What If Humans Were the Only Living Things on Earth? | Unveiled

What if Humans Were the Only Living Things on Earth?

So far, Earth is the only planet in the universe that we’ve found to host life… And, remarkably, it has it in abundance. It’s hard to fathom just how much biodiversity our planet truly holds, but the 7.5 billion human beings only make up about 0.01% of the mass of all life on Earth. How different would things be, then, if that figure was 100%, instead?

This is Unveiled, and today we’re answering the extraordinary question; what if humans were the only living things on Earth?

First, what constitutes a “living thing” in this question? Because the vast majority of life on Earth is actually plant life. According to a 2018 study on biomass distribution, published in the Proceedings of the National Academy of Sciences; our planet hosts 450 gigatons of plants! That’s compared to around 2 gigatons of animals, including just 0.06 gigatons of humans. So, in the most extreme case, we’re erasing every single piece of organic matter, besides humans.

Second, what constitutes a “human”? In this case, we’re imagining that the world is somehow instantaneously reduced to modern humans only. Human evolution has still played out in the same way, with all earlier iterations of humans - Neanderthals, for example - living on an Earth rich with biodiversity. It’s just us, the twenty-first-century human beings, who find ourselves suddenly having to survive without every other organism.

Unsurprisingly, this is one alternate world that would get very gruesome very quickly. Without any other food source to speak of, there’d be 7.5 billion people now facing a choice between starving to death or cannibalism… with anyone refusing to resort to the latter also faced with having to outrun anyone else desperate enough to try and kill them. It’s something which isn’t as abhorrent in the natural world as it obviously is in human society, with animals like lobsters and spiders all frequently eating each other… but it’s bad for humans for more reasons than it just being morally reprehensible. One case study focuses on the Fore tribe in Papua New Guinea where, up until the 1950s, members consumed the brains of their deceased. But the practice caused an epidemic of kuru disease, a severely aggressive neurodegenerative disorder. The Fore people abandoned the tradition when the link was discovered, but we’d see this (and problems like it) frequently appear in a humans-only world. Planet Earth suddenly becomes a dangerous and bloodthirsty battleground.

That is, unless we could very quickly adapt to eating rocks. Science doesn’t yet definitively know of any creature that eats rocks and actually gains nutrition from them… but the shipworm Lithoredo abatanica - a type of clam native to the Philippines - has been found to apparently consume and digest rock while it burrows into it. Whether or not the creature gets any actual food-like goodness when it does this is still a point of study… but the behaviour provides at least the faintest of faint hopes that this alternate reality needn’t be quite so gory. But, regardless of the way in which anyone tried to survive, it’s very clear that beyond a few days (possibly a few weeks) they wouldn’t. Just with food alone, the human body requires at least a semblance of balance between a list of key ingredients - vitamins, minerals, fats, proteins and so on - but it’d now be impossible to get even close to the correct nutrition.

The other big problem in a world without even plants is that we’d also lose our chief oxygen supply. Probably not before most would starve to death, but eventually. And that could not only kill off the humans that did remain, but also ruin the chances of life developing on Earth in the future. Equally, without plants for photosynthesis, we’d also have no way to remove carbon dioxide. Again, the atmospheric change wouldn’t be instant, and humans will likely have died of other causes before it becomes toxic, but an untapped, unrelenting blanket of CO2 does not bode well for Earth’s future, either.

If, in our hypothetical world, seeds are preserved… there could yet be a way for humans to save themselves; the Svalbard Global Seed Vault - or other facilities like it. The Vault stores seeds from around the world in case of an apocalypse or extinction. And this would be the ultimate in extinctions! Fast-thinking humans could use the Vault to repopulate the Earth’s plant life in a worst-case scenario. But, even then, time wouldn’t be on our side… with starvation setting in long before anything edible actually grew.

For a comparatively less bleak outcome, we can imagine what kind of world we might live in if we don’t count plant life among the things we’d lose… Though still tough, it’s a much more manageable outcome where the majority of humans survive and general life on Earth could still thrive.

If, like in the plant-less scenario, all the animals disappear instantly, it’d obviously mean that meat, dairy and animal products would be off the menu. The entire world population would find itself pushed into a vegan lifestyle… and, over time, the very make-up of a human being might even adapt into something which doesn’t just choose not to eat meat but actually can’t anymore. We’d be forced to evolve, to turn herbivorous, thanks to the incredible change in our environment… but at least it’d be an improvement on hunting each other or trying to eat rocks! In this world, our farming and agriculture industries would still exist, but they’d also be different - with no more livestock to contend with. Household pets would be a memory saved to history, and almost all natural habitats - every single ecosystem - would be in some way changed without the presence of animals and with human beings’ increased reliance on plants.

Again, though, a lot depends on where the line is drawn… because worlds with or without bacteria are two very different places! Eliminating bacteria and viruses sounds like a good thing; perhaps leading to a germ-free time when no one gets sick. But, actually, the trillions of bacteria that exist on Earth aren’t all bad - most of them are vital for life. The human body, for example, is crammed full of good bacteria which helps facilitate things like digestion. True, if bacteria were to disappear then we’d never see huge outbreaks of contagions like the Black Death, Smallpox or Tuberculosis ever again… but we also wouldn’t be able to function as living organisms ourselves. In this way, the natural world exists in balance. We’re one part of it, but we’re here because of countless other parts - and to switch to an environment that’s 100% human or anything else would be catastrophic.

As unlikely as this scenario sounds, however, we could encounter one quite like it very soon; on Mars. If and when we venture to the Red planet, as far as we know we’d be the only living thing there. Naturally, it’s not exactly the same situation, because Mars-bound astronauts would also carry with them food and oxygen supplies… so there’d be no need for the most macabre of survival tactics, and we needn’t just wait for evolution to gradually take its course. On Mars, we would be able to in some way control what happens to us. But, in terms of living as an isolated species, any mission to any other world would give us an unprecedented insight.

Back on plain old planet Earth, though, if every living thing which wasn’t human suddenly disappeared, we’d be in a world of trouble. If everything that wasn’t human or plant life disappeared, we’d have to adapt to become a fully herbivorous species. But if bacteria also upped and left, then we could - very quickly - cease to even function. And that’s what would happen if humans were the only living things on Earth.