An alternate universe known as science fiction has given our culture a menagerie of alien species. From teddy bears like Ewoks to gruesome creatures like Aliens, our collective imaginations obligingly slap us into completely Hollywood imagery when we think of alien life. Whom to believe? What will the aliens be like when they appear on our radars - something completely different or strange versions of horror films from second-rate films?
One thing is certain: aliens from other worlds will obey the same evolutionary forces as we do on Earth - natural selection. This conclusion was reached by scientists from the University of Oxford, submitting their article for publication in the International Journal of Astrobiology.
Scientists speculate that the evolutionary theory presented by Charles Darwin in his famous book On the Origin of Species 158 years ago can be used to predict alien species. In particular, as scientists write, aliens will go through natural selection, because this is the only process by which organisms can adapt to their environment.
"Adaptation is what defines life," says lead author Samuel Levin.
While it's likely that NASA, or some sort of private enterprise similar to SpaceX, will eventually stumble upon space rocks and discover microbial life in the not too distant future, the aliens Levin and his colleagues are trying to describe are much more difficult. Because natural selection works.
Let's brush up on this a bit: natural selection is the process by which certain traits in a given population become preferred. For example, take a group of brown and green beetles. As birds prefer to feed on green beetles, more brown beetles survive and reproduce. If this population pressure persists, brown beetles will become the dominant species. Brown will win, green will lose.
And just as humans are the result of millions of years of adaptation - their eyes and thumbs, for example - aliens will be made up of parts that were once free-living, but have come together over time to work as one organism.
“Life has too many tricky parts, too many complexities, for this to happen (by accident),” explains Levin. “It's too hard and too many things have to work together and purposefully for this to happen by accident. We need a process of creation, and this process is natural selection."
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Just don't think the aliens are going to be bipedal humanoids with large heads and almond-shaped eyes, Levin says.
“They can be created from completely different chemical things and are visually unrecognizable,” he explains. “They will go through the same evolutionary history as we do. As for me, this is much more interesting and delightful than the fact that they will have two legs."
Lack of data
Seth Shostak, lead astronomer at the SETI Institute and presenter of the radio show Big Picture Science, believes that while the argument itself is interesting, it does not answer the question of alien appearance.
Shostak argues that convergent evolution would be a more productive approach, when similar adaptations take place in similar environments, at least if we assume terrestrial conditions like liquid oceans and thick atmospheres. For example, alien species that develop in a liquid environment are likely to have an elongated body that helps move through water.
"The randomness and specificity of the environment will lead to changes on an alien planet just like we do, and there is no way to predict them," concludes Shostak. “Alas, an accurate cosmic bestiary cannot be described by simply turning on biological mechanisms. We need data. Thinking about extraterrestrial life is not enough. We need to open it."
Search goes
The search is underway. On the one hand, the task seems simple enough: there are about 100 billion planets in the Milky Way galaxy, and about 20% of them can produce the biosphere. Even if the evolution of life is an extremely rare process, then even according to conservative estimates of 0.001% (200,000 planets), the chances will be quite high.
Of course, it is not so easy to place them on a segment of a billion light years.
Planet hunters can't even agree on what life signatures to look for. It is believed that there is no smoke without fire. If the alien world is home to biological life, astrobiologists will look for the presence of "biosignature gases" produced only by extraterrestrial life.
Scientists look for such gases by studying the planet's atmosphere against the background of starlight. Gases in the atmosphere absorb certain frequencies of starlight, suggesting what is happening in the cauldron of a particular planet.
The presence of oxygen, apparently, should be a biological beacon, but there are times when the planet can produce false positive results: that is, non-biological processes will be responsible for the appearance of oxygen on the planet. Scientists like Sarah Seeger, an astrophysicist at the Massachusetts Institute of Technology, argue that there are many examples of other types of gases produced by organisms even on Earth that could indicate life on another planet.
Life as it is
The existence of Earth-related extremophiles - organisms that can exist in the most incredible conditions, such as the vacuum of space - provides another clue as to what kind of aliens we might eventually meet.
Lynn Rothschild, astrobiologist and synthetic biologist at the Ames Research Center in Silicon Valley, takes extremophiles as a basis and perfects them using synthetic biology.
For example, let's say bacteria can survive at temperatures of 120 degrees Celsius. The Rothschild Laboratory can bring this threshold up to 150 degrees. The idea is to bring life to the point where it doesn't even need rockets.
While scientists cannot agree on where, how, and what we find in our search for extraterrestrial life, most of them are convinced that alien life must exist.
"I would be surprised if aliens didn't exist," Levin says. “Few things would shock me more than the conclusion that aliens do not exist. If I could bet, I would bet everything on the fact that extraterrestrial life is out there somewhere, and there is a lot of it."
Ilya Khel