When I started on the project the would become Creatures Born of Mud and Slime, I thought that spontaneous generation might work in much the same way as garlic-magnets. I was wrong.
Instead, spontaneous generation is a much richer, much more complex, and much more wonder-filled ground in which to explore fundamental questions about how people think about evidence, plausibility, matter and material forces, and processes that somehow transcend the materiality of those forces. True, as with garlic and magnets, what we think of as obvious is challenged again and again as we engage with very different ways of looking at the world and different ways of making sense of our experiences in it. That, to my mind, is both humbling and fascinating. I suppose it’s why I’m in this business.
Daryn Lehoux is Professor of Classics and Philosophy at Queen’s University. He is the author of Creatures Born of Mud and Slime (featured in his Rorotoko interview), What Did the Romans Know? (University of Chicago Press, 2012), and Astronomy, Weather, and Calendars in the Ancient World (Cambridge University Press, 2007). He is also the co-editor, with A. D. Morrison and Alison Sharrock, of Lucretius: Poetry, Philosophy, Science (Oxford University Press, 2013).