Life as Slime
Prominent scientists continue to claim life is “just” slime on a spinning rock. However, in an age when the rarity and fragility of life are increasingly evident, it’s time to retire the metaphor.
This article concludes Issue 06. Watch our Behind-the-Scenes interview with the author on YouTube.
By Thomas Moynihan
In 1832, Ferdinand von Ritgen, a German physician, puzzled over how the first generation of humans birthed themselves. He pictured their embryos sprouting spontaneously “without procreating parents preceding them,” like fungal growths emerging from the ground.
By Ritgen’s day, it was understood that life on Earth had predated humanity’s debut for eons and that living creatures had increased in complexity across that duration — but it wasn’t understood how novel forms appeared. A twenty-two-year-old Charles Darwin had boarded the HMS Beagle only a year before, his theory of evolution as yet unconceived. Given available knowledge, Ritgen’s conjecture made sense.
A seasoned obstetrician, Ritgen knew firsthand the intricacies and difficulties of childbirth. As there would have been neither mothers nor uteruses to incubate these first fetuses, he reasoned that nature must have provided substitutes. He imagined seedpods sprouting around the fetuses, cupping them like protective wombs. Ritgen claimed these would have resembled the fleshy blossoms of Rafflesia arnoldii, better known as the “stinking corpse lily” because of how it emulates the smell of corporeal decay to attract pollinators.
Ritgen pictured the “first child awakening in the calyx” of this “gigantic flower,” swimming in the amniotic bliss of its “milky sap.” These “leathery” chalices, he remarked, would have germinated in “Uferschlamm,” the riverside mud. He pointed to countless other organisms that seemed to emerge, without prior parents, from slime: mites, algae, jellyfish, lice, and even intestinal worms. At the time, the idea of gestation without prior procreation had not yet been satisfactorily disproven.
Of course, some weren’t impressed. Theologians decried that by implying we weren’t descended from Adam, Ritgen demoted us to “fungus-people” with a pedigree that was but a nativity of slime. They deemed his idea yet another noxious fruit of scientific “nihilism,” budding alongside all the other godless theories shooting up “like disgusting mushrooms in the pathologically productive soil of our time.”
Ignoring Ritgen’s excusable ignorance of the Darwinian steps that separated slime from simian, his basic sentiment lives on today. Even the eminent Stephen Hawking, appearing on a 1995 BBC documentary about cosmology, voiced the motif before the credits rolled: “The human race is just a chemical scum on a moderate-sized planet, orbiting around a very average star in the outer suburb of one among a hundred billion galaxies.” Hawking delivered this assertion with the vestige of a grin.
For many centuries, misanthropes and humanists alike have indulged in similar comparisons. But this argument has metamorphosed alongside scientific understanding. Where we used to think life was overabundant, we now recognize that it may be staggeringly rare.
Biotechnologists know this firsthand. Several decades of effort to create “artificial life” in the laboratory have produced biochemical machines and self-sustained protein production systems but, as yet, no organisms capable of cell division or robust metabolism. Astronomers, similarly, have scoured outer space for signs of life since 1960, and still haven’t found convincing evidence of biology beyond Earth’s atmosphere — though the search continues.
So, is it right to say biology is “just” a planetary fungal infection? The answer, as it turns out, depends on whether the “just” disparages something lowly or underscores something breathtakingly unique.
Life’s Effortless Origins
Our understanding of life’s cosmic place and prevalence has evolved since Ritgen’s time. As his conjecture reveals, the defining boundary between organic and inorganic was once quite blurry. Visions of animals naturally springing from wet mud go back to the pre-Stoic philosopher Anaximander, but Ritgen had been more immediately preceded by Lorenz Oken, another German naturalist who argued all life comes from “Urschleim,” the primordial slime.
Having studied sea snails on a remote Frisian island in 1806, Oken became convinced of the cosmic centrality of mucus. He theorized an existence replete with microscopic gelatinous globules that spontaneously clumped together, cooperating like a hive to form complex organisms.
“Everything organic has emerged from mucus,” he announced, “and is nothing but mucus in various forms.” Oken saw this coating of self-agitating slime as a natural, unavoidable outcome of “planetary evolution.”
