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.