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When we try to picture what an alien living on Kepler-452b might look like, the first image that comes to our mind is that of a greenish creature with shiny big eyes and a giant brain. However, this impression is about to change as a new scientific study from the University of Oxford has shown that aliens might in fact be more similar to us than we think.

It is estimated that our galaxy, the milky way, contains around 100 billion planets. Moreover, scientists have calculated that about 22 percent of all sun-like stars in our galaxy have Earth-sized planets that orbit them in the habitable zone. Even If we assume that only 0.001 percent of those sun-like stars have planets that are home to some form of life, that would still leave us with 400,000 life-supporting exoplanets. Given that huge number, a study published in the International Journal of Astrobiology, suggests that aliens in other planets would have likely undergone natural selection, resulting in a multitude of potential species that are shaped by the same mechanisms that shaped humans. However, this doesn't necessary mean that those aliens will look exactly like us. It simply indicates that this potential form of life would odds-on have resulted from natural selection.

In 1859, Darwin showed that all the biodiversity we witness around us can be explained by a simple mechanism, which he aptly dubbed "natural selection". In a nutshell, organisms that have traits that give them a survival advantage are more likely to have offspring than those who don't have those traits. By reproducing, they pass on these traits to the next generation. Over time, the whole population of these organisms will only contain those that have the beneficial traits. Through the culmination of small improvements, natural selection ultimately results in creatures that appear as though they were specifically designed for their environment. For instance, we have previously talked about jumping spiders who imitate ants to avoid predators. This illusion of design is merely the result of small incremental adaptations that occur over a very long period of time (i.e., millions of years).

By arguing that the only way to get an organism that appears to have a so-called sense of purpose which manifests itself in their ability to self-replicate is through Darwin's theory, the scientists have determined that aliens will likely undergo natural selection. While natural selection can precisely explain the mechanisms behind the apparent design we would see in aliens, it doesn't tell us anything about the emergence of complex organisms. The complexity of life on Earth resulted from a series of conditions called major transitions. Basically, a transition occurs when a group of structures cooperate to form a higher level organism. For example, the shift from single-celled organisms to multicellular life forms is a major transition.

Like on Earth, the researchers also predict that alien complex life likely arose as a consequence of major transitions. So what does all this jargon mean in layman's terms? Essentially, the fact that alien life is shaped by natural selection and major transitions simply indicates that humans and aliens are governed by the same biological mechanisms and laws. However, there is nothing that prevents alien species from looking different than their earthly counterparts.
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