4 EVIDENCES OF THE EVOLUTION OF LIVING BEINGS - BIOLOGY - 2024

The evidence for evolution consists of a series of tests to confirm the change process during the passage of time in biological populations. This evidence comes from different disciplines, from molecular biology to geology.

Throughout the history of biology, a series of theories were devised that tried to explain the origin of species. The first of these is the fixist theory, devised by a number of thinkers, dating from the time of Aristotle. According to this body of ideas, species were created independently and have not changed since the beginning of their creation.

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Subsequently, the transformist theory was developed which, as its name suggests, suggests the transformation of species over time. According to the transformists, although species were created in separate events, they have changed over time.

Finally, we have the evolutionary theory, which in addition to proposing that species have changed over time, considers a common origin.

These two postulates were organized by the British naturalist Charles Darwin, reaching the conclusion that living beings originated from ancestors very different from them and are related to each other by common ancestors.

Before Darwin's time, fixist theory was mainly used. In this context, the adaptations of animals were conceived as creations of a divine mind for a specific purpose. Thus, birds had wings to fly and moles had legs to dig.

With the arrival of Darwin, all these ideas are discarded and evolution begins to make sense of biology. Next we will explain the main evidences that support evolution and help to rule out fixity and transformism.

The fossil record and paleontology

What is a fossil?

The term fossil comes from the Latin fossilis, which means "from a pit" or "from the earth." These valuable fragments represent for the scientific community a valuable “look into the past”, literally.

Fossils can be the remains of animals or plants (or another living organism) or some trace or mark that the individual left on a surface. The typical example of a fossil is the hard parts of an animal, such as the shell or the bones that were transformed into rock by geological processes.

Also the “traces” of organisms can be found in the registry, such as burrows or tracks.

In ancient times, fossils were thought to be a very peculiar type of rock that had been shaped by environmental forces, be it water or wind, and spontaneously resembled a living being.

With the rapid discovery of a vast number of fossils, it became clear that these were not simply rocks, and the fossils came to be considered the remains of organisms that had lived millions of years ago.

The first fossils represent the famous "fauna of Ediacara". These fossils date from about 600 million years ago.

However, most of the fossils date from the Cambrian period, roughly 550 million years ago. In fact, the organisms of this period are mainly characterized by enormous morphological innovation (for example, the immense number of fossils found in the Burguess Shale).

Why are fossils evidence of evolution?

It stands to reason that the fossil record - a vast caravan of diverse shapes that we no longer observe today, and that some are extremely similar to modern species - belies the fixist theory.

Although it is true that the record is incomplete, there are some very particular cases where we find transitional forms (or intermediate stages) between one form and another.

An example of incredibly conserved forms on the record is the evolution of cetaceans. There is a series of fossils that show the gradual change that this lineage has undergone over time, starting with a four-legged land animal and ending with the huge species that inhabit the oceans.

Fossils showing the incredible transformation of whales have been found in Egypt and Pakistan.

Another example that represents the evolution of a modern taxon is the fossil record of the groups that originated today's horses, from an organism the size of a canid and with teeth to browse.

Similarly, we have very specific fossils of representatives that may have been the ancestors of tetrapods, such as Ichthyostega - one of the earliest known amphibians.

Homology: evidence of common origin

What is homology?

Homology is a key concept in evolution and in the biological sciences. The term was coined by the zoologist Richard Owen, and he defined it as follows: "the same organ in different animals, in whatever form and function."

For Owen, the similarity between the structures or morphologies of the organisms was due solely to the fact that they corresponded to the same plan or "arotype".

However, this definition was prior to the Darwinian era, for this reason the term is used in a purely descriptive way. Later, with the integration of Darwinian ideas, the term homology takes on a new explanatory nuance, and the cause of this phenomenon is a continuity of information.

Homologies are not easy to diagnose. However, there is certain evidence that tells the researcher that he is facing a case of homology. The first is to recognize if there is a correspondence in terms of the spatial position of the structures.

For example, in the upper limbs of tetrapods the relationship of the bones is the same between the individuals of the group. We find a humerus, followed by a radius and an ulna. Although the structure may be modified, the order is the same.

Are all similarities homologies?

In nature, not all similarities between two structures or processes can be considered homologous. There are other phenomena that lead to two organisms that are not related to each other in terms of their morphology. These are evolutionary convergence, parallelism, and reversal.

The classic example of evolutionary convergence is the eye of vertebrates and with the eye of cephalopods. Although both structures fulfill the same function, they do not have a common origin (the common ancestor of these two groups did not have a structure similar to the eye).

