Aliens by Darwin

    In our galaxy alone, there are approximately 100 billion planets. About 20% of them are likely to be in the habitable zone, which allows the existence of the biosphere. Even if life was born on only 0.001% of these planets, in our galaxy there are about 200,000 inhabited planets. At the same time, the radio signal of the technogenic civilization of the Earth has already spread within a radius of 70 light years - and continues to spread, informing everyone about our existence. Given the highest chance of meeting an alien life form, it is not surprising how rapidly astrobiology is developing. In the search for extraterrestrial life forms in the United States and Europe, hundreds of millions of dollars are invested . Almost any branch of science can envy such investments.

    Many scientific articles have been published with attempts to analyze how aliens might look: for example, see the works of Benner (2003) , Devays (2009) , Rothschild (2009) , Rothschild (2010) , Shostak (2015) . For example, Shostak from the SETI project expresses the opinion that we are more likely to meet with some kind of artificial life form (maybe robots under the control of AI).

    In any case, it is interesting to know what the biological form that created this AI looks like.

    Until now, attempts have been purely mechanical to predict this - by extrapolating the experience of terrestrial evolution (unfortunately, we are still familiar with the experience of evolution on only one planet, so it is difficult to do other extrapolations). For example, it is known that during evolution, the ocular organs (photoreceptors and eyes) evolved at least 40 times(or up to 65) and are present in 95% of terrestrial animals. So something similar should be with aliens. Other mechanical extrapolations about the chemistry and physics of aliens are made in the same way. For example, carbon is found in abundance in the Universe, exists in various forms, forms diverse chemical compounds and is in interstellar matter - it is logical to assume that alien life should be based on carbon. But all this is pure extrapolation. There is no theoretical reason why extraterrestrials cannot be a silicon eyeless life form.

    Another option for predicting the appearance of extraterrestrial life forms is to use theory. In this case, it is a theory of evolution. At least, it was this theory that made it possible to predict and describe the many biological effects on Earth: from animal behavior to their morphology. For example, why do some organisms, especially insects, need to change the sex of their offspring or why men in humans should be larger than women. Evolutionary theory really works in practice and is capable of predicting and describing real effects. So why not apply this (universal) theory in an attempt to describe the possible appearance of aliens? A team of scientists from the Department of Zoology at the University of Oxford is Samuel R. Levin, Thomas W. Scott, Helen S. Cooper, and Stuart A. West) - for the first time in the history of science, they tried to combine mechanical and theoretical approaches to solve this problem, that is, to describe the appearance of aliens. Their scientific article, “Aliens by Darwin” (“Darwin's aliens”)published on November 1, 2017 in the International Journal of Astrobiology (doi: 10.1017 / S1473550417000362).

    In their work, they discuss some aspects of the theory of evolution. For example, should there be a natural selection for aliens and what consequences will it lead to if it exists.

    Then they examine the specific possible type of alien organism: complex multicellular organisms. How such organisms appeared during the Earth evolution, how they can arise in another part of the Universe, and what biological properties can be expected from aliens.

    Darwin explained that natural selection works thanks to three functions:

    • diversity (creatures differ in behavior and structure);
    • reproductive success (some signs of behavior or the body increase the likelihood of leaving more offspring than relatives).
    • inheritance (creatures transmit their characters to offspring);

    These three functions are shown schematically in the figure.

    Illustration: University of Oxford.

    Successful traits gradually accumulate in a population, and evolution happens. Other characteristics may become beneficial due to changes in natural or other conditions, so evolution does not stop.

    That is, the existence of natural selection requires the presence of all three of the above functions: diversity, reproductive success and heritability. If they are, there is a natural selection, regardless of the genetic system of the body or the type of planet.

    Natural selection explains not only the reason for evolution, but also the reason for adaptation. Even earthly nature shows that during evolution, organisms are able to adapt to life in the most incredible conditions. If you give the body enough time, then in the end it will become as if it were specially designed for life in these conditions. This is a kind of "design without a designer", everything happens in a natural way.

