We only wish for what we do not possess. At least humans throughout history have made sure they search for the unknown. Similarly, now the curiosity arises – how would human evolution have been if the atmosphere was anaerobic?

Scientific inquiry happened, and even explorations. For someone who has a bit of interest in the geology and geographical stuff, the anaerobic life forms astound us. Creatures which live underwater or those who are living thousands of meters beneath the earth’s surface at high pressures.

Even the mundane creatures like tardigrades, which snails eat, bring in curiosity to know how people might survive in places where we cannot survive. Places that are depriving oxygen are the anaerobic conditions.

Human evolution
Image By: adrenalina/unlimphotos

To answer a question such as the alteration in the route of human evolution, we must ask what it means to be a human, which would take philosophers several millennia. Hence, we hop on to the second-best idea. Draw arbitrary lines of the evolution process.

What is a Human?

A human is a mammal, has organs and is an intelligent life form. Indeed, the definition does include many species in the bracket. Still, if humans were to persist in spaces where we naturally do not, the definition of’ human’ would fundamentally change anyway. Doesn’t sound like a good idea, either.

The third option is to compare the modern human to what would the anaerobic human be like while maintaining as much similarity as possible. It’s going to be a hell of a roller coaster!

One more aspect to consider. Water is a molecule made out of oxygen, and anaerobic lives are only a few on this earth compared to aerobic ones. Even the fishes have aerobic respiration because their gills use oxygen in the water.

While we can twist the word “anaerobic” in the literary sense to include life underwater, it cannot happen for two reasons:

  • It’s scientifically unacceptable. Just not possible!
  • There are not many options of humans evolving into some other creatures except being something like whales, dolphins and their relative species.

Here’s how things would have been. When we stretch back our lineage to the very point life started, it was only prokaryotes.

Anaerobic Condition 1: If We Were in Water

The prokaryotes evolved into eukaryotes, which further evolved into worm-like creatures that could only wriggle to swim. We developed the spine, brain, and organs and finally became a Placodermi.

This Placodermi took several million years and evolved into the Aganthostega, a segue to the amphibian stage. Aganthostega was primarily a creature which surrounded the shores and occasionally found itself on land, only to return. Constant efforts of the Aganthostega to evolve led them to become Westlothiana, the first amphibian.

It’s a good start, but we still lay eggs! That needs to change. We evolve to an identified yet unnamed placental mammal, the common ancestor of all mammals. Most creatures relinquished the external placenta or pouch as they evolved, save for a few, like kangaroos.

Placental mammal
Image By: adrenalina/unlimphotos

It was necessary and a better evolutionary trait than most reptiles who laid eggs or other mammals that could have their babies stolen. This unnamed placental mammal ventured into the forests while few found their niche on shorelines. The ones who found their niche on the shores evolved into the Peregocetus pacificus.

The Peregocetus pacificus had a large snout like a gharial, had four legs and a shape much like a lizard. It would grow as large as seven or eight feet long and swim across the waters close to the shores. It also didn’t hesitate to take deep dives while keeping its mammalian trait intact. Fish might face a problem getting picked by birds on the surface, but not this giant.

There was no gravity in water, so they found it easy to catch all the creatures on the surface and grow as much as required. They travelled deeper into the oceans, and they essentially evolved in a reverse direction as their hind legs disappeared in a few million years. At this stage, they were known as Dorudon.

Their size grew more extensive, and they became Basilosaurus, a kind of underwater dinosaur which ventured into larger territories and dominated the ocean, shifting their chief source of food to phytoplanktons. A more significant size needs a more extensive diet to sustain, and there wouldn’t be many fishes left if they were to thrive on other creatures alone.

Basilosaurus were around 18 metres in length, nothing close to the largest mammal ever existed, i.e. Blue Whale, 24 metres long. Blue Whales belong to a group of families called the Cetaceans, including the dolphins.

A slight change in the location is how drastically human evolution would impact us. Now, whales are the only aquatic creatures that possess some intellect, mammalian anatomy, etc. Still, there are oodles of differences outnumbering a handful of similarities.

Imagine the change if it was down to the primary manner we respire!

