A Tenuous Thread
During the time from one million to a half-million years ago, we know from genetic evidence, the total population of humanity was not much more than 50,000 individuals alive at a single time. This is about equivalent to the population of the remote, icy wasteland known as Greenland.
This meager thread of humanity was speckled across a vast wild area in eastern Africa, as isolated bands and villages of perhaps a few dozen people. Imagine never meeting more than a hundred people in your entire life — and imagine that if you did, you'd have met a sizeable fraction of the entire human population of the Earth.
They lived precariously, hunter-gatherers in a world of brutal subsistence poverty, at the mercy of the climate and the migrations of animals. There were often good times, and the people were happy. But if rains didn't arrive on schedule, entire communities might be wiped off the map by starvation. And humanity was far from united in its struggle against the elements; opposed bands of humans must have often fought and raided each other. Looking back, we can feel the absurdity of it! Just fifty thousand people on the whole planet, but nevertheless: "this valley ain't big enough for the two of us"! But these were desperate times, and the struggle for life must have been fierce.
Incredibly, humanity's population numbers seesawed back and forth around this terrifyingly low average for literally thousands of generations. We walked this tightrope for fifty times longer than all of recorded history: neither crashing to extinction nor taking off in the flowering of exploration and growth that would come later. Instead, it took every exertion of effort merely for the people of the ancient grasslands to maintain a toehold on the edge of existence.
These struggling people could never have imagined the fantastical, glittering civilization that hung in the balance of their every action. Imagine it like a ghostly presence of all the Earth's greatest metropolises: invisible towers and houses and roads and churches and bridges hanging all about the world like a mirage. Imagine it flickering brighter or dimmer with each new twist in the uncertain prospects of this odd, struggling species out in the grasslands. With every momentary, hard-won advantage in the struggle for life, things in the savannah would get just a little bit more stable and prosperous, and that fantastic ghostly vision would come just a little closer. Hanging gardens of Babylon materializing in a shimmer of desert air; all the roads to Rome tracing secret paths under the wild forests of Europe like the roots of a great tree. Those ancient humans' actions were already a dire game of life and death. But in the uncertain flickering of this utopian vision, we see how the stakes of their lives were impossibly greater than they could have ever known.
A Time of Perils
Our modern genetic tools can't detect population bottlenecks shorter than a few generations, which impedes our ability to study disasters and collapses followed by a quick bounce back. But at the nadir of the human population curves, in the midst of an intense Ice Age around seventy-five thousand years ago, humanity was dealt a blow by the largest natural disaster of the last million years.
The detonation of the Lake Toba Supervolcano released more than ten times the energy of the largest volcanic eruption in the history of recorded civilization, and more than forty times the energy of the largest hydrogen bomb ever constructed by mankind. The unimaginable quantity of ash it launched into the high atmosphere caused an instant crash in global average temperatures of around six degrees Celsius — this is the same magnitude as the absolute worst-case scenarios of climate change by 2100, but with its onset compressed into a single year. Rainfall around the entire world fell by a quarter.
The trees and grasses of the savannah must have given way to a withered wasteland. Streams and other drinking-places would've dried to dust. For five years or more, the ash would've circulated in the atmosphere, shrouding the earth. The feebler sunlight that managed to filter through this layer would've taken on a smoky, reddish-orange glare.
Imagine the devastation this would've brought to a fledgling primate species already barely hanging on to their place on the savannah. Imagine wandering through barren plains searching for sustenance. There has been practically no rain all year, and it is now the coldest winter you have ever known. You trek for days without food, having abandoned your homeland to make a desperate gamble that something better waits beyond the horizon. As you walk, ashy dust specks drift in the air, and — with the ozone layer badly damaged by aftereffects of the eruption — a toxic sun stabs into you, burning your raw skin and causing painful damage to your eyes.
In the years after the eruption, famine would have swept across the terrain like a dry wind. With each life expired, the thread of the human story frays a little more. Many must have given up hope for survival.
