Thoughts about what aliens look like seem to have haunted scientists and film producers for decades. If, nevertheless, aliens exist, then will they be similar to us, or will their forms go beyond our wildest fantasies? The answer to this question depends on how evolution works at its deepest level.
The film industry over the years has introduced audiences to mostly humanoid aliens from other worlds. Initially, this was out of necessity, since it was inconvenient to perform special effects while constantly being in a rubber suit. Oddly enough, now that with the help of computer programs it has become possible to create a wide variety of moving images, aliens have become more and more like people, which helps viewers create an emotional connection with them. An example is the movie "Avatar" by James Cameron.
Currently, the only life forms we can study are here on Earth. They originated about 3.5 billion years ago, and one common ancestor gave rise to the emergence of more than 20 million animal species with 30 different body types. In the Cambrian period (about 540 million years ago), the most favorable conditions for the emergence of an even greater variety of life forms were created on Earth. One has only to look at the arthropod opabinia with five eyes or dinomiscus - an animal in the form of a flower, together with a distant ancestor of man, chordate picaia.
In a famous thought experiment, biologist Stephen Jay Gould wondered, "What would happen if we could rewind the tape of 'life' and start it up again?" Gould mentioned the importance of randomness in evolution: if you change one little thing early on, it can lead to significant consequences over time.
In our version of history, we know that the chordate pikaya survived and eventually became the ancestor of fish, amphibians, reptiles, mammals, and humans. But what would happen if she died? Then other species would lead to the emergence of intelligent beings, and, quite possibly, people would look at the world with five eyes, and not two.
If the origin of intelligent beings on Earth was literally hanging by a hair's breadth, then why could aliens evolving on a wide variety of planets be like humans?
The answer to this question, according to evolutionary biologist Simon Conway Morris, lies in the phenomenon of evolutionary convergence - a process in which even distantly related animals are very similar to each other. For example, dolphins, tunas, and extinct ichthyosaurs that evolve independently of each other have the same streamlined shape to move efficiently through water at high speed.
What are the aspects of alien biology? First of all, it is carbonaceous biochemistry, since carbon, creating form-stable main chains of macromolecules, forms stable, but easily destroyed bonds with other elements. Other elements, such as silicon and sulfur, form less strong bonds at temperatures like on Earth. Water or some other solvent is also required.
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Evolution requires a mechanism for storing and reproducing information with moderate fidelity, such as DNA, RNA, or a similar analogue. Although the first cells on Earth appeared quite early, it took almost 3 billion years for the development of multicellular animals … So it is quite possible that life on other planets could get stuck at the unicellular stage.
On a planet similar to Earth, it is also likely that radiation from a native star or multiple stars will be used as an energy source. Large multicellular organisms can efficiently use light energy using leaves and branches. Such forms in the form of plants have developed widely on Earth.
With rare exceptions, animals feed on smaller creatures or eat from each other, and there are only a few ways to do this. First, you need a mouth to eat, so animals must have a head. And then the jaws and teeth develop to grab food. To move on a hard surface, special formations are needed, for example, cilia, muscular legs, preferably front and back. And as a rule, stability requires bilateral symmetry, which most living things have.
What about big brains and intelligent creatures that can travel interstellar distances? On Earth, relatively large brains and the ability to use tools have evolved in monkeys, whales, dolphins, dogs, parrots, crows, and octopuses. However, the monkeys have mastered the use of tools to a much greater extent. As a result, they began to walk on two legs, freeing their front limbs, and also acquired dexterity in the fingers, which became the key to the origins of writing. Humans have two eyes and ears, just enough for stereo vision and hearing, and paired limbs. There are also many paired organs, which is inevitable due to bilateral symmetry.
However, other parts of the human body may be nothing more than an accident. The fact that we have arms and legs with five fingers is a consequence of the fixation on five of our early four-legged ancestors, and in the earlier period they had six, seven and even eight fingers.
Ultimately, the jury can make its conclusion - intelligent life forms, if they exist, are like us. And understanding the causes of the emergence of functional and random elements helps to understand how aliens can differ from us.
The search for intelligent life in space is mainly done by listening to radio or gamma broadcasts. These efforts are most often focused on stellar systems with exoplanets. After all, it's easier to look for “life as we know it” than something inexplicable.
Voronina Svetlana