    Random mutations can also drive the evolutionary process, but without natural selection they are practically meaningless. It is very unlikely that complex organs like the lung or the eyes may appear as a result of random mutations. Here, natural selection plays the role of a guiding forcewhen only the desired mutations are selected, as if the design of the desired organism is created in advance, which will be most adapted specifically to these conditions.

    So, will natural selection act on other planets in outer space, scientists from the University of Oxford ask. And they immediately answer: yes. The theory of evolution says that it cannot be otherwise, except for the simplest molecules. Without a designer, the only way to get an organism adapted to the conditions, which is aimed at maximum reproduction, is natural selection.

    Levin and colleagues urge not to be distracted by the definition of life and the specific functional differences between “living” and “nonliving” (replication, metabolism), because without natural selection the body will not be able to adapt to environmental conditions. Therefore, we simply will not find such an alien life form.

    For example, the illustration below shows three options for alien life. The first option is a simple molecule. Even if we consider this form of life, then it is so simple that it cannot pass through natural selection. The second option is also a very simple creature in the form of a cell. But it will already be able to adapt to environmental conditions. Finally, on the right is a creature with a large number of intricate organs working together. This gives the greatest adaptability. Such a creature could undergo the most significant changes in the course of natural selection, that is, it adapted longer than others to a change in external conditions.

    Three options for alien life. Illustration: University of Oxford.

    Here we come to the concept of complexity.. Scientists put forward the argument that it is such a complex creature that should be more than simple adapted to external conditions and their changes - this simply follows from the theory of evolution. It has evolved the longest - hence the conclusion.

    It turns out, it can be logically assumed that the most fit aliens that we can meet will be complex creatures with a large number of different organs. But this is not necessary because natural selection does not necessarily imply an increase in complexity for adaptation. However, we can say for sure that they will be more interesting for us.

    The authors of the scientific work pay attention to the question of how complexity arises. That is, how simple organisms become more complex. The answer is basic transitions(major transitions).

    The main transitions in evolution have several properties:

    1. Small objects can come together and form a larger object (chromosomes, eukaryotes, multicellular colonies).
    2. Smaller objects often stand out and exist inside larger objects (DNA and proteins, organelles).
    3. Smaller objects lose their ability to reproduce in the absence of a larger object (DNA, chromosomes, organelles).
    4. Smaller objects can disrupt the functionality of a larger object (parthenogenesis, cancer).
    5. New types of information transfer appear (DNA proteins, heredity of cells).

    The main transitions are very important in evolution, because thanks to them, organisms of greater complexity arise during natural selection. Life on Earth has gone through many such basic transitions, as shown in the illustration.

    The main transitions in the evolution of life on Earth. Illustration: University of Oxford.

    What will aliens look like who, through natural selection, have increased their complexity through many basic transitions? Several signs that they will possess can be predicted.

    An example of a complex alien creature that has gone through many basic transitions. Illustration: Oxford University

    1. The presence of larger entities created from smaller entities with a nested hierarchy. The complexity of the hierarchy and the number of investment levels depends on the number of main transitions. For example, in advanced cases, we can assume a “society of societies”, where many social colonies cooperate with each other, and each of them specializes in its function.

    2. Regardless of the number of transitions, there should be something that unites interests or eliminates conflicts between entities at the level of each transition.

    3. According to theory, there should be something to limit population growth - the easiest and best way to eliminate conflicts between entities.

    How are conflicts resolved?

    It may be something like a common mating partner for all, as witheusocialities - the highest level of social organization of animals on Earth. This is possible when combining similar entities. Having a common pair for mating unites the interests of all members. Or something like a single cell bottleneck restriction in multicellular organisms.

    Another option, if different entities are combined. For example, both mitochondria and the nucleus carry out joint reproduction. If heterogeneous individual entities are united together, then their interests are also united.

    In the end, conflicts of interests of entities can be resolved using both of the above options, as in humans.

    So, in accordance with the theory of evolution, aliens must undergo natural selection. These can be complex creatures that went through a series of basic transitions and developed appropriate mechanisms for resolving conflicts between entities that arise during the main transitions. Therefore, they must have a complex hierarchy of entities. Well, when everything is clear, it remains only to find them.

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