So, what would anaerobic life be like? For that, we need to know where on earth, do we find anaerobic life?

Minuscule marine animals live in the absolute depths of the ocean, where they complete their life cycle without the sight of life. They are found in the unforgiving temperatures of volcanoes too. There are several areas where anaerobic life thrives. There are bacteria which operate in muddy areas thriving in the absence of oxygen.

Deep Water Anaerobic Human

Deep Water Anaerobic Human
Image By: Alex Aleksei/unlimphotos

Let’s carry forward the idea of a whale to the point that humans settle at the base of the ocean floor or, more importantly, places where we have no light. Places where pressure would be several times that on the surface. Life like a mermaid!

There would be no food in the deepest places on our sea floor. If we go deeper, we would be unidentifiable from any fish, and any speck of our mammalian living would be long gone. Hence, the whales would have to reduce in size in a million years of evolution to survive. We must have noticed how the cetaceans have shortened their jaws en route to their current status.

You see, our mammalian identity marker is having babies. To have babies, we would have to travel kilometres above the surface, make distance across uncharted areas – only to give birth to our offspring in a distant land. It would either mean having a high-functioning set of lungs or going extinct.

The most probable situation is both. The development of alternate gills isn’t something odd that we would see. However, we improvise across many hundreds and thousands of years with evolution.

In fact, after seven or eight million years, even those lungs would be non-existent since the creature wouldn’t need them after living in deep, dark depths. Humans may develop bioluminescence or split up our legs into extra pairs of limbs like the octopus.

While it does appear outlandish to read such things in articles, it may become a choice. Without light, we would also reduce the human to a transparent creature without bones. In such a depth, we would not even require bones. It is because the insurmountable pressure from the oceans is an ability.

But wait, there is one thing we may not lose. The ability to have an external placenta. While mammals give birth to babies, we may turn into the likes of platypus. Although it’s only in name, we would appear more like a blobfish or other creature walking across the sea floor. Only a deep oceanic, colourless, hairless, legless version.

Anaerobic Condition 2: If We Lived Underground

Talking about the sea floor, becoming an anaerobic creature would open the door for humans to exist everywhere – even if they do not need the required elements to survive and make their presence felt in the everyday world. In such a scenario, we might as well ask, what if humans lived in caves like rats and finally lived as underground animals to evolve into something?

First of all, this strategy wouldn’t work. We would have to dig far larger holes than conventionally available to live in caves. It would also mean using our fingers and gaining on claws rather than thumbs as we evolved.

Underground human claws
Image By: Yaopey Yong/Unsplash

We wouldn’t compromise our ability to hold, but instead of being on trees where we are safe from several creatures which cannot ascend, we would be in danger of getting killed. We wouldn’t survive long enough to become creatures that would live underground, but let’s throw the logic out of the window.

Let’s imagine humans continue to survive all these years as underground creatures, fighting off dangerous stinging insects and snakes. Humans would have the ability to see in the dark!

If we lived underground, instead of being agile, active and running on the surface, we wouldn’t spend most of our time sitting or sleeping all curled up. That’s one plus point that we would have. We would also learn to go all in and create an underground network of dwellings, but we will shrink in size in thousands of years.

For thousands of years, we would diminish to the size of rats and smaller insects and create wide networks through the deep underground, just like roots. It would occur since we would be utilising our brains specifically for this one trait we have mastered, much like termites.

Since we have a longer evolutionary story – we would also be accustomed to various toxins emitted by underground creatures. Plus, our specialisation would lie in creating underground networks which spread from the ground level to the crust. Human muscles can respire anaerobically when subjected to intense workout sessions. That’s how we create lactic acid in our bodies.

Instead of oxygen, we would require anaerobic respiration and, in essence, over a hundred million years – humans would be no more than just bacteria which help organic farming. With a few added features which would be insignificant given our size. A pretty dead end!

Anaerobic Condition 3: If We Lived in Volcanic Territories

Volcanoes are territories usually avoided by most, except for particular mountainous creatures, birds and bacteria. However, bacteria develop in such areas – so why not ask the same question there?

Image By: Tanya Grypachevskaya/ Unsplash

Along with pressure, we also have two new things to face here as follows. 

  • The extreme amount of heat in the peripheral areas of the furnace-hot magma reaches temperatures above 1000 degrees Celsius. 
  • The extreme pressure of about 100 kilopascals equals 400 times the normal atmospheric pressure.

The very first possibility is that our skins would begin to harden. We would begin defying hotter temperatures and higher pressures. We would turn into animals that specialise in living temperatures that cross fifty degrees Celsius, much like the desert scorpions.

Humans would develop exoskeletons which can withstand heat up to several degrees. Quite possibly, exoskeletons can protect us from boiling water! Like all other hostile playgrounds discussed before, even this would have a damning effect on a human’s height and weight.

These exoskeletons would also spawn the humans to shorten and lighten over time, passing through areas vulnerable to other animals. The presence of sulphur and various carbon oxides in the surroundings would also bear specific reactions on human evolution, which was undiscovered before.

In a hundred million years, we would be, at worst, a multicellular being which exists in these conditions like bacteria. At best, we would become a beastly animal forged by molten iron, which we only heard of in fantasy tales.

Natural Development

Evolution is just luck for animals, over significant periods, due to the tiny decisions they undertake. For example, we can look at the Bajau people of South-East Asia. These people have always lived on houseboats and spent close to twelve or thirteen hours at sea, often restricting their breath for minutes. A study of the Bajau people found that everyone has evolved a spleen larger than most human beings would naturally have – just due to their lifestyle.

Stillhave we ever believed why we are wired to suppose in a manner to believe we should be mammals and have specific characteristics to pass as humans? Or at least having a body part with a close semblance to humans?

Image By: Helena Lopes/ Unsplash

What if our lungs were designed to be used by nitrogen and not oxygen? Much like some trees absorb harmful air pollutants. Or something similar to a machine. We need not work with our traditional knowledge for such an outlook but look at the future. For a basic, developing economy to flourish, it needs industries to manufacture several things, and tech manufacturing is currently at its peak.

Robots and other AI-based assistants are ever more a part of our daily life. The day is not far when AI-based individuals, carrying humanity as a module and set of rules, start creating new life forms – or new mechanical individuals, which may need new fuel – and nitrogen looks like the proper aspect, which is available in abundance.

From our skin colour to our skeletal systems would be very different, but how different can it be? Our skin would be made of pigments which do not react with nitrogen at any cost. But what kind of material?

It might be metal, but I would bet on a compound that we may know now – but would appear funny if mentioned in this century. Our skeletal systems would also have elements more vital than just calcium. Perhaps, we may walk with titanium in our bodies, strong enough to survive even the worst of jolts and making us accident proof!

Out of the World – a Possibility of Anaerobic Life?

When we look at the future, we cannot miss out on human’s possibility to venture to other planets and moons. It would certainly be a leap forward for humanity but would humans evolve anaerobically on such heavenly bodies? We do not know.

Yet, we know that staying in space can cause several effects on ourselves. Our bones begin to weaken, and our height enlarges due to the lack of gravity. The lack of gravity also causes several side effects such as motion sickness, vomiting, nausea, etc.

Space has radiation levels which are far from hazardous by human standards. Radiation in space even happens through subatomic particles as they tear through DNA molecules. It can cause cancer in humans, but evolution would weed that out. As humankind has a future in space, they are likely to grow beyond such side-effects of being in space.

Image By: Mike Kiev/ Unsplash

Lastly, space is cold enough to reach absolute zero at times. In the next thousands of years, various rockets may fail, and we humans will visit various ecosystems that are not ours. As we tend to terraform various planets, we note that not all planets have an atmosphere.

Cryptobiosis is when an animal switches to a comatose state when exposed to intense cold, using little to no energy to survive. The animal remains in a cryptic dead stage until the temperature returns to favourable conditions. Some planets are as cold as space for the same reason. Millions of years in, and it’s possible we see humans adapt to cryptobiosis. 


Humans could have been anything else than the current species we are. The outer world is a box of infinite possibilities, and the evolution of humans will undoubtedly undergo an enormous change in the immediate future if we keep up our spirits to discover more beyond the earth.

If you liked this article, check out: The World Without Cars: A Sustainable Future.


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