BIOLOGICAL EVOLUTION: THEORIES, PROCESS, PROOFS AND EXAMPLES - BIOLOGY - 2025

The biological evolution is change in the properties of groups of organisms in the course of generations. Groups of organisms of the same species are known as "biological populations."

In essence, the modern neo-Darwinian theory of evolution says that evolution consists of a gradual change of life forms. It started - presumably - with a molecule with the ability to replicate itself about 3.5 billion years ago.

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Over time, a branching of lineages occurred and new and diverse species emerged. The mechanisms for this evolutionary change are natural selection and gene drift.

Evolutionary biology seeks to understand the origin of biological diversity and how it is maintained. As it is a central science in biology, it is generally considered as a unifying thought, which integrates the different disciplines of the biological sciences.

This unifying property of evolutionary biology was marked in the famous phrase of Theodosius Dobzhansky: "nothing makes sense in biology, except in the light of evolution."

Today, evolutionary biology has enjoyed all the advances in science, allowing the reconstruction of phylogenies using numerous molecular characters and powerful statistical analysis.

What is the evolutionary process?

Evolution is a term derived from Latin roots evolvere, which translates to unfolding or revealing a hidden potential. Today, the word evolution simply evokes a change. It is probably part of our daily lexicon to refer to changes in an object or a person.

However, biological evolution refers to changes in groups of organisms through the passage of generations. This general definition of evolution is used by Futuyma (2005). It is important to note that organisms as individuals do not evolve, while groups of organisms do.

In biology, the set of individuals of the same species that coexist in time and space are called populations. For a change in a population to be considered evolutionary, it must be passed from one generation to another via genetic material.

Scientific theories of evolution

Since time immemorial, the human being has felt an intrinsic curiosity about the origin of life and the existence of the enormous diversity that organic beings present.

As the British naturalist Charles Darwin (1809-1882) had a significant impact on the development of this science, we will examine the theories proposed before and after his contributions.

Before Darwin: creationism and the immutability of species

Before Darwin, naturalists and other scientists were characterized by a creationist thinking regarding the origin of species.

Essentialist visions were handled, where each species had an immutable essence and the variation that we observed in the group was only due to imperfections of being. This conception was handled in the time of Plato and Aristotle.

Time later, Christians began to interpret the passages of the Bible literally, understanding that organic beings were created in a single event by a supernatural entity. This conception did not allow changes in the species over time, since they had been created under divine perfection.

In the 18th century the goal of naturalists was to catalog the divine plan that God had created. For example, Linnaeus laid the foundations for current taxonomy by following this line of thought.

Later this view was challenged by various thinkers. The most relevant pre-Darwinian theory of the time was formulated by Jean Baptiste Lamarck. For him, each species had originated individually through spontaneous generation and was capable of "progressing" or improving over time.

One of the most relevant principles established by Lamarck was the inheritance of acquired characters. This naturalist believed that the different traits that we acquire throughout our lives could be passed on to our offspring.

For example, under the Lamarkian view, a bodybuilder who works hard all his muscle groups, had to have children with developed muscles. The same principle would apply with the disuse of organs.

Darwin and Wallace's contributions to evolutionary biology: natural selection

Charles Darwin's name appears in most biology texts, regardless of his specialty. Darwin revolutionized biology, and science in general, to an incredible extent - comparable, for example, to Newton's contributions.

In his youth, Darwin kept a thought faithful to the biblical teachings. However, accompanied by a religious thought, Darwin expressed an interest in the natural sciences, which is why he surrounded himself with the most brilliant scientific minds of the moment.

The journey on the Beagle

Darwin's life took a turn when at an early age he began a journey aboard the HMS Beagle, a British ship that would explore different regions of South America. After a journey that lasted a couple of years, Darwin observed and collected an enormous diversity of South American fauna and flora.

Thanks to his optimal financial situation, Darwin was able to dedicate his life exclusively to his work in the biological sciences. After extensive meditations - and also lectures on economics - Darwin generated his theory of natural selection.

Natural selection is a simple and powerful idea, being an important evolutionary mechanism - although not the only one, as we will see later.

This idea was not solely deduced by Darwin. A young naturalist named Alfred Wallace independently came up with very similar ideas. Wallace communicated with Darwin, and the two together presented the theory of evolution by natural selection.

The origin of species

Later, Darwin presents his masterpiece: "The Origin of Species", which unfolds his theory in detail and with robust evidence. This book has six editions that Darwin worked on throughout his life.