Back then, the very category of the “inorganic” — describing that partition of matter that precedes all living processes and requires no relation to biology — had yet to be clarified. Before roughly 1800, “inorganical” was instead used to denote the “spiritual” realm. There wasn’t yet awareness that organic compounds, though prevalent on Earth’s surface, represent a special manifestation of matter, whose omnipresence on our planet is conditional upon a set of highly specific conditions stretching back billions of years.
Charles Darwin’s own grandfather — Erasmus Darwin, a celebrated naturalist and abolitionist — provides an exemplary case. During the years straddling 1800, he theorized that organic sludge creates rocky planets, rather than the other way around. Understanding that limestone and chalk are formed from compressed shellfish and other organic remnants, Darwin extrapolated this to the scale of the entire globe.
In 1791, alluding to the ways coral polyps form new islands, he proposed that our planet began as one unfathomably deep ocean, teeming with algae, foraminifera, and other microorganisms. These then “generated” the solid body of the world, through long eons, via “vegetative” processes; namely, by passing the seawater “through their organs of digestion,” converting it to chitin, shell, and carapace. This is likely why Darwin added the Latin motto E Conchis omnia, “everything from shells,” to the family coat of arms.
This meant, for Erasmus, even mountain ranges must once have flowed from the organic peristalsis of living creatures, constituting later “monuments” of anciently satisfied hungers. Accordingly, England’s limestone peaks appeared to him to “constitute monuments of the past happiness of those organized beings.”
Unlike Erasmus Darwin, we now know organic compounds comprise only a tiny percentage of the Earth’s entire crust. Carbon — the major component of all terrestrial life — only accounts for around 0.03 percent of the Earth’s entire mass. What’s more, recent studies estimate Earth’s total living biomass weighs around 550 billion tons in total. For comparison, Mount Everest alone is about 161 billion tons. This puts into perspective how tiny a fraction of matter is, or was ever, alive. And that’s just here on Earth. Taking a wider perspective, only 5 percent of the universe is composed of atoms. Of that 5 percent, all atoms that are more complicated than hydrogen or helium — those that might develop into life — comprise only 0.1 percent.
In Erasmus Darwin’s day, however, none of this was known. Other early theorists made the boundaries between living and unliving even more porous, conjecturing not just that ocean depths can generate complex creatures from scratch but the thin air as well.
Such was the opinion of J.G.J. Ballenstedt, a Prussian paleontologist who, in 1824, announced his belief that Earth’s atmosphere effortlessly “secretes” swarms of organisms. This, in Ballenstedt’s eyes, was the only sensible explanation for reported showers of “worms, caterpillars, butterflies, even toads, frogs, fish, snakes, and other animals.” The “immense hordes” of locusts which block the sun for hours on end “seem to me,” Ballenstedt averred, “to be a product of the air and not to originate on Earth.”
Indeed, from a purely empirical standpoint, it does appear that life crops up everywhere it can. Food readily goes rotten, wounds easily become infected, damp quickly turns to mildew.
Our planet’s surface appears overripe in this way, but it took generations of inquiry to gather the evidence sufficient to determine that this pullulation of organic matter is perhaps found nowhere else in the universe. It holds true on Earth — and, for all we know, only on Earth — because an unimaginably stringent series of preconditions unfolded here.
Not only is our planet in an auspicious location in an auspicious type of galaxy, but it orbits at the right distance around the right type of star. It also remains geologically active — and it’s widely considered that plate tectonics aids biology by sequestering carbon and pushing minerals useful to life closer to the surface. Additionally, chaotic collisions between it and nearby objects in the early solar system may have contributed to the chemical soup necessary for life. What’s more, life plausibly appeared at just the right time to enter into stable chemical feedback with its planetary environment, so as to become ubiquitous and persist for the four billion years of accumulative evolution required to create us.
But back in 1824, none of this was known. The Origin of Species hadn’t yet been published, let alone its wider ramifications digested. In Ballenstedt’s day, therefore, shortcuts to complexity couldn’t be comprehensively ruled out.
One seemingly undeniable case of spontaneous generation, for Ballenstedt and others, was that of “intestinal worms.” It had been verified that adult tapeworms perish immediately outside of the intestines, but not that they reproduce via microscopic eggs that survive and spread beyond the original host. Accordingly, Ballenstedt puzzled over the “first tapeworm.” “Do we perhaps,” he asked, “assume the first human was created with every species of intestinal worm … ?”
