For a long time, many (mainly children, filmmakers and scientists) have wondered what aliens might be (if, of course, you imagine that they really are). Do they look like humans or take on a different form that a person cannot even imagine? The answer to this question really depends on our understanding of evolutionary processes taking place at the deepest level.
The merit of Hollywood cannot be overemphasized, which has provided the world with a whole collection of humanoid aliens. Initially, this "form of extraterrestrial life" was a necessity, since there were no special effects today, and the actors performed tricks in alien costumes. For example, let's remember the famous Alpha from the planet Melmak.
But even now, when special effects can be created by any unseen creature, the extraterrestrial race still takes on human features in order to better emphasize interaction with the inhabitants of the Earth. You can't do without mentioning the famous movie "Avatar".
At the same time, the only life forms that can really be studied are here on planet Earth. They all have the same ancestry and probably have a common ancestor. The latter, by the way, gave life to 20 million existing species of animals alone, and they are still trying to study its nature.
The types of structure of all these organisms can now be divided into 30 large groups. However, before the so-called Cambrian explosion, which occurred about 542 million years ago, an even greater variety of organisms could have been present on Earth. For example, there is known Opabinia - a genus of fossil animals, the remains of which were found in the deposits of the Cambrian period. This creature had as many as five eyes on the back of its head.
A bit of theory: In many areas of science, there is a method known as thought experiment. Running to him, Stephen Jay Gould speculated about what might happen if you rewind the "tape of life" back and then restart it again. In his opinion, the history of evolution would be completely different. Gould argued the importance of chance in evolution: the consequences of changing just one tiny thing are hard to imagine.
For example, after that very Cambrian explosion, the picaia creature survived, which subsequently gave birth to fish, amphibians, reptiles, mammals and, ultimately, humans. But what would happen if this organism died? Could another group have spawned intelligent beings? If so, then you could probably now read this article with five eyes instead of the usual two. For this reason, scientists ask the question: if the history of evolution is so fragile, then why should aliens evolve on other planets, at least remotely resemble us?
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According to evolutionary biologist Simon Conway Morris, the answer lies in evolutionary convergence, the process by which distantly related animals share similar traits. For example, the streamlined shape of dolphins, tuna and extinct ichthyosaurs, similar to each other, developed independently in each species: they all needed fast speed under water.
Other scientists are concerned with the issue of alternative biochemistry. Terrestrial life developed on the basis of carbon - this element forms stable chains and stable, but easily broken connections with other elements. Other elements (in particular, silicon, sulfur or boron) form less stable compounds under conditions of earthly temperatures, however, they can expand the concept of "life".
In addition, life is impossible without water or other solvent.
Continuous development, in turn, requires a mechanism for storing and replicating information with moderate accuracy, such as DNA, RNA (or their analogs).
It turns out that if the above conditions are met, life may well develop on other planets. It is not excluded that it, for example, is "stuck" at the stage of unicellular organisms, as it once was on Earth. After all, the first cells on our planet appeared quite early, but it took multicellular animals almost three billion years to evolve.
As for the structure of bodies, biologists here are repelled by terrestrial animals. The latter (with some exceptions) feed on primary producers or each other. Finding food requires a body structure so that the mouth is at the beginning of the body, which means that the animal needs to have a head and tail. The teeth, and probably the jaw, evolved to hold and grasp prey. In addition, movement on a hard surface requires a special structure at the contact boundary (cilia, muscular feet or legs), so there must be two sides - the back and the upper. This structure usually gives the body bilateral symmetry (left-right), which we see now: most animals belong to a special group called Bilateria - bilaterally symmetric.
However, despite all the many arguments in favor of a humanoid image of alien beings, no one knows if they will resemble humans. So, for example, many human organs are paired - because of our (perhaps just inevitable) bilateral symmetry. But all other parts of the human body are probably just a matter of chance. For example, the fact that we have five fingers and toes is a consequence of the reliance on the same fingers of our ancient ancestors. However, their own close relatives relied on seven and eight fingers.
According to experts, one of the tasks of evolutionary biology is to try to separate the functional and random development of organisms. This, in their opinion, will help us better understand how alien life can be different or similar to humans.
We also add that today the main method of searching for intelligent life in space is to listen and study radio or gamma broadcasts. Such methods focus more on star systems with Earth-like planets. According to scientists, it is in such worlds that life can exist.
Evgeniya Efimova