In a recent interview with Joe Rogan, Elon Musk said building a city on Mars was a necessary step to safeguard the future of human civilization—citing the potential threat of humanity “dying in adult diapers.” He says:
“Can we make Mars self-sufficient before civilization has some sort of future fork in the road where there’s either like a war, nuclear war or something, or we get hit by a meteor, or simply civilization might just die with a whimper in adult diapers instead of with a bang? I think we can do this. [...] We should just make sure that we extend the light of consciousness to Mars before civilization either extinguishes or subsides. All that needs to happen is that the technology level of Earth drops below what is necessary to send spaceships to Mars. So, if there’s some really destructive war or, like I said, some natural cataclysm, or simply the birth rate is so low that we just like to die in adult diapers with a whimper—that's one of the possible outcomes for a lot of countries.”
Musk goes on to cite the exceptionally low birth rates of some developed nations, such as Japan and Korea. He says:
“At current birth rates, in three generations, Korea will be about 4% of its current size. [...]
Maybe even less than that. They're only at 1/3rd replacement rate. So if you have three generations, that's 1/27th of your current population, which is 3%.”
Musk paints a dire outlook on human population levels—something he has mentioned before. But are his fears warranted? Here’s how this evolutionary biologist—who has spent time researching population dynamics—sees it, in three concise points.
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1. The World’s Population Has Exploded Over The Past Century, And Will Continue To Grow
The global population has grown from 2.5 billion in 1950 to 8 billion today.getty
For the first time in human history, the world’s population reached eight billion people in 2022. This is mind-boggling when you consider that the population was only 2.5 billion in 1950 and seven billion in 2010.
Not only that, the human population continues to increase. According to U.N. projections, the world could reach a population of approximately 10 billion people by 2050 and even 10.5 billion by the mid-2080’s.
It’s probably the case that overpopulation is a more pressing issue than under-population.
2. Population Growth Appears To Be Slowing—But That Doesn’t Mean Humanity Is Doomed
For the majority of human history, population growth has been just barely positive. To be precise, from ancient times until the start of the Industrial Revolution, global population growth averaged only about 0.04% per year. However, after 1800, the growth rate picked up dramatically, reaching its highest point of about 2% annually in the 1960s. Since then, a global decline in fertility rates has caused the growth rate to decrease, but it’s still positive.
It is true that certain countries, mostly highly developed countries like Japan and South Korea, have real problems with population decline. But, as a whole, humanity is doing quite well.
We see these types of dynamics play out in the animal kingdom all the time, where a species is on the decline in a certain region but growing globally.
A striking example is the Florida panther, the last remaining puma population in the eastern United States.
Once abundant, now endangered in the U.S., the Florida panther faces a fight for survival.getty
Pushed to the brink of extinction due to habitat loss and human persecution, the Florida panther is federally listed as endangered under the U.S. Endangered Species Act. However, the puma species overall, Puma concolor, is the most widespread land mammal in the Americas, ranging from Canada to Patagonia.
With stable populations across much of this range, the puma is classified as Least Concern by the IUCN Red List, indicating a low risk of extinction. The Florida panther’s plight, while serious, represents a localized conservation challenge rather than a crisis for the species as a whole.
A similar case is the Scottish wildcat, a critically endangered population of the European wildcat (Felis silvestris). Once widespread across Britain, the Scottish wildcat now survives in small, fragmented populations due to habitat loss, hunting and hybridization with domestic cats. Despite its dire status in Scotland, the European wildcat species as a whole remains relatively secure, with strongholds across mainland Europe. Like the Florida panther, the Scottish wildcat exemplifies how local population declines do not necessarily indicate a species-wide threat of extinction.
3. Population Decline Is A Solvable Problem
What makes the adult diaper theory of population decline even more dubious is that it seems to be more “solvable” than other issues that might threaten the existence of humanity. In other words, governments have a certain amount of control over whether this number trends up or down—for instance, by offering incentives (like a child tax credit) for having children.
Again, the natural world holds numerous examples of how smart policies aided in the recovery of animal populations.
Let’s turn to the Florida panther yet again—by the 1990s, its population had plummeted to fewer than 30 individuals, with severe threats from inbreeding and roadway fatalities. Recognizing these challenges, conservation biologists introduced individuals from a genetically similar puma population in Texas, increasing genetic diversity and improving offspring survival rates.
Additionally, the construction of wildlife corridors helped reduce roadway mortalities, further aiding in population recovery. Thanks to these efforts, the Florida panther population has now rebounded to approximately 200 individuals.
Similarly, Scottish wildcats are benefiting from targeted conservation interventions. Captive breeding programs have been established to safeguard the population, while conservationists are also addressing a more complex challenge: hybridization with domestic cats.
Efforts are now underway to “rewild” the Scottish wildcat genome by selectively breeding individuals with minimal domestic cat ancestry, with the goal of restoring a genetically pure and self-sustaining wild population. These examples highlight how proactive conservation measures can reverse population declines and prevent regional extinctions.
The adult diaper theory, though cleverly named, is at the bottom of my list on how humanity will ultimately extinguish itself. What’s more, protecting the future of humanity by making it a “multi-planetary” species, as Musk proposes to do, seems like a riskier bet than working to preserve the delicate ecosystem of our home planet.
Perhaps more than the adult diaper theory of population decline, climate change has the power to change demographics. How worried are you? Take the science-backedClimate Change Worry Scale to know how your fear compares with others.