What would aliens look like? More similar to us than people realise, scientists suggest

Scientists might finally have worked out what aliens would look like. And it seems they would be shockingly familiar.

Alien life tends to be imagined as strange powerful monsters: either grey humanoids or insect-like killing machines. But they might actually look a lot more like us than we realised, according to pioneering new work by scientists looking to understand what extraterrestrials would actually look like.

The problem with imagining life on other worlds is that unfortunately we've only got one example to go by – our own. So we tend to imagine something that either looks like us or looks like something else on Earth, but there's no guarantee that would be accurate.

Instead, the new study applies evolutionary theory to understand what alien life might look like. And it finds that it would be subject to the same processes and mechanisms that helped bring us about – leading to the conclusion they might actually look a lot like us, too.

"A fundamental task for astrobiologists (those who study life in the cosmos) is thinking about what extraterrestrial life might be like," says Sam Levin, a researcher in Oxford’s department of zoology. "But making predictions about aliens is hard.

"We only have one example of life – life on Earth – to extrapolate from. Past approaches in the field of astrobiology have been largely mechanistic, taking what we see on Earth, and what we know about chemistry, geology, and physics to make predictions about aliens."

That's one reason why scientists are so excited about the possibility of finding life on other planets, for instance – like the suggestion that there is alien life in our own solar system on Saturn's moon Enceladus. Looking at another form of life would signal a profound way of understanding the very possibilities of how living things arise, and what life itself means.

"In our paper, we offer an alternative approach, which is to use evolutionary theory to make predictions that are independent of Earth's details," Levin says. "This is a useful approach, because theoretical predictions will apply to aliens that are silicon based, do not have DNA, and breathe nitrogen, for example."

By presuming that aliens are subject to the same kind of natural selection, the scientists can come to other conclusions. On Earth, complex species have arisen as a result of what are called major transitions – extreme events that force separate organisms to evolve into a higher, more complex organism.

The researchers note that they can't say exactly what alien life might look like – whether they have grey or green skin, big eyes or any other common look for alien life. But it does let them conclude that they could look potentially more like us than had been expected.

"Like humans, we predict that they are made-up of a hierarchy of entities, which all cooperate to produce an alien," says Levin. "At each level of the organism there will be mechanisms in place to eliminate conflict, maintain cooperation, and keep the organism functioning. We can even offer some examples of what these mechanisms will be."

Of course, we don't know whether there are even other forms of alien life out there in the universe – whether it ever existed, existed and then wiped itself out, or is ready and waiting somewhere nearby for us to find it.

"‘There are potentially hundreds of thousands of habitable planets in our galaxy alone," says Levin. "We can't say whether or not we're alone on Earth, but we have taken a small step forward in answering, if we're not alone, what our neighbours are like."