The theory of biological evolution: what it is and what it explains

Man is a curious being who throughout history has questioned everything around him and proposed the most diverse ideas to explain it.

No wonder our ancestors also wondered about the animals and plants they saw around them: have they always been like this or have they changed over time? What if there were any differences, What mechanisms were used to make these changes?

These are the main unknowns that have been attempted to solve through what we know today as a theory of biological evolution, which is the basis of biology and communicates with much of the field of psychology, in the trends that could influence our behavior and our way of thinking. Let’s see what it is.

    Evolution of a fundamental theory in biology

    The theory of biological evolution is a set of scientifically developed explanations of how the fact known as biological evolution works. In other words, biological evolution is a process observed in reality (even in experimental contexts), and the theory of evolution is a set of “mounted” approaches to understanding this natural phenomenon.

    It should be remembered that a scientific theory is the most valuable status that a system of scientific laws and interconnected hypotheses can adopt when they have been successfully tested repeatedly and what they help to understand is not. can be expressed mathematically. This means, among other things, that if the theory of evolution is “only” a theory, to refute it, another alternative theory would have to be created; today, this hypothetical second theory does not exist, which is why it is the basis of current biology and biomedical sciences in general.

    On the other hand, the theory of evolution as we understand it today cannot be detached from the research and discoveries of Charles Darwin, without being limited to it. Today, the scientific community goes beyond Darwin’s propositions, although based on them and without denying their fundamental elements., And by combining this knowledge with that of the world of genetics as a field of research. But to better understand what this theory looks like, let’s start from the beginning: its beginnings and its precedents.

    Until the 19th century, the predominant idea about the origin of species was creationism. According to this doctrine, an almighty being had created each of the existing living beings, and these had not changed over time. This class of beliefs dates back to ancient Greece, and although they never became hegemonic in Europe, they have left their mark on the thinking of some theorists and intellectuals.

    But with the Enlightenment, more complex theories close to reality began to emerge in Europe. The most remarkable at the beginning of the 19th century is the proposal by Jean-Baptiste Lamarck; this French naturalist proposed that all species have the will to change and the ability to transfer these changes acquired through their actions to their offspring, a mechanism of transmission of characteristics called inheritance of acquired characteristics.

    Of course, it should be noted that Lamarck’s ideas were not based on the inheritance of traits present in ancestors and that they had developed from their interaction with the world; it was more concrete than that. According to this theory, the acquired characteristics are specifically those that result from proactive actions: for example, trying to switch from a diet based on rodents to a diet based on fish.

    Lamarck, in opposition to creationists, defended the idea of ​​the evolution of species, but admitted that species were generated spontaneously and did not have a common origin. In other words, his theory was only about the mechanism by which living things change over time, not how they first appear. I will not go into details, because you have here a very complete article on Lamarckism: “The theory of Lamarck and the evolution of species”.

    Charles Darwin and the theory of biological evolution

    A big step had been taken in admitting the idea of ​​biological evolution by entirely natural mechanisms, but Lamarck’s theory had many cracks. It was not until 1895 that the British naturalist Charles Darwin publish the book The Origin of Species, in which propose a new theory of evolution (which would be known as Darwinism). Gradually, this theory would take shape in his successive writings, and would be perceived as explaining biological evolution by a natural mechanism: natural selection combined with sexual selection. Then we will see what they consist of.

    Along with the British naturalist also Alfred Russel Wallace (who curiously conducted similar research and came to almost identical conclusions without having encountered a word with him), Darwin presented new ideas in favor of evolution; that yes, with great caution, because the implications of their work put in a delicate situation the succession of the Church, which had always attributed to the direct intervention of God the existence of all forms of life.

    Natural selection

    According to Darwin, all species come from a common origin, from which it has diversified thanks, in part to natural selection. This evolutionary mechanism can be summed up as the species best suited to the environment in which they are found, breed more successfully, and have offspring which, in turn, are more likely to breed successfully, leaving make way for new generations. The English naturalist also accepted the idea of ​​extinction, which was the other side of the coin: species less adapted to the environment tended to reproduce less and less, disappearing in many cases.

    So, in the first place, populations of living things with different characteristics appeared on the scene, and the environment put pressure on them that made some of them more reproductive than others, causing the spread of their characteristics and the disappearance of others.

    What characterized this process was its natural character, foreign to the influence of a supernatural entity. to direct it; this happened automatically, in the same way that a snowball grows under the influence of the force of gravity applied on the slope of a mountain.