Thus, the distinction between homologous and analogous traits is vital to establish relationships between groups of organisms, since only homologous traits can be used to make phylogenetic inferences.

Why are homologies proof of evolution?

Homologies are proofs of the common origin of species. Returning to the example of the quiridium (member formed by a single bone in the arm, two in the forearm and the phalanges) in tetrapods, there is no reason why a bat and a whale should share the pattern.

This argument was used by Darwin himself in The Origin of Species (1859), to refute the idea that species were designed. No designer - no matter how inexperienced - would use the same pattern on a flying organism and an aquatic one.

For this reason, we can conclude that the homologies are evidences of common ancestry, and the only plausible explanation that exists to interpret a quiridium in a marine organism and in another flying one, is that both evolved from an organism that already had this structure.

What are molecular homologies?

So far we have only mentioned morphological homologies. However, homologies at the molecular level also serve as evidence for evolution.

The most obvious molecular homology is the existence of a genetic code. All the information necessary to build an organism is found in DNA. This becomes a messenger RNA molecule, which is finally translated into proteins.

The information is in a three-letter code, or codons, called the genetic code. The code is universal for living beings, although there is a phenomenon called codon use bias, where certain species use certain codons more frequently.

How can it be verified that the genetic code is universal? If we isolate mitochondrial RNA that synthesizes the homoglobin protein from a rabbit and introduce it into a bacterium, the prokaryote's machinery is able to decode the message, although it does not naturally produce hemoglobin.

Other molecular homologies are represented by the enormous number of metabolic pathways that exist in common in different lineages, widely separated in time. For example, the breakdown of glucose (glycolysis) is present in virtually all organisms.

What do molecular homologies teach us?

The most logical explanation for why the code is universal is a historical accident. Like language in human populations, the genetic code is arbitrary.

There is no reason why the term "table" should be used to designate the physical object of the table. The same applies to any term (house, chair, computer, etc).

For this reason, when we see that a person uses a certain word to designate an object, it is because he learned it from another person - his father or mother. And these, in turn, learned it from other people. That is, it implies a common ancestor.

Similarly, there is no reason for valine to be encoded by the series of codons that associate with this amino acid.

Once the language for the twenty amino acids was established, it stuck. Perhaps for energy reasons, since any deviation from the code could have deleterious consequences.

Artificial selection

Artificial selection is a test of the performance of the natural selection process. In fact, variation in domestic status was crucial in Darwin's theory and the first chapter on the origin of species is devoted to this phenomenon.

The best known cases of artificial selection are the domestic pigeon and dogs. This functional process through human action that selectively chooses certain variants from the population. Thus, human societies have been producing the varieties of livestock and plants that we see today.

For example, characteristics such as the size of the cow can be rapidly altered to increase meat production, the number of eggs laid by hens, and milk production, among others.

As this process occurs quickly, we can see the effect of selection in a short period of time.

Natural selection in natural populations

Although evolution is considered a process that takes thousands or in some cases even millions of years, in some species we can observe the evolutionary process in action.

Antibiotic resistance

A case of medical importance is the evolution of resistance to antibiotics. The excessive and irresponsible use of antibiotics has led to an increase in resistant variants.

For example, in the 1940s, all variants of staphylococci could be eliminated with the application of the antibiotic penicillin, which inhibits cell wall synthesis.

Today, almost 95% Staphylococcus aureus strains are resistant to this antibiotic and others whose structure is similar.

The same concept applies to the evolution of the resistance of pests to the action of pesticides.

The moth and the industrial revolution

Another very popular example in evolutionary biology is the Biston betularia moth or birch butterfly. This moth is polymorphic in terms of its coloration. The human effect of the Industrial Revolution caused a rapid variation in the allele frequencies of the population.

Previously, the predominant color in moths was light. With the advent of the revolution, pollution reached staggeringly high levels, darkening the bark of birch trees.

With this change, moths with darker colors began to increase their frequency in the population, since for camouflage reasons they were less showy to birds - their main predators.

Human activities have significantly affected the selection of many other species.

References

1. Audesirk, T., Audesirk, G., & Byers, BE (2004). Biology: science and nature. Pearson Education.
2. Darwin, C. (1859). On the origins of species by means of natural selection. Murray.
3. Freeman, S., & Herron, JC (2002). Evolutionary analysis. Prentice Hall.
4. Futuyma, DJ (2005). Evolution. Sinauer.
5. Soler, M. (2002). Evolution: the basis of Biology. South Project.