Struck by this, he concluded Adam, being the first human, “would have been a true cross-bearer,” a kind of Noah’s Ark of infection. God wouldn’t allow any of his creatures, even the lowliest, to go homeless. Aghast, Ballenstedt queried, “Was he not in danger of being eaten alive by vermin?”
But such conjectures — of life popping up wherever and whenever it can — were slowly replacing belief in supernatural creation and a Biblical Adam. Ironically, “protoplasm” eventually took prominence over Oken’s “Urschleim.” Coined by Czech anatomist J.E. Purkyně in 1839, “protoplasm” was a riff on “protoplast”: an old liturgical title reserved for Adam, deriving from the Ancient Greek for “first-formed.”
Life as Cosmic Rarity
This leads to a crucial point. In such a context, where it was widely assumed biology effortlessly crops up everywhere — in our stomachs, in the stratosphere, in ocean depths — it became possible to denigrate life by comparing it to a common pestilence. Putrescence, after all, is but another description for an overabundance of life.
None other than Ballenstedt himself appears to have come early to this notion. In an 1819 essay, exploring the relation of Earth to the wider universe, he compared the plants and beasts inhabiting its crust to the “mold” and the “mite” infesting “cheese.”
The poet-scientist Goethe, in 1798, proclaimed that life seen from a high enough altitude looked “like a malignant disease.” Not unsurprisingly, Arthur Schopenhauer — the quintessential cosmic curmudgeon — went further, remarking in 1844 that biology was but a “moldy film” on a “cold crust,” hurtling through “endless space.” As the 19th century dragged to its end, the Parisian novelist, Anatole France, reiterated the same pondering whether our “tiny planet” had become “spoiled and rotten.” Maybe we were merely symptoms “of the disease which has corrupted this bad fruit,” he concluded: indistinct from “bacilli and germs,” “abhorrent to the universal order.”
Following the 1859 publication of The Origin of Species, Charles Darwin had begun convincing the world that complex creatures can’t spawn without ancient ancestries. But, initially, the reception focused on how Darwin’s findings seemed to confirm the ignoble nature of our pedigree. In Darwin’s eyes, after all, life’s cradle was some “warm little pond.” The many intermediating steps from protist to primate hardly severed the umbilical link to what Darwin emotionally referred to as our “lowly origin.” Nor did he pass comment on whether this same evolutionary process afflicts every planet feasible. At the time, many scientists assumed it simply must.
Just as, centuries earlier, it took incontrovertible evidence to prove we orbit the sun rather than the other way around, it took much countervailing evidence about the wider universe to determine that Earth’s organic infection might not be universal. For example, for generations, many eagerly believed Venus was a lush jungle planet teeming with life. This belief was only toppled when we sent probes there, revealing it to be a scorched hellscape with unimaginable pressure.
Indeed, coupled with the interstellar vastness revealed by progressively larger telescopes built throughout the 1700s and 1800s, science’s dilation of scale only inflamed the notion of our slime-born, terrestrial wretchedness. Not only were we mucus, but we were also both astronomically minuscule and, for all anyone knew, astronomically mundane.
By the early 1900s, practicing cosmologists — even ones of notably sunny disposition — were reproducing the motif, almost unthinkingly. In 1924, writing for The Nation, the Missourian astronomer Harlow Shapley speculated on how life began. He described how the sun’s “everflowing” barrage of energetic largess upon Earth’s warm ponds must have “aided” in complexifying compounds into protoplasm. At length, Shapley continued, “a green mold formed on spots on the planet … and here we are — parasites on the energy of the sun that casts us forth. How can we better the world?”
Sir James Jeans, another prominent practitioner and popularizer of cosmology throughout the early 1900s, put it less neutrally. Speaking at London’s University College in November 1926, Jeans wrapped up his lecture by explaining how recent developments in his field might reorient our view of life’s place within the big picture. As a passing rhetorical flourish, he reached for the now-familiar phrasing, asking whether we might look upon biology as “a disease which affects matter in its old age.”
Jeans was, however, perhaps the first cosmologist to decisively stress that life is almost certainly a vanishing rarity within the cosmos. In the same talk, he emphasized that recent breakthroughs in physics had made it apparent that “the physical conditions under which life is possible form only a tiny fraction of the range of physical conditions which prevail in the universe as a whole.”
