The Greatest Fluke of All-Time

All complex life—including humanity—owes its existence to a single accidental merger that happened just once in the history of our planet.

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I: Awe and the Accident

“Awe is the feeling of being in the presence of something vast that transcends your understanding of the world,” writes the psychologist Dacher Keltner. It’s an exquisite feeling that consumes us when we gaze at the majesty of soaring mountain peaks or the endless constellations of stars that prick through the inky darkness of the night sky. Other times, awe can overcome us, sparked by the more banal heroism of a parent’s daily sacrifice or the power of a striking, improbable coincidence.

When awe washes over us, we sense that we are part of something larger than ourselves.

And quite literally, we are. As humans, we too often see ourselves above nature, the perfection of life rather than an accidental outgrowth of it. In the closing passages of On the Origin of Species, Charles Darwin marveled at the astonishing explosion of complex life, leading inexorably over endless eons, to us, as we moved “from so simple a beginning” to “endless forms most beautiful.”

The beginning was, in fact, simple. But to arrive at those endless forms most beautiful—the flowers and forests, ostriches and octopuses, dogs and dandelions, hedgehogs and humans—we needed to get lucky. And not just any old kind of luck. We needed the kind of luck that, it seems, happens precisely once every several billion years.

Every living thing you see around you is derived from a single accident. Forget happy accidents; this one was euphoric. It fills me with awe. It’s the greatest fluke of all time.

And virtually nobody outside of science knows about it.

II: So Simple a Beginning

For hundreds of years, scientists have grappled with an intractable question: how did life begin? As early as the 5th century BC, the pre-Socratic Greek philosopher Anaxagoras proposed that life existed throughout the universe. Earthly life, then, was a stowaway, transported here by an errant asteroid or other celestial body, a theory now known as panspermia. Competing theories have abounded since, including that life arose in a primordial soup, or that it developed near the seemingly inhospitable conditions of a scorching deep-sea vent. The truth is this: we don’t know.

However, modern science has slowly and steadily chipped away at the apparent impossibility of life’s emergence. The more scientists learn, the more they realize that, as the eminent biologist (and my colleague at University College London) Nick Lane puts it: the origin of life “no longer seems as improbable as we once imagined, and probably happened much faster than we thought.” The emergence of life is beautiful, but it may not be as rare or unusual as was previously believed.

Once life arrives, it’s also far more resilient than originally thought. Bacteria, we now know, can survive buried miles below the surface, clinging to life in a chunk of rock. As Lane notes, some bacteria can even “flourish in the dry valleys of Antarctica, or freeze for millions of years in the Siberian permafrost, or tolerate acid baths and alkaline lakes strong enough to dissolve rubber boots.”

That growing scientific consensus leads, unavoidably, to a puzzle. If life can emerge repeatedly, and survive unimaginably harsh conditions, then why can’t we see it elsewhere beyond Earth? Why haven’t we been visited by aliens, and why don’t our telescopes ever seem to detect extraterrestrial forests?

Nick Lane has helped establish an answer to that question—with plenty of evidence to back it up. The emergence of life, it seems, wasn’t necessarily nature’s improbable bottleneck. Rather, the bottleneck came from the power plants within our cells. That microbial power plant makes complex life possible.

Here’s the magical, awe-inducing bit: complex cells that give rise to complex life, powered by a microbial power plant, emerged precisely once. We’re direct descendants of that singular, unique fluke.

Without it, we’d all be stuck as bacteria—and your ability to read this sentence, or my ability to write it, would be rather undermined. (If you’re ever feeling bored because there’s nothing on TV, remember that you only narrowly escaped from the dull existence of life as a bacterium).

Perhaps life has arisen repeatedly on other planets, popping up over and over across the vast endlessness of space. But odds are that most of it is stuck in simple mode, never evolving into the complexity of, as Darwin put it, “endless forms most beautiful.” That would provide a compelling answer to the puzzle; life abounds beyond Earth, but it’s mostly stuck at low levels of complexity, so it’s invisible to us.

