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

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

It is not surprising that our ancestors also wondered about the animals and plants they saw around: were they always like this or if they have been changing over time? And if there were differences, What are the mechanisms that have been used to carry out these modifications?

These are the main unknowns that have been tried to solve through what we know today as the theory of biological evolution, which is at the base of biology and communicates with much of the realm of psychology, when talking about the origin of certain innate tendencies that could be influencing our behavior and the way we work. think. Let's see what it consists of.

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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

. That is, biological evolution is a process observed in reality (even in contexts experimental), and the theory of evolution is a set of "riddles" to understand this natural phenomenon.

It should be remembered that a scientific theory is the highest value status that a system of scientific laws and hypotheses can adopt. interconnected with each other when they have been tested successfully many times and what they help to understand cannot be expressed mathematically. This means, among other things, that although the theory of evolution is "only" a theory, to refute it it would be necessary to create another alternative theory; Today, this hypothetical second theory does not exist, and that is why it is the basis of Biology and current biomedical sciences in general.

On the other hand, the theory of evolution as we understand it today cannot be separated from the research and discoveries of Charles Darwin, but it is not limited to these. Today the scientific community goes beyond Darwin's proposals, although starting from them and without denying their fundamental elements, and combining this knowledge with that of the world of Genetics as a field of research. But to better understand what this theory is like, let's start at the beginning: its beginnings and precedents.

Until the 19th century, the predominant idea about the origin of species was creationism. According to this doctrine, an all-powerful entity had created each of the existing living beings, and these had not changed over time. These kinds of beliefs trace their origins to Ancient Greece, and although they never became hegemonic in Europe, they left their mark on the thinking of some theorists and intellectuals.

But with the Enlightenment period, more complex theories and closer to reality began to emerge in Europe. The most remarkable at the beginning of the 19th century was the one proposed by Jean-Baptiste Lamarck; This French naturalist proposed that all species had the will to change and the ability to transfer these to their offspring. changes acquired through their actions, a characteristic transmission mechanism known as character inheritance acquired.

Of course, it should be noted that Lamarck's ideas were not based on the inheritance of traits present in the 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 the actions performed proactively: for example, attempting to switch from a rodent-based diet to one based on fishes.

Lamarck, in opposition to the creationists, defended the idea of ​​the evolution of species, but accepted that species generated spontaneously and did not have a common origin. That is, his theory spoke only of the mechanism by which living things change over time, and not about how they first arise. I will not go on any longer, since you have a very complete article on Lamarckism here: "Lamarck's Theory and the Evolution of Species".

Charles Darwin and the theory of biological evolution

He had taken a big step in admitting the idea of ​​biological evolution through totally natural mechanisms, but Lamarck's theory had many fissures. It was not until 1895 that the British naturalist Charles Darwin published the book The origin of species, in which he proposed a new theory of evolution (which would become known as Darwinism). Little by little, this theory would take shape in his successive writings, and it would be seen that it explained the biological evolution through a natural mechanism: natural selection combined with selection sexual. Then we will see what they consist of.

Along with fellow British naturalist Alfred Russel Wallace, (who curiously conducted similar research and reached almost identical conclusions without having spoken a word with him), Darwin put forward new ideas in favor of the evolution; Of course, with great caution, because the implications of his work put the establishment of the Church, which had always attributed to the direct intervention of God the existence of all forms of lifetime.

Natural selection

According to Darwin, all species come from a common origin, from which they diversified thanks, in part to natural selection. This evolutionary mechanism can be summarized in that the species better adapted to the environment in which they are, reproduce more success and have offspring that, in turn, have a better chance of reproducing successfully, giving way to 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, in many cases reaching disappear.

Thus, in the first place, populations of living beings with different characteristics appeared on the scene, and the environment exerted pressure on them. that made some of them have more reproductive success than others, causing their characteristics to spread and making them disappear other

What characterized this process was its natural character, oblivious to the influence of a supernatural entity. to direct it; It happened automatically, in the same way that a snowball gets bigger by the influence of the force of gravity applied on the side of a mountain.

Sexual selection

Another of the evolutionary mechanisms that Darwin's theory of evolution describes is sexual selection, which consists of the set of dispositions natural and behavioral patterns that make certain individuals more desirable to have offspring with them, and others less desirable to have offspring with them. the same.

A) Yes, sexual selection plays a double game. On the one hand, it is complemented by natural selection, because it provides elements that explain why certain individuals have greater reproductive success than others; but on the other hand it works against him, since there are traits that can be advantageous from the point of view of sexual selection, but disadvantageous from the point of view of sexual selection (that is, the result of the interaction with the environment, with the exception of possible partners reproductive).

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

Neo-Darwinism

Despite removing the divinity in creation and explaining a basic mechanism by which species are changing and diversifying Over time, Darwin was unaware of the term we know today as genetic variability, and he was not aware of the existence of genes. In other words, he did not know how the variability of characteristics appeared, on which the pressure of natural selection acts. For this reason, he never completely rejected Lamarck's idea of ​​the inheritance of acquired characters.

Unlike Darwin, Wallace never accepted this idea, and from this dispute appeared a new evolutionary theory called Neo-Darwinism., driven by the naturalist George John Romanes, who in addition to rejecting Lamarckian ideas in their entirety, believed that the only evolutionary mechanism was natural selection, something that Darwin never maintained. It was not until the beginning of the 20th century when Mendel's laws were accepted, showing that mutations in DNA are pre-adaptive, that is, first a mutation and then it is put to the test whether the individual in which it has occurred is better adapted to the environment or not, breaking the idea of ​​the inheritance of characters acquired.