This was largely based upon the discovery of radioactivity, which only a couple of decades before revealed a universe reverberating with life-destroying emissions. More importantly, radioactivity had also brought the shocking revelation that the Universe itself has undergone evolution: the clement conditions permitting complex biology are not only highly localized in space but have, far more importantly, only very lately coalesced in time. As Jeans authoritatively stated:
Life is the end of a chain of by-products; it seems to be the accident, and torrential deluges of life-destroying radiation the essential.
A Sticky Metaphor
Motifs and metaphors are sticky. What was a passing flourish for Shapley or Jeans becomes ingrained in popular science’s lingua franca such that a figure like Stephen Hawking still echoes it generations later. These metaphors can be hard to decommission, even after the theories that inspired them have long been dismantled.
The claim that “life is just slime” comes down to us from a time when, given the conviction that ludicrously complex creatures could spontaneously generate, it made sense to compare living processes to a cosmic putrescence or contagion. But we now know this assumption is wildly wrong, particularly when it comes to the remainder of existence, falling outside a relatively small shell extending several miles upward and downward from the Earth’s surface.
A backward glance might clarify why a string of purportedly atheist — even nihilist — thinkers would have felt demoted by the fact life is “just” scum on a rock. Clearly, they were retaining habits and hopes from inherited but not fully displaced outlooks, such as revealed religion, which promised humankind a special place in the universe.
Ballenstedt’s case is clearcut: as well as a paleontologist, he was a practicing pastor. This is why Adam’s spontaneously generating tapeworms fretted him so. But, even in the case of explicit unbelievers, the lingering influence of former outlooks still applies.
Even Nietzsche, amongst the first to announce the death of God in 1882, did not entirely escape this. In Also sprach Zarathustra, written between 1883 and 1885, he goaded that, if our planet can be said to have a skin, then “man” is but a skin disease. Elsewhere, he revealed residual Christian attitudes when expressing his revulsion that the “human intellect in nature has no further mission that would lead beyond human life.”
Nietzsche’s deflation here seems a hangover of the Christian assurance that there is some “mission” granted to humankind from on high by some impartial and omniscient guarantor. His disappointment indicates that, deep down, part of him still wanted this to be true. For, ultimately, one can only feel disinherited if one still believes, even unconsciously, that the universe “owes us” protagonist status.
But where else could an organism’s vocation begin than in its own backyard? To borrow Voltaire’s famous words, one must tend to one’s own garden. Bernard Williams also got it right when he asserted there is “no question of human beings and their activities being important or failing to be important from a cosmic point of view.”This doesn’t make the aims of the biotechnologist any less meaningful or vital. One doesn’t need some external guarantee to feel the impulse to improve or enhance one’s surroundings. Contributing to scientific understanding and application is mission enough.
Slime Moves to the Petri-Dish
Along with the waning of religious conviction and the growing understanding of the rarity of life in the cosmos, a new theory gained prominence: that life’s emergence on Earth may have been an event of happenstance. By the 1960s, writers were remarking we might do well to view life’s emergence “in terms of probability and chance rather than as the outcome of aim and effort.” But, as far back as 1933, the biochemist Frederick Gowland Hopkins — responding directly to Jeans’s “disease” comment — was already stressing that many of his colleagues were in agreement that “life’s advent” on Earth might stand as one of the “most improbable” events in the “history of the Universe.”
The accuracy of this, today, remains an open question for the fields of biology and astrobiology. Recent discoveries, such as the presence of organic molecules on the asteroid Bennu, imply that the building blocks of life might be commonplace. But the probability of the process leading from those building blocks to talkative and technologically adept mucus is a completely different question. What is certain, however, is that we can no longer bet on an abundance of beings “like us” in the universe. Of course, probability or improbability doesn’t provide any final criterion of worth. But we at least now know we are a cosmically endangered form of sludge.
Throwing this endangerment into further relief, the Doomsday Clock of the Bulletin of the Atomic Scientists, a metaphoric gauge of humanity’s closeness to global catastrophe, has never been closer to midnight. Yet, there will never be another chemical scum quite like us.
