British scientists have claimed alien lifeforms may have evolved in a similar way to the organisms here on Earth.
A new study from the University of Oxford suggested that the process of natural selection which created the myriad species we see here on Earth is likely to have taken place on other planets too.
However, this does not mean aliens will resemble beautiful human beings.
Natural selection is a process outlined by Charles Darwin which suggests that the species which are best suited to their environment are most likely to survive to pass on their genes.
On Earth, this has led to the evolution of humans over billions of years.
But on another world, life is likely to look radically different depending on the conditions on the planet.
Sam Levin, a researcher at Oxford’s Department of Zoology, said: "We still can't say whether aliens will walk on two legs or have big green eyes. But we believe evolutionary theory offers a unique additional tool for trying to understand what aliens will be like, and we have shown some examples of the kinds of strong predictions we can make with it.
"There are potentially hundreds of thousands of habitable planets in our galaxy alone. 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 neighbors are like."
On this planet, events known as "major transitions" have driven the evolution of different species.
These events take place when one group of organisms evolve into "higher level" types of lfe.
This happened when single cell organisms evolved to become organisms made of several cells - or when the first societies of primates formed, eventually leading to the rise of humanity.
"By predicting that aliens have undergone major transitions - which is how complexity has arisen in species on earth, we can say that there is a level of predictability to evolution that would cause them to look like us," Levin added.
He suggested aliens would have evolved similar "mechanisms" to humans, allowing them to "eliminate conflict, maintain cooperation and keep the organism functioning".
He added: "In our paper, we offer an alternative approach, which is to use evolutionary theory to make predictions that are independent of Earth's details. 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."
A scientist who used to work for Nasa recently suggested that aliens could be living beneath the frozen oceans of sub-zero water worlds.
It's believed the vast majority of habitable planets in the universe are covered in seas and oceans, meaning that aliens could look more like fish than humans.
Levin's study was published in the International Journal of Astrobiology.
This story originally appeared in The Sun.