As they do, the ghostly skyscrapers of Shanghai and London dissolve into empty sky. What seemed like a vision of great ships carrying food and goods across oceans, fades into the shadows of passing clouds, a trick of the waves and the light. The voices of billions of unborn future generations are urging on our struggling wanderer, prayers in countless languages are seeking blessings of safe passage for them. Survive this ordeal, and someday the countless flowers of humanity's latent potential will bloom: all the richness of earth's cultures and peoples hang in the balance, the thousand-year histories of art and exploration and simple joy at the vivid experience of being alive. All the hopes of history are pinned on this: our wanderer must find a way. Death now would be death eternal — an empty universe, the vision of glittering city lights fallen away forever into the blackness of night.
A Look in The Mirror
Our species survived that time of perils. All of us owe our lives to the suffering and ingenuity and dedication of ancient humans whose names we'll never know, who persevered even when frightened and hungry and confused, even when all seemed lost. The impossible dazzling vision has manifested: for every individual human that struggled through the Toba catastrophe, there are almost a million people alive today. And how well they live! They inhabit every corner of the earth, travelling swiftly between distant lands as they conduct every kind of business. Many of them live fantastically long lives: sixty, eighty, over a hundred years! They have uncovered countless of the deepest secrets of nature, which they use to create technological magic that ends disease, eliminates labor, and conveys them infinite knowledge on every subject. To the humans of the ancient savannah, our modern world is an age of miracle and wonder beyond imagining.
But just as the past is long, so too is our own future. After surveying the tenuous path that humanity has taken to reach this point, we must now turn around and ask ourselves what lies ahead. What unseen utopias shimmer in the air above our heads? Can we perceive the soaring towers, the lush gardens, and other astonishing artforms, constantly flickering with the uncertainty of all future hopes? Perhaps we can make out glittering lights on the moon and planets. Maybe even trails of points in the sky, like cars on nighttime highways, caravanning to distant stars. Feel the bustle as people of every future nation and culture come and go. Inevitably, it would be a diversity and richness so much greater than the peoples of earth today — what is it like when they laugh, or cry, or gossip among friends? What do they still wonder about, even with all their godlike knowledge?
Just as it was for our ancient wanderer seventy-five thousand years ago, the latent potential of humanity is still unimaginably vast and dazzling for anyone living today. But it is also uncertain, for we today are also living in a time of perils.
This time, we're strong enough to survive a supervolcanic eruption, or most else that nature might throw at us. But the danger is actually greater than ever, and it comes primarily from ourselves. Will our species find ways to cooperate and cool the tensions of rival nations, escaping destruction wrought by terrifying weapons of war? As we grow and learn, will we be wise enough to foresee dangers posed by new technologies, whose consequences are by nature unpredictable? Wandering through the uncertainty of unfolding events, how will humanity maintain sufficient control over our common destiny, ensuring we can steer towards the distant light of that optimistic vision?
With every twist and turn of fate, a grand future flickers in limbo. Listen to the rustling of the wind — can you make out faint trillions of voices, cheering you on, crossing their fingers that you'll help bring substance to the bright, invisible future all around you?
A Call to Action
Effective Altruism is a movement devoted to studying, prioritizing, and solving humanity's most pressing problems, including extinction risks from both natural sources (like supervolcanoes and asteroids) and from ourselves (like nuclear war, pandemics, or unaligned artificial intelligence). To learn more about the study of "existential risks" and what you can do to help civilization overcome them, you can:
Explore this list of what experts consider some of the world's biggest risks. It's full of links to pages describing each problem in more detail and explaining how, depending on your personal skills and background, you could use your career to work on solutions.
Read "The Precipice", a fascinating book by oxford philosopher Toby Ord which summarizes the state of our scientific understanding of different risks and investigates potential solutions.
Listen to the 10-episode podcast course "Effective Altruism: An Introduction", which explores the detailed philosophy behind the quest to do as much good for the world as possible, and interviews leading philanthropists giving away billions of dollars to EA causes.
Explore this very Forum! It's the premier destination for participating in the latest research and discussion of Effective Altruist ideas.
Genetic studies identify a population bottleneck with an "effective population" of 10,000, but this is a mathematical abstraction which translates into a real-life "census population" of around 50,000. For more detail on how ancient populations can be inferred from genetics, see this paper. ↩︎