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

The social impact of the theory of evolution

The biggest problem that Darwin had was to dispense with the figure of the hand of God in his theory about what the mechanism could be explanatory of biological diversity, something unforgivable in times when religion and creationism were hegemonic.

However, Charles Darwin's theoretical legacy was robust, and over the years the appearance of new fossils gave good empirical support to his theory... which did not make his contribution to science seen with better eyes from religious instances. Even today environments closely linked to tradition and religion deny the theory of evolution, or else they consider it “simply a theory”, implying that creationism enjoys the same endorsements scientists. Which is a mistake.

Evolution is a fact

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

Below you can find several of the proofs that prove the existence of biological evolution.

1. Fossil record

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 current species, but at the same time, they have a certain resemblance. It sounds weird but with an example it will be easier to understand.

The Glyptodon It was a Pleistocene mammal that bears a remarkable resemblance to a current armadillo but in a giant version: it is a trace of the evolutionary tree that leads to the current armadillos. The same fossils are also proof of extinction, since they show that in the past there were organisms that today are no longer among us. The most iconic example is dinosaurs.

2. Vestiges and imperfect designs

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

This is one more proof of evolution that, in addition, reveals that this process is opportunistic, since it takes advantage of what it has at hand to organize a new organism. The species of life are not the result of an intelligent and well-planned design, but are based on functional "bungles" that are perfected (or not) over the generations.

3. Homologies and analogies

When comparing the anatomy between different organisms, we can find cases that, once again, are proof of evolution. Some of them are consist of homologies, in which two or more species present a similar structure in some of the parts of their anatomy, but they are to perform different functions, which is explained because they come from the same predecessor. An example are the extremities of tetrapods, since they all have a structural arrangement similar despite the fact that their limbs have different functions (walking, flying, swimming, jumping, etc.).

The other case is analogies, organs of different species that do not have the same anatomy but do share a function. A clear example are the wings of birds, insects and flying mammals. They have been developed in different ways to reach the same function, that of flying.

4. DNA sequencing

Finally, the genetic code, with some exceptions, is universal, that is, every organism uses it. If it were not, it would not be possible for E.coli bacteria could produce human insulin by introducing into it the gene (of human origin) responsible for generating this substance, as we do today. Furthermore, GMOs are another evidence that the genetic material of all life forms has the same nature. Other evidence that all species have a common origin and proof of evolution.

Evolutionary mechanisms

Although we have discussed natural selection as a mechanism that evolution uses to advance, it is not the only one that is 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 with Darwin, this naturalist originated the idea of ​​natural selection from his observations in the Voyage of the Beagle during his journey through the Galapagos Islands. In them, he caught her attention that each island had its own species of finch, but they all had a similarity between them and those found on the neighboring continent, South America.

The conclusion he reached is that the island finches originally came from the mainland, and that upon reaching each island suffered an "adaptive radiation", in this case by food, thus generating a range of variants starting from the same group of ancestors; thus, These birds have very different beaks, having adapted to the ecosystem of each island separately..

Today we can better clarify how natural selection works. The environment is not stable and changes over time. Species undergo mutations in their genome randomly, and these make them change their characteristics. This change can favor their survival or, on the contrary, make life difficult and cause them to die without children.

2. Artificial selection

It is not properly an evolutionary mechanism, but it is a variety of natural selection. It is said artificial, since it is the human being who directs evolution for his own interests. We are talking about a practice that has occurred in agriculture and livestock for millennia, choosing and crossing plants and animals to obtain greater productivity and performance. It also applies to domestic animals, such as dogs, where other characteristics were sought, such as more strength or more beauty.

3. Genetic drift

Before talking about this mechanism, we must know the concept of allele. An allele consists of all the mutational forms of a particular gene. For example, the different genes for eye color in man. Genetic drift is defined as a random change in allelic frequency from one generation to another, that is, the environment does not act. This effect is best appreciated when the population is small, as in the case of inbreeding., where genetic variability is reduced.

This mechanism can delete or set characteristics randomly, without the need for the environment to act on their selection. And therefore, in small populations, it is easier for a quality to be lost or gained by chance.

• You may be interested in: "Genetic drift: what is it and how does it affect biological evolution?"

Evolution-related controversy

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 are against it because it is considered that it contains certain deficiencies or concepts that are not explained or are not included.

1. Neutralism

Until recently, it was thought that only harmful mutations (negative selection) and beneficial mutations (positive selection) existed. But the Japanese biologist Motoo Kimura affirmed that at the molecular level there are many mutations that are neutral, that are not subjected to no selection and whose dynamics depend on the rate of mutation and the genetic drift that eliminates them, creating a Balance.

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

2. Neolamarckism

Neo-Lamarckism is the part of the scientific community that still maintains that Lamarck's theory and its inheritance of acquired characters cannot be ruled out. From there, an attempt is made to reconcile this idea with genetics, stating that mutations are not random but are the consequence of the "effort" of the species to adapt to the environment. However, its empirical basis cannot be compared to that of synthetic theory.

Bibliographic references:

• Cracraft, J.; Donoghue, M.J. (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 the Proceedings of the Linnean Society of London. Zoology 3. 3 (9): pp. 46 - 50.
• Hull, D.L. (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). The modern theory of biological evolution: an expanded synthesis. Naturwissenschaften, 91 (6): pp. 255 - 276.
• Mayr, E. (1982). The Growth of Biological Thought: Diversity, Evolution, and Inheritance. Cambridge: The Belknap Press of Harvard University Press.