Though he didn’t tease out the implications himself, this was one of the more profound upshots of Charles Darwin’s discovery. Species are forged by unrepeatable histories, which tether them, in time and space, to their place of origin. Earth’s cheese mites, as well as its upstart simians, are therefore cosmically unique to Earth.
We now know we are descended from one unguaranteed furtive fruiting that may well not have persisted long enough to generate “its endless forms most beautiful.” Indeed, since roughly 1980, evidence has emerged that life has gone through several paroxysms — the so-called “Big Five” mass extinction events — which have decimated global biodiversity. The Permian-Triassic mass extinction wiped out upwards of 80 percent of all species then extant. Life, in other words, is fragile. This is a monumental shift from the ways people thought for almost all of history. Perhaps we should start acting and talking as if we took this to heart.
Our assessment of the organic ooze should encompass future possibilities, too. As the American cartoonist Clarence Day realized back in 1920:
This is no world for pessimists. An amoeba on the beach, blind and helpless, a mere bit of pulp — that amoeba has grandsons, to-day, who read Kant and write symphonies. Will those grandsons in turn have descendants who will sail through the void, discover the foci of forces, the means to control them, and learn how to marshal the planets and grapple with space? Would it, after all, be any more startling than our rise from slime?
Another of Darwin’s profound insights was that, of all the organisms possible, only a vanishing few will or can exist. This explains why life looks the way it does today: because a selection of organisms propagated in the past, to the permanent exclusion of other possibilities. Given a greater modern understanding of the building blocks of life, we understand that the space of all possible organic forms is yet vaster. There’s far more unrealized than realized, far more possible than actual. Perhaps in pursuit of such unprecedented forms, or in pursuit of more instrumental goals, future biotechnologists will pluck some of these exotic possibilities from inexistence, enriching our universe in ways that would otherwise never have come to pass.
Something like this was the hopeful vision of the French science writer J.-H. Rosny aîné, writing on plausible futures as early as 1889. Reflecting on the potential for a “synthetic biology,” he noted that many of the period’s ongoing technological breakthroughs from “electrolysis” to “radiophony,” possessed a surprisingly “organic” appearance. This, to Rosny aîné, signaled the possible arrival of “an era in which mechanisms, properly speaking, will disappear from our apparatus,” giving way to “appropriations” of organic forces.
Regardless of what lies ahead, there is already much to be proud of. The protoplasm in our skulls has begun modeling nature’s most fundamental laws: tuning into time’s beginning by discovering the Big Bang and forecasting physical processes stretching trillions of years into the future. This, roughly, was the retort of the physicist David Deutsch, responding to Hawking in 2005. Deutsch classified us as the “chemical scum that dreams of distant quasars.”
Recent science has begun increasingly to hold — against the historical default assumption — that Earth’s hitchhiking slime is not something that it’s easy for matter to become infected with. We might be mold, but we are an astronomically rare mold: categorically incomparable to our everyday experience of mildew, which effortlessly sprouts wherever it can. And given that we, alongside all Earth’s other species, are cosmically endangered this way, we should probably start thinking about conservation in a cosmic light too.
This would involve making Earth’s resident mucus more resilient to the risks it faces. In so doing, we would, after all, be tending to our own garden. For in our hyper-interconnected and hyper-technological age, that proverbial garden is now — whether we like it or not — the whole of our shared, living planet.
Thomas Moynihan is a historian and writer. He is a Research Affiliate at Cambridge University’s Centre for the Study of Existential Risk. His previous book was X-Risk: How Humanity Discovered Its Own Extinction (MIT Press, 2020), and he has written for publications ranging from the BBC to Big Think and the New Scientist.
Cite: Moynihan, T. “Life as Slime.” Asimov Press. DOI: 10.62211/48yf-17jk
Lead image by Ella Watkins-Dulaney. Collage Credits: History of the Olympics, Picturepoint, London / UN/DPI Photo / NASA / National Astronomy and Ionosphere Center, Cornell University (NAIC) / Frank Drake.
Artist’s Note: The images in this collage are from the Golden Record carried aboard the Voyager 1 and 2 interstellar probes sent into space by Nasa in 1977. They represent a snapshot of humanity and life on Earth. When I read 'Life as Slime,' I was reminded of the care that was taken to curate the Golden Record. I think this article and the interstellar time capsule share the same sentiment: life on Earth is precious and amazing.
Dizzying & dazzling
Thank you.