    Sexual selection

    Another of the evolutionary mechanisms described by Darwin’s theory of evolution is sexual selection, which consists of a set of natural dispositions and behaviors that make some individuals considered more desirable to have offspring with, and others less desirable for them.

    like that, sex selection performs double play. On the one hand, it is supplemented by natural selection, because it provides elements that explain why some individuals have better reproductive success than others; but on the other hand it plays against it, because there are traits which can be advantageous from the point of view of sexual selection, but disadvantageous from the point of view of sexual selection (i.e. the outcome interaction with the environment, with the exception of possible breeding pairs).

    An example of the latter is the long peacock tail: it makes it easier to find a mate, but more difficult to stay out of reach of predators.


    Although removing divinity in creation and explaining a basic mechanism by which species change and diversify over time, Darwin was unaware of the term we know today as genetic variability, and nor did he know of the existence of genes. In other words, he did not know how the variability of the characters on which the pressure of natural selection acts. For this reason, he never rejected above all the idea of ​​the inheritance of acquired characters proposed by Lamarck.

    Unlike Darwin, Wallace never accepted this idea, and out of this dispute a new evolutionary theory called neodarwinism emerged., Prompted by naturalist George John Romanes, who, in addition to rejecting Lamarckian ideas in their entirety, believed that the only evolutionary mechanism was natural selection, which Darwin never discussed. It was not until the beginning of the 20th century that Mendel’s laws, showing that DNA mutations are pre-adaptive, that is to say that we first undergo a mutation and then test whether the individual to whom it was given is better suited to the environment or not, breaking the idea of ​​inheritance of acquired characters.

    With this premise, geneticists Fisher, Haldane and Wright gave Darwinism a new twist. They integrated the theory of the evolution of species through natural selection and genetic inheritance proposed by Gregor Mendel, all on a mathematical basis. And this is the birth of the theory currently most accepted by the scientific community, known as the synthetic theory. this one proposes that evolution is a more or less gradual and continuous change explained by genetic variability and natural selection.

    The social impact of the theory of evolution

    Darwin’s biggest problem was to dispense with the figure of the hand of God in his theory of what might be the explanatory mechanism of biological diversity, which is unforgivable in an age when religion and creationism were hegemonic.

    however, Charles Darwin’s theoretical legacy was strong, and over the years the emergence of new fossils gave good empirical support to his theory.… which did not make his contribution to science good on the part of religious organizations. Even today, environments closely tied to tradition and religion deny the theory of evolution, or view it as “just a theory,” implying that creationism enjoys the same scientific endorsements. Which is a mistake.

    Evolution is a fact

    Although we speak like the theory of evolution, it is in fact a fact, and there is evidence not to doubt its existence. What is discussed is how scientific theory should be to explain the evolution of species for which there is evidence, this process itself is not questioned.

    Below is some of the evidence that proves the existence of biological evolution.

    1. Save the fossils

    Paleontology, the discipline that studies fossils, has shown that geological phenomena take a long time to complete, such as fossilization. Many fossils are very different from today’s species, but at the same time, they bear a certain resemblance. It sounds strange, but with an example it will be easier to understand.

    The Glyptodon was a Pleistocene mammal that bears a striking resemblance to a modern armadillo but in a giant version: it is a trace of the evolutionary tree that leads to modern armadillos. The fossils themselves are also evidence of extinction, as they show that in the past there were organisms that today are no longer with us. The most emblematic example is that of the dinosaurs.

    2. Remains and imperfect designs

    Some living things have designs that we could say are imperfect. For example, penguins and ostriches have hollow wings and bones, but cannot fly. The same goes for the whale and the snake, which have a pelvis and a femur, but do not walk. These organs are known as vestiges, organs that were useful to an ancestor but are no longer useful..

    This is further evidence of evolution, which also reveals that this process is opportunistic, as it takes advantage of what it has to organize a new instance. Living species are not the result of smart, well-planned design, but are based on functional “clichés” that are perfected (or not) over generations.

    3.homologies and analogies

    When comparing the anatomy between different organisms, we can meet cases which, once again, are a test of evolution. Some of them consist of homologies, in which two or more species have a similar structure in some parts of their anatomy, but must perform different functions, which is because they come from the same predecessor. Examples are the limbs of tetrapods, as they all have a similar structural arrangement although their limbs have different functions (walking, flying, swimming, jumping, etc.).

