If we follow that model, humanity could exist for another 800,000 years.In that time, about 20 trillion people could be born.
The future of humanity seems insecure. Rapid climate change, political division, and our greed and failings make it hard to look at our species with a lot of optimism and so many people think our end is in sight. However, humans have always thought they lived in the end times and every generation assumes they are important enough to witness the apocalypse. This leads to short-term thinking and prevents us from creating the best world for ourselves and our descendents.
What makes this worse is that we may actually BE living at an extremely critical moment in human history. To understand why, let us look at the temporal window of humanity and ask: When will the last human be born and how many people will there ever be? These sorts of estimates come with a lot of uncertainties, so please take them with a gigantic grain of salt.
To get a sense of how many people there will be, let us see how many have already lived. Modern humans arose some 200 thousand years ago and they were uniquely good at making tools, telling stories, thinking abstractly, planning and working together in large groups beyond their close family. Still, there were not that many of us. Surpluses in food were sparse, survival was hard, and life expectancy was low. It took us 150,000 years to grow to a population of 2 million. Improvements were gradual and eventually led to the agricultural revolution, arguably the biggest change in our history. This was when our numbers really started growing. It took ten thousand more years to get to 300 million. But that increase was dwarfed by the industrial revolution. In 1800 there were a billion of us. The human population doubled in just 120 years and then again in fifty. Today, we number around 8 billion. In total, over the last two hundred thousand years about 117 billion humans were born and lived, and 109 billion also died. Which means that about 7% of all humans that ever lived are alive right now - as many as were born in the first 150,000 years of human history. Every minute, 270 babies join the party. But there are not just more people, never before have we been as healthy and well off, or lived longer. With growing living standards our birth rates collapsed. The UN estimates that around the year 2100 we will hit our population peak and there will be 125 million people born each year.
It is pretty unlikely that birth rates will stay stable forever, but let’s pretend to make our thought experiment simpler. How many people there will be in the future depends on when our species will die out. And here we find a lot of uncertainties. We are able to destroy ourselves through our own inventions, but we are also able to find solutions to avert catastrophic risk. We can change the direction of planet killer asteroids but we’ve also invented nuclear weapons. We discovered antibiotics but also carry diseases across the globe in a matter of days. Our industrial system gave us an incredible standard of living but also changed the atmosphere in the process. It is very hard to say if human ingenuity will prolong or shorten our species’ lifespan. If things go badly our end could come suddenly. But if we manage to avoid that, we could conceivably stick around for a long time. So every day we don’t destroy ourselves may mean life for an unfathomable number of humans.
How many people are we talking about? It depends on how far our species is going to expand. Scenario 1: Humans will never leave Earth. If we stay on our home planet, a good metric to look at is the extinction rate of animals that we get from the fossil record. The average lifespan of mammalian species is in the region of 1 million years, with some surviving up to 10 million years. Our close relative homo erectus survived for about 1.9 million years. If we follow that model, humanity could exist for another 800,000 years. In that time, about 20 trillion people could be born. Assuming humans will survive for a million years, with a stable birth rate of 125 million people each year, this would mean there are roughly 100 trillion humans waiting to be born - 850 times greater than the number of people that have ever lived. This would make everybody alive today only 0.008% of all people that will ever live.
Instead of putting us at the end of the chaotic mess that was our past, this would mean we live at the very beginning of something big - the start of the human story rather than the end. If we match the survival time of the most successful mammals, then our future numbers rise to 1.2 quadrillion people that have yet to be born.
If we don’t die out within the next few hundred years, then we could expand onto other planets or into our own artificial worlds. With resources and energy so abundant, we could try out different types of society and ways of life. An interconnected civilization spanning the solar system would create the basis of existence for an absurd number of individuals, orders of magnitude more than if we stick to earth, even if it only existed for a few million years.
As enormous as the solar system is, it is just one star system among billions in the Milky Way. If future people can colonize, say, 100 billion stars and live there for 10 billion years, while each generating 100 million births per year, then we can expect something like a hundred octillion lives to be lived in the future. This is a 1 with 29 zeros, a hundred thousand trillion, trillion.
We can spin this up even more. The Andromeda Galaxy will merge with the Milky Way, adding another trillion stars for us to settle. Red Dwarfs stay active for up to a trillion years and future civilizations might even find energy for their habitats around black holes. Our descendants may attempt to reach other galaxy groups, and the potential number of people that could exist is estimated to be a tredecillion. This number is likely to be underestimated by many orders of magnitude. If we divide the total energy available in a galaxy by the average energy needs of a single person, we can see that there are quadrillions of unborn humans that are at our mercy.
It is important to think about the distant future and why our presence is so crucial, as what we do now matters for all the people who do not exist yet. We exist at a highpoint of human history, with incredible possibilities at our grasp.
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