spaceSpace and Physics

What Would Aliens Look Like? The Answer May Surprise You


Jonathan O'Callaghan

Senior Staff Writer

From left to right: A simple replicating alien molecule, a simple cell-like entity, and an alien with intricate parts. University of Oxford

Science fiction normally depicts aliens in one of two ways. The first is that they look almost identical to us (hello Star Trek). The other is they are something wildly beyond our imagination, say, the heptapods in Arrival.

A new study published in the International Journal of Astrobiology, however, has a different idea. Taking a theoretical approach to astrobiology, the researchers from the University of Oxford say we can predict some Earth-like characteristics that aliens might have.


“We can’t say what aliens will look like in the sense of specific traits or adaptations, such as big green eyes or arms and legs,” Samuel Levin from the University of Oxford, the study’s lead author, told IFLScience. “Instead, we're arguing that aliens will be subject to the same rules of natural selection as we are, and as a result will have similar kinds of adaptations.”

Previous estimations on alien appearance have focused on what we can see here on Earth. For example, we think eye-like organs might evolve on other planets, because they’ve done so here at least 40 times and are found throughout the animal kingdom.

This paper, however, uses evolutionary theory to examine whether that holds true. They say aliens are likely to undergo similar biological processes, using multiple “units” – for us those are single cells – to work together for a common goal.

Even if they don’t have DNA like us, being maybe silicon-based or breathing nitrogen, they should still follow similar evolutionary paths. Along the way, they will pass through “bottlenecks” in evolution, just like we did.


On our planet, species complexity has increased thanks to events known as major transitions. These are when separate organisms evolve into a higher-level organism, such as cells forming multicellular organisms. And it looks like these rules kind of apply anywhere.

“In short, evolutionary theory does tell us that they will be subject to the same biological rules and have similar structures to life on Earth,” said Levin.

An alien with multiple parts working together, dubbed "The Octomite". University of Oxford

Now, this doesn’t mean that we can say aliens will have appendages or eyes like us. But we can say that complex alien life should build up in a similar way, with various parts working together.

“This could mean a collection of replicators, like the first genomes on the Earth, or some hideously complex nesting of groups on a planet where many more transitions have occurred than on our own,” the team write in their paper.


The idea is that single-celled organisms sometimes group together to form what are sort of working colonies, with each having a different role. Humans, for example, are made of cells, but none can live independently.

We don’t know if aliens will even be made up of cells, but the researchers argue they are likely to be made of parts, which are made of parts, and so on. Entities made up of smaller entities, to be exact.

So just like we started as single cells, so too are aliens likely to be built up by units. They are then likely to evolve in ways that reduce conflict between the parts – natural selection, in other words.

While there are invariably some things about alien life we cannot predict, there are some things we can. And that could help us work out what we might find out there, if anything.


“I think evolutionary theory offers a really important and under-utilized tool in the search for life beyond our planet,” said Levin.

As to what that means for science fiction, well, we probably can’t draw a picture of what aliens might look like just yet. But evolutionary theory could let us come up with some more imaginative ideas that still fit with our existing theories.

“Whether or not Ewoks or Na'vi exist, if they did, we can say a lot more than people might guess about their internal components, how their life cycles start, and what their evolutionary history is,” said Levin.


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