    The other case is that of analogies, organs of different species which do not have the same anatomy but which share the function. A clear example are the wings of birds, those of insects and those of flying mammals. They have been developed by different paths to achieve the same function, that of flying.

    4. DNA sequencing

    Finally, the genetic code, with a few exceptions, is universal, which means that every organism uses the same thing. Otherwise, it would not be possible for the E. coli bacteria to produce human insulin by introducing the gene (of human origin) responsible for the generation of this substance, as we do today. In addition, GMOs are further proof that the genetic material of all life forms is of the same nature. Another proof that all species have a common origin and proof of evolution.

    evolutionary mechanisms

    Although we have spoken of natural selection as a mechanism that uses evolution to move forward, it is not the only one known. here we will see the different types of selection that influence evolution.

    1. Natural and sexual selection

    In the theory of biological evolution born in Darwin, this naturalist originated the idea of ​​natural selection from his observations on the voyage of the Beagle during its voyage through the Galapagos Islands. In them it was struck that each island had its own kind of finch, but they all bore a resemblance to each other and to those of the neighboring continent, South America.

    The conclusion he came to was that the island finches originally came from the mainland and on reaching each island they experienced “adaptive radiation”, in this case through food, thus generating a range of variants to from the same group of ancestors; for that, these birds have very different peaks from each other, having adapted to each island’s ecosystem separately.

    Today we can better clarify how natural selection works. The environment is not stable and changes over time. Species undergo random mutations in their genome, which causes them to change their characteristics. This change can help them survive or, in turn, make life difficult for them and cause them to die easily.

    2. Artificial selection

    It is not properly an evolutionary mechanism, but a variety of natural selection. It is said to be artificial because it is the human being who directs evolution for his own interests. We are talking about a practice that has taken place in agriculture and animal husbandry for millennia of choosing and crossing plants and animals for greater productivity and yield. This also applies to pets, such as dogs, for which other characteristics have been sought, such as more strength or more beauty.

    3. Genetic drift

    Before talking about this mechanism, it is necessary to know the concept of lel. An allele includes all mutational forms of a particular gene. To give an example, the different genes for eye color in humans. Genetic drift is defined as a random change in the allelic frequency from one generation to the next, that is, the environment does not act. This effect is best seen when the population is small, as in the case of inbreeding., Where genetic variability is reduced.

    This mechanism can remove or define features at random, without the environment having to act on its selection. And that is why in small towns it is easier to lose or acquire quality at random.

      Controversy linked to evolution

      As we have seen, the most widely accepted theory of evolution today is the Synthetic Theory (also known as Modern Synthesis), although there are alternatives that oppose this. it is considered to contain certain gaps or concepts which are not explained or not included.

      1. Neutralism

      Until recently, it was believed that only harmful mutations (negative selection) and beneficial mutations (positive selection) existed. But Japanese biologist Motoo Kimura said that at the molecular level there are many neutral mutations, which are not subject to any selection, and the dynamics depend on the rate of mutation and the genetic drift that eliminates them, creating a balance.

      From this idea was born an idea opposed to that proposed by the synthetic theory, where beneficial mutations are common. This idea is neutralism. This branch proposes that neutral mutations are common and that beneficial mutations are in the minority.

      2. Neolamarckism

      Neolamarckism is the part of the scientific community that still maintains that Lamarck’s theory and its inheritance of acquired characters cannot be excluded. From there, we try to reconcile this idea with genetics, claiming that mutations are not random but are the result of the species’ “effort” to adapt to the environment. however, its empirical basis cannot be compared to that of the synthetic theory.

      Bibliographical references:

      • Cracraft, J .; Donoghue, MJ (2004). Assembling the tree of life. Oxford: Oxford University Press.
      • Darwin, C .; Wallace, Alfred R. (1858). On the tendency of species to form varieties; and on the perpetuation of varieties and species by natural means of selection. Journal of Proceedings of the Linnean Society of London. Zoology 3.3 (9): pages 46 to 50.
      • Hull, DL (1967). The metaphysics of evolution. The British Journal for the History of Science. Cambridge: Cambridge University Press on behalf of the British Society for the History of Science. 3 (4): 309-337.
      • Kutschera, U .; Karl J .; Niklas (2004). Modern Theory of Biological Evolution: An Extended Synthesis. Naturwissenschaften, 91 (6): pages 255-276.
      • Mayr, E. (1982). The growth of biological thought: diversity, evolution and heritage. Cambridge: The Belknap Press and Harvard University Press.

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