Introduction to evolution

The word evolution is used to describe gradual progressive developments. In the case of living organisms, evolution can be defined as the development of complex organisms from preceding simpler organisms over time. The concept of evolution did not originate with Darwin and his book "The Origin of Species." Long before Darwin, scientists and philosophers had proposed various evolutionary hypotheses and attempts to explain the structural and functional similarity of living organisms. Such ideas evolved themselves as science progressed. In this topic, we will talk about biological evolution, or the evolution of species.

What is evolution

Let's start with an example: to visualize evolution without waiting millions of years, we should observe a simple organism that can reproduce at an enormous rate and go through many many generations in a more practical time frame. That is exactly what evolutionary scientists from the University of Michigan thought, and so they set up an experiment using the bacteria E. coli. They divided the initial population into 12 flasks, and began growing them and observing.

The experiment began in 1988, and in 2008, it was found that one of the populations was developing faster than the others. In this flask, the bacteria lived on nutrient media that contained not only the glucose familiar to bacteria, but also a substance that E. coli cannot typically digest, sodium citrate. Over the years of the experiment, the bacteria learned to digest the citrate and extract energy from it in addition to glucose. That's why this population grew faster than the other eleven, which fed on glucose alone.

It took 20 years and 31,500 generations for the mutation to occur that enabled the bacteria to adapt to their environment and use the local food source. Translated into human time, this is about 800,000 years. By comparison, Homo erectus appeared about 1.9 million years ago and Homo sapiens (that is, you and I) about 200,000 years ago.

So, let's begin to define evolution: biological evolution is a long process by which living things change under the influence of changing external conditions.

• Morphological changes — new tissues (germ leaves), organs and organ systems appeared;

• Physiological changes — the simplest processes were being added, complicated, and improved;

• Genetic changes in populations of living organisms;

• Macro-level (macro-evolution): appearance of new types, divisions, classes of living organisms, etc.;

• Micro-level: the formation of new species;

Evolution refers not only to the formation of something new, but also to the simplification in the structure or the disappearance of the old — for example, the extinction of some species of living organisms (unfortunately, this process continues today).

Evolution goes (yes, it is still going on!) in two directions:

• Biological progress ("victory" of a species or another group in the struggle for existence). Its signs are: increase in the number of individuals of a given group, expansion of its range, formation of new populations, species, subspecies.

• Biological regression (lag in the rate of group evolution from the rate of environmental changes). Its signs are: decrease in the number of individuals of the group, narrowing of the habitat range, reduction of population and species diversity. Biological regression can lead a species to extinction.

The history of the concept of evolution

Contemplation of evolution emerged in ancient philosophical systems, when the first ideas of the natural development of living nature were being described and recorded.

In more recent times, Darwin's theory was preceded by the work of Carl Linnaeus, who proposed the first classification of living organisms based on the comparison of individual characteristics. He also introduced a binary nomenclature and described more than 10,000 biological species.

The first evolutionary doctrine was created by Jean Baptiste Lamarck. He understood evolