Could Intelligent Life Evolve Underwater?
All life needs water. Because of this, it is no surprise that life on Earth began in the depths of our primordial oceans, possibly as long as 4.2 billion years ago. These prokaryotic microbes eventually evolved into multi-cellular, complex life forms, some of which could harness the power of the sun to fuel their continued survival and evolution. These photosynthetic life forms not only saturated the atmosphere with oxygen for animal life to evolve, but also moved onto land, providing those animals an incentive to follow. After millions of years of extinctions, environmental change, and evolution, a group of prehistoric primates finally succeeds in mastering the arts of fire, weaponry, and simple communication. Humanity is born.
Despite the fact that life existed in the ocean for billions of years before it ever moved to the land and that 75% of Earth’s surface is covered in oceans, intelligent life still chose land as its evolutionary stomping grounds. Humanity isn’t unique in this respect. Of the estimated 8.7 million species in existence on Earth today, only about 20% of them are marine dwelling creatures, meaning that 80% of Earth’s biodiversity exists on just 25% of its surface. This is due to the fact that marine environments are much less diverse, and change less readily than land environments. This environmental resistance to change stunts the evolution of marine-based life, only notably diversifying it over the course of hundreds of millions of years.
In the search for intelligent extraterrestrial life, we expect the same general principles of evolution to hold true for other planets like Earth on which life evolves. But therein lies the problem; no planet is exactly like Earth. Since the launch of the Kepler Space Telescope we have discovered thousands of new planets, not one of them exactly identical to our third rock from the Sun. One of the most commonly identified class planets which is being discovered actually has no analog in our solar system: the super-Earth. Super-Earths are multiple Earth-mass monsters which found a way to curb their incessant hungers before bloating themselves into gas giant planets. Because of their large masses, super-Earths are likely to be topologically quite flat, their immense gravities working to tear down any mountains or fill any canyons which attempted to form. If such a world were in the habitable zone of its host star, this flattened terrain would become an ideal bed for expansive, shallow oceans to form. In some cases, these oceans could completely encase the planet.
What, then, is to say about the evolution of intelligent life on such a “water world”? Or the potential for intelligent life in the subsurface oceans of tidally heated ice moons, like Europa or Enceladus? We believe that life has a chance to evolve in such places, but could it ever evolve to the point that it could learn, communicate, and invent? To answer this, we’ll have to take a look at why the human race became the prevalent intelligent species on Earth. Using us as a template, perhaps we can draw some conclusions on whether or not a race of intelligent life could ever evolve in the depths of an alien ocean.
Becoming Intelligent
For a species venturing to attain intelligence, a few important criteria must be met. The first of these criteria is large size. In the grand scheme of life on Earth, humans are pretty large. We are not the natural top of the food chain, but we are big enough to find ways to defend against the large, hungry predators that are. This allowed our race to survive and evolve long enough to gain intelligence, which may not come as easy for a species of smaller stature. A species of rodent, for example, could probably never gain intelligence because even if they had the brain capacity to communicate and sharpen sticks, they could never defend against a saber-tooth tiger or a gray wolf perhaps thousands of times their size.
Humans also have extraordinary brain capacity. This is somewhat due to our large size, but can also chiefly be attributed to the amount of breathable oxygen we have available to fuel our brains. In the ocean, marine creatures are restricted to oxygen dissolved in the water, ~500 times less abundant than the oxygen we have available in the air (volume wise). A species of human-sized fish would require a set of gills multiple times the size of their own body to inhale enough oxygen through ocean water to power an intelligent brain, which is obviously impractical. Mammals which surface to breathe air do exist in Earth’s oceans, like whales and dolphins. However it is important to note that these creatures’ ancestors actually evolved on land, and then moved back into the ocean. Given enough time, it might be possible for air-breathing creatures to evolve on an ocean world, but an alternative method of attaining oxygen could be bio-electrolysis. Water is composed of hydrogen and oxygen. If a species could develop a natural way to split water into these gaseous components using their own bodily energy, then perhaps it could use this oxygen to fuel its evolving brain, exhaling hydrogen gas as a byproduct. A human-mass ocean creature would have to consume 5 extra meals per day to garner enough energy to do this.
Finally, humans gained intelligence because we had an efficient mode of communication. Communication is vital to the development of intelligence to pass knowledge on to others of your species so that it can grow and learn. Though we largely communicate with verbal signals, an emerging intelligent species could develop any number of communicative methods using the senses we know. Underwater, sounds carry much farther and faster than they do on land, meaning that vocal communication may actually be even more efficient for a race of intelligent ocean life than it is for species of land life. On the contrary, light is greatly restricted in range underwater, making visual communication more difficult. It is possible that multiple forms of Earth dwelling marine life have already met these three criteria, but have the inability to take their intelligence to the next step…
Using Tools
Once an intelligent species had evolved underwater, it would desire to better itself and its kin by inventing things to make life easier. To achieve this, said species would require a form of opposable digits (or tentacles!) in order to manipulate the materials around it to use as tools. For humans, this trait enabled the building of shelters to protect from the elements, organized hunting and farming for easy access to food, and a mode of written communication to pass this knowledge on to the rest of our species.
It is pretty easy to see how an underwater species could develop shelters and farming, but the most crucial inhibitor towards an underwater species gaining intelligence may actually be written communication. On land, humans quickly learned that passing knowledge along via stone carvings was difficult because stones are heavy and take up a lot of volume. Using the pulp of ground up plants dried in the sun, humans developed papyrus; an ancient precursor to paper which was very lightweight and could be bound into a book for easy transportation. The advent of papyrus allowed our race to spread knowledge quickly between distant civilizations. An ocean species, however, would have no such medium. Any analog to paper would dissolve in water over short time frames, and would be impossible to write on with any sort of ink. An intelligent marine race may be able to develop written communication by etching into the compressed skins of other ocean life (i.e. leather), but even this will erode away faster than it would on land. Because of this, an ocean species may be restricted to stone carvings for thousands of years after attaining intelligence.
A landmark technology which humans developed that may not be as necessary underwater is the wheel. On land, strong gravity makes it difficult for bipeds to traverse long distances on feeble joints. By taming other land animals and constructing carriages with wheels, humans were mobilized to explore and traverse the Earth’s surface faster and more effectively. However, most ocean life evolves with a similar density to water, so no gravitational weight is imparted on them. Furthermore, wheeled vehicles would probably travel slower than most swimming underwater wildlife. The development of the wheel, then, would likely only be necessary for the construction of large stone underwater cities, and not as vital for transportation of goods and citizens. Instead, an underwater species may use nets harnessed to other domesticated ocean creatures to “drag” their goods efficiently from one location to another.
Finally, though the mastery of fire was pivotal for the evolution of our race, it (or anything like it) wouldn’t be necessary for the early evolution of an underwater species because ocean temperatures are not as drastically affected as air temperatures on short time scales. It may, however, inhibit their development into the metal era. Metals, though not entirely necessary, aided our species in building more durable, customizable parts for advanced tools and machines. Without a source of heat, metal ores could never be melted and purified underwater. One potential solution to this is underwater sea vents, some of which produce enough heat to melt rock. It may also be possible for an underwater species which has advanced enough to build land-based infrastructure underwater, and then raise it above sea level when ready for operation.
The Underwater Modern Age
For a developing intelligent underwater species, movement into the modern age may be a difficult hurdle to overcome. Such a species would first require a powerful and reliable energy source. Oil may be a viable solution, as oil deposits are abundant underwater. After harvesting the oil, an ocean species could either find ways to build underwater “combustion tanks” using a series of pumps and pipes to extract air from the surface, or just build their power plants from the seafloor, up to above sea level. Alternatively, an ocean species may actually develop fission power first, because no air is required to extract nuclear energy, and ocean water itself acts as a nuclear insulator. However it is generated, electricity from these plants would need to be well insulated when wired to consumers to prevent loss of energy or electric shocks through the water. Any personal electronic devices would also require strategic insulation. This insulation could come from bio-engineered plastics, produced from their oil and some sort of oil-consuming ocean life form.
An intelligent marine species would likely develop submarines for the efficient transportation of goods and citizens, but because of water’s high density compared to air, they would soon realize that this method is far too slow for the modern age. Instead, expressways of tubes filled with water and driven by pumps accelerating that water around city centers may turn out to be an ocean civilization’s analog to humanity’s freeway systems. In places where such infrastructure has yet to be built, water-filled boats and even aircraft may be devised to take advantage of the lower levels of drag induced by air. Eventually, it would become prudent for an ocean species to explore the land, perhaps in strange water-filled rovers.
After hundreds of years of advancing technology, an intelligent ocean dwelling species may look to the stars and wonder if extraterrestrial intelligent life could ever evolve elsewhere, maybe even on land. To answer this question, they may start their own space program. Crewed space missions would be greatly restricted due to the excess weight of transporting tons of water up for them to breathe, but nothing would prevent them from launching space probes from floating platforms into orbit, and around their home system. Regardless of how long it would take, there is no reason to suggest that intelligent marine life wouldn’t be just as curious about exploring the cosmos as humanity is.
Conclusion
The development of an intelligent marine species may take several billion years more than a land species like humanity to emerge. Sun-like stars may not burn long enough for such life to evolve, but red dwarf stars are abundant, and can live for hundreds of billions of years. This would provide ample time for an ocean world orbiting in such a star’s habitable zone to develop life, and allow it to become sentient. Planets like those in the Trappist-1 system, doused in radiation from their host star, may not be hospitable for land life to survive. However, beneath a dense layer of insulating ocean water, marine life may not be such a stretch.
It is safe to say that the evolution of an intelligent marine civilization can’t be ruled out. Though the development of ocean-based intelligence would face some substantial roadblocks, it would only be a matter of time before they would begin to discover the same truths that we know, and ask the same questions that we ask ourselves today. Just by looking at life on Earth, we can see that it evolves everywhere. It vies to become bigger, better, and more complex. It spreads like wildfire. If the same laws of evolution are upheld elsewhere in the galaxy, why would life confined to the depths of a planet-sized ocean be any different? All life needs water; and nothing is stopping that life from becoming intelligent within it.
