Children, filmmakers and scientists discussed what might be aliens on view for decades. If they did exist, what would they be? Similar to us? Or like our worst nightmares? The answer to this question depends on how evolution works at the deepest level. Hollywood, for years, regaled us with images of extraterrestrial races, and most of them were humanoid. Initially this was necessary because the special effects required that someone climbed in a rubber suit. Now, when everything is done using computer graphics (CGI), the aliens are similar to humans only in cases when you need to establish with them an emotional connection, to feel them — as in “Avatar” by James Cameron.
Currently, the only forms of life that we can study, live on the Earth. 3.5 billion years ago, they had one origin, and that common ancestor gave rise to at least 20 million living species. They all have a body, organized in accordance with about 30 different body plans in the major groups called Phil.
But when about 542 million years ago animals first diversified during the Cambrian “explosion” could be an even greater variety of basic body plans. Take a look at Patillas armored Opabina on the image above or stalked and almost floral Dinomichus next to our own distant relative, chordates Pikaia.
Restart film life
In the famous thought experiment of the biologists Stephen Jay Gould asks the question: what would happen if we had the opportunity to rewind the “tape of life” and run it again? Gould insisted on the importance of chance in evolution: change one little thing at a very early stage and eventually the consequences will emerge all the stronger. In the version of history that we know Pikaia or something similar to it survived and eventually led to the emergence of fish, amphibians, reptiles, mammals and the number of beds in the expense of ourselves. But what would happen if she died? Could another group lead to the emergence of intelligent beings, for example, with five eyes? And you would now be blinking alternately, then two, then three? If our own origins on Earth really depended on such delicate eyelets of chance, why, then aliens can live on other planets — should be anything like us?
The answer to this question, according to evolutionary biologist Simon Conway Morris, lies in the phenomenon of evolutionary convergence: the process by which distantly related animals are quite similar to each other. For example, the similar streamlined shape of dolphins, tuna and the extinct ichthyosaurs evolved independently in response to the same selective leverage: it was the task as efficiently as possible and move faster in the water.
But what you would expect from the alien biology? Biochemistry based on carbon is the most probable, given the fact that carbon forms a stable (but quite destroying) relationships with other elements and long connections. Other elements, particularly silicon and sulfur, and form less stable relationships when the earth’s temperatures. Water or other solvent, too, seems quite necessary. That evolution took place, requires a mechanism for the storage and reproduction of information with reasonable accuracy as DNA, RNA or other equivalent. Although the first cells appeared on Earth quite early, and multicellular life took 3 billion years to develop. It’s possible that life on other planets also stuck in the unicellular stage.
On the planets of earth type are also likely to expect that the radiation of the sun (or suns) will be used as a source of energy for biochemical reactions. For moderately large multicellular primary producers, effective use of light will require a collection system in the form of leaves and branches. Similar shape and behavior evolved, converged on Earth, so one would expect “plants” with the very familiar forms on other planets of the earth type.
With rare exceptions, the animals either eat the primary producers, or each other, and ways to make it not so much. The absorption of food requires a moving mouth, so the animal will head. Teeth and jaw will probably appear to help hold and chewing of food. Moving on a hard surface will require specialized structures (e.g., cilia or muscular foot), thus the front and rear. It will also give bilateral (left/right) symmetry: indeed, most of the animals belong to the Bilateria supergroup.
But what about giant intelligent insects?
Well, what we’re all about people but about people. Insects represent the most species-rich group on Earth, why the aliens are not to be like them? Unfortunately, when you have external skeleton, it is very difficult to grow: it is necessary to periodically molt, reset the scales and it all to grow. On planets like Earth, any relatively large terrestrial animals with external skeletons will just bend under its own weight during molting. And complex brains require a certain size.
On Earth, relatively large brains are correlated with the use of guns to some degree and the ability to solve problems and appeared many times: monkeys, dolphins, whales, dogs, parrots, crows and octopuses. However, the apes have developed the use of tools to a much greater extent. This is partly due to walking on two legs, which frees the forelimbs, as well as with the dexterity of our fingers (which can also be a clue to the origins of writing).
In the end, the jury biologists agree that intelligent aliens — if they exist — will be similar to us. Can be in varying degrees, it is important that people have only two eyes and two ears (what you need for stereo and hearing) and only two legs instead of four, for example). Other organs are also arranged in pairs, as a consequence of our evolutionary deep-seated — and perhaps inevitable — bilateral symmetry. However, other elements of our body plan are nothing more than a coincidence. The fact that in the hands we have five fingers, is a consequence of fixing fingers of our early ancestors among tetrapod — close relatives experimented with seven or eight.
In fact, the majority of species were subject to random “locks” during the development — over time, the body plans became stereotyped and lost flexibility. The separation of functional from random is one of the greatest challenges in evolutionary biology can help us better understand how alien life forms may be different from us.
The basic process of our search for intelligent life in outer space is to listen to the radio or gamma-ray transmission. Most often, these efforts focus on star systems with planets like the earth, because they, we believe, likely to Harbor life. In the end, it’s easier to look for the life we know than the one you don’t know.