If, as the name of this newsletter suggests, living life is like wandering through a garden of constantly forking paths, well, this was arguably the biggest fork in the history of life on Earth.

How did it happen?

III: Mergers and Acquisitions

About two billion years ago, two microbes bumped into each other, but one of them ended up shacking up inside the other. They produced an endosymbiont, which is the fancy biology term for an organism that lives within the body or cells of another organism. (If you want the technical detail, the working theory suggests that this microbial merger happened between a bacterium and a member of the Archaea lineage, a single-celled prokaryote).

What likely happened was strange, but miraculous. The bacterium set up shop inside the other microbe. The bacterium then became the mitochondria within the other cell. The powerhouse of complex life was born.

The theory suggests that this merger gave rise to the eukaryotes, a club that you’re a member of, even if you’ve never paid your dues. Eukaryotes are organisms with cells that contain a nucleus and other membrane-bound organelles. All animals, plants, fungi, etc., are eukaryotes. That decisive trait, about how our cells are organized, connects you to me, but it also connects us to everything from manatees to mushrooms.

In 1967, the path-breaking biologist Lynn Margulis proposed that our cells were the product of this kind of microbial merger. She was widely mocked, the punchline of jokes and behind-her-back snickers about fantastical junk science. But like many who had stubbornly gone against accepted wisdom before her, Margulis has been proven right. Genomic sequencing has helped to establish a strong likelihood that a single accidental merger gave rise to mitochondria, and by extension, every form of complex life on the planet.

As the science writer Ed Yong explains, writing in Nautilus:

The kind of merger that creates mitochondria seems to be a ludicrously unlikely event. Prokaryotes have only managed it once in more than 3 billion years, despite coming into contact with each other all the time. “There must have been thousands or millions of these cases over evolutionary time, but they’ve got to find a way of getting along, of reconciling and co-adapting to each other,” says Lane. “That seems to be genuinely difficult.”

Rather than being a gradual process, like so much evolutionary change often is, this was an event that apparently happened at a precise snapshot in time. (If it hadn’t, Earth might still be teeming with life, but none of it would be visible, nor would there be a concept of something being visible, because eyes wouldn’t exist).

IV: So what?

When astronauts go into space, they often report a profound shift in their mindset, as they see that the entirety of all Earthly life down below. This is known as the “overview effect,” in which they can’t help but see the big picture because the entire planet suddenly appears as a blue-green orb hanging in the dark emptiness of space.

But that feeling might be intensified even further if it were widely understood that everything living that they can see from the windows of their spacecraft, such as the vast rainforests of the Amazon, was only made possible by just two microbes that bumped into each other two billion years ago.

Why am I, a political scientist by training, writing about the evolution of mitochondria? There are two answers — one more banal, the other grander. The banal reason is that I find it fascinating. Every birth, every death, every war and invention, the entirety of the human saga, may be traced back to a microscopic evolutionary accident that has happened just once in billions of years. How humbling a thought!

But the more intellectual reason is that it highlights the uncertainty and messiness of life—not just of life in general, but of our lives. Everything we read tells us why something happened. The stock market plunged today because of an earnings report, or Trump became president because of a backlash against globalization. We crave simple explanations that fulfill two crucial criteria:

1. One identifiable cause produced one identifiable effect;

2. We know it to be true, with certainty, or can convince ourselves that we do.

The real world isn’t like that. Social science is an inherently flawed project because it too often requires meeting those two criteria even when it’s impossible to do so. Take the unimaginable complexity of life and cram it into a neat and tidy equation if you’re an economist, or a neat and tidy narrative if you’re a historian. We love the word because.

The origin of complex life on Earth, likely derived from the greatest fluke of all-time, reminds us of a profound but often forgotten truth: sometimes there is no because. Things just happen, often with extraordinary consequences. And occasionally, in those moments, all you can really do is marvel at it with a sense of awe, as I do when I contemplate that hidden hero that made our lives possible: the accidental mitochondria.

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If you’re interested in more on this topic, Nick Lane’s work is fantastic, and you can find more out about his many excellent books here.