The theory of natural selection holds that if there is some useful and heritable variation in a population of individuals, there will be a differential reproduction between the possessors of the characteristic. These will tend to generate more offspring, thus increasing the frequency of the trait in the population.

Furthermore, Darwin also proposed common ancestry: all species have diverged in evolutionary time from a common ancestor. Thus, all organic beings can be represented in the great tree of life.

After Darwin: Neo-Darwinism and Synthesis

Immediately after the publication of "The Origin", a great controversy broke out among the most important scientists of the time. However, as the years passed, the theory was gradually accepted.

There were biologists who never accepted Darwinian ideas, so they generated their own evolutionary theories, today almost completely discredited. Examples of this are neo-Lamarkism, orthogenesis, and mutationism, among others.

Between the 30's and 40's all anti-Darwinian theories were discarded with the advent of evolutionary synthesis. This consisted of the union of Darwinian ideas with the contributions of a series of geneticists and paleontologists such as Fisher, Haldane, Mayr, and Wright, among others.

The synthesis managed to unify evolutionary theories with correct genetic principles, since one of the difficulties that Darwin had to experience during his work was the ignorance of genes as particles of heredity.

Evidence for evolution: just a theory?

Today, biological evolution is a fact backed by robust and abundant evidence. Although biologists do not doubt the veracity of the process, in everyday life we ​​hear that evolution is "just a theory" - with pejorative connotations.

This misunderstanding stems from the fact that the term "theory" has different meanings in science and in everyday life. For most people, a theory is an uncertain prediction of a fact, characterized by a weak foundation. For a scientist, a theory is a body of coherent and properly structured ideas.

Following this order of ideas, we can conclude that evolution is a fact, and there are mechanisms to explain it, such as the theory of natural selection. The most outstanding evidences of the evolutionary process are the following.

Homology

Two processes or structures are homologous if said trait was inherited directly from a common ancestor. In evolutionary biology, homology is a fundamental point, since they are the only characteristics that allow us to reconstruct ancestor-descendant relationships between groups.

Morphological homologies

A very famous example of homology is the limb bones of tetrapods. Let's take three animals that differ in their mode of locomotion to understand why homology is robust evidence of the evolutionary process: humans, whales, and bats.

These three groups share a basic structural plan in their forelimbs, because they inherited it from a common ancestor. That is, an ancestral tetrapod had a humerus, followed by a radius and an ulna, and finally a series of phalanxes.

There is no functional reason why three animals with such disparate lifestyles should share the same plan of bones in their limbs.

If life were designed, there is no reason to build an aquatic, a flying, and a terrestrial organism with the same plan. No engineer - no matter how inexperienced - would create a flying and a swimming organism in the same way.

The most logical way to explain this is by common ancestry. All three inherited this structural plan from an ancestor and underwent the adaptive modifications we see today: wings, fins, and arms.

Molecular homologies

Homologies are not restricted to anatomical features of a living being. They can also be evidenced at the molecular level. The genetic information of living beings is stored in DNA and is translated in the form of triplets: three nucleotides correspond to one amino acid.

A universal molecular homology is the reading of this genetic code, since virtually all organic beings share this language - although there are very specific exceptions.

The fossil record

When Darwin proposes his theory of natural selection, he argues that all gradual transitional forms are not present in the fossil record because it is incomplete. In contrast, opponents of Darwinian ideas see the discontinuity of the record as proof against the theory.

We must remember that the fossilization process of an organic being is an unlikely event, coupled with the probability that a specimen found in good condition. For these reasons, less than 1% of all the forms that ever lived are represented in the fossil record.

Despite this, very well preserved fossils have been found that serve as a “window to the past”. One of the most famous is Archeopteryx. In this fossil, the intermediate characteristics between a reptile and a bird stand out. Likewise, we have several hominid fossils that have allowed us to reconstruct the evolution of humans.

Some alternative theories have been proposed to explain the discontinuity of the register, such as the theory of punctuated equilibrium.

Biogeography

Although evolution is supported by evidence from many branches of knowledge, it was biogeography that convinced Darwin of the veracity of the evolutionary process.

The distribution of living organisms on planet earth is not homogeneous, and many aspects of this pattern can be explained by evolutionary theory - and not by the special creation hypothesis.

When we examine the fauna of oceanic islands (isolated elements that have never had contact with the mainland), we find that the species composition is very peculiar. For example, this can be seen on islands located in the North Atlantic, called the Bermuda Islands.

The vertebrates (non-marine) native to the area are very few, mainly birds, migratory bats, and lizards, among others. Some of these species show a significant relationship with the fauna of North America. Others, for their part, are endemic to the island and are not found in any other region.

This distribution pattern is compatible with evolutionary processes, since the area is specifically colonized with animals capable of flight and of dispersing great distances.

Evolution in action: example of evolution

Another misunderstanding in evolutionary biology is that it is related to an extremely slow process.

While it is true that to obtain complex adaptations such as powerful jaws or eyes with excellent vision, we would have to wait a couple of million years, there are certain evolutionary processes that we can observe with our own eyes in a relatively short period of time.

Next we will analyze the case of the Biston betularia moth as an example of evolution in action. Later we will talk about resistance to antibiotics and pesticides, another example of evolution that we can observe in a short space of time.

Industrial melanism and

One of the most prominent examples in evolutionary biology is industrial melanism. This phenomenon was documented during the industrial revolution and managed to establish a relationship between the variation in the coloration of the Biston betularia moth and the contamination of its habitat.

The moth has two morphologies: one light and one dark. Before contamination, the dominant variant was the light moth, presumably because it perched on the light bark of birch trees and could go unnoticed by potential predators - birds.

With the advent of the industrial revolution, pollution increased to significant levels. The bark of the trees began to take on an increasingly dark color and this generated a change in the frequencies of the light and dark variants of the moths.

The dark moth was the dominant variant for a time, as it could better hide in the blackened bark.

Subsequently, environmental cleanup programs were implemented that helped reduce environmental pollution. Thanks to the efficiency of these programs, the trees began to regain their original characteristic color.

As we can guess, the frequency of the moths changed again, the clear variant being the dominant one. Thus, the evolutionary process was documented in a period of time of 50 years.

Mechanisms of evolution

Biological evolution is a process that involves two steps: the generation of the variation and then the differential reproduction of the variations, either by natural selection or by genetic drift. For this reason, the terms natural selection and evolution should not be used interchangeably - because they are not.

From the perspective of population genetics, evolution is the change in allelic frequencies over time within a population. Thus, the forces that change allele frequencies are selection, drift, mutation, and migration.

Natural selection

As we mentioned earlier, Darwin's greatest contribution to biology was proposing the theory of natural selection. This has been strongly misinterpreted and misrepresented by the media, associating it with wrong phrases such as: "survival of the fittest."

Conditions for natural selection to occur

Natural selection is a simple idea, with magnificent results. If a system meets the following characteristics, it will evolve - inevitably - through natural selection:

Evolutionary Biology Applications

Evolutionary biology has a number of applications, both for medicine, agriculture, conservation biology, and for other disciplines.

Medicine

The theory of evolution is an essential science in the field of medicine. For example, it allows us to predict the outcome of the indiscriminate use of antibiotics for the treatment of infectious diseases.

When we apply an antibiotic unnecessarily or do not complete medical treatment, we will eliminate non-resistant variants, but resistant individuals will increase their frequency in the bacterial population.

Currently, the issue of bacterial resistance to most antibiotics is a topic of global interest and concern. Raising awareness about the use of antibiotics is one way to reduce this complication.

For example, the bacteria Staphylococcus aureus is common in operating rooms and causes infections in patients during surgeries.

Today, the bacteria are fully resistant to a number of antibiotics, such as penicillin, ampicillin, and related drugs. Although new antibiotics have been generated to counteract it, the drugs are less and less efficient.

The crisis of resistance is one of the most dramatic examples of evolution, which we can observe with our own eyes, so it also serves as evidence of the evolutionary process.

Agriculture and Livestock

The same evolutionary principle can be extrapolated to the use of pesticides for the elimination of pests, in crops with significant economic importance. If the same type of pesticide is applied for a long time, we will favor the increase of resistant variants.

Similarly, farmers seek to obtain the "best" animals that maximize production (of milk, meat, etc). These ranchers select the individuals they find most useful in practical terms. As the generations go by, individuals increasingly resemble what is desired by humans.

This process of human artificial selection resembles natural selection, in terms of differential reproductive success. With the notable difference that in nature there is no selection entity.

Conservation biology

Regarding conservation issues, understanding phenomena such as "bottlenecks" and the decrease in fitness caused by inbreeding makes it possible to avoid them and generate conservation plans that increase fitness and keep the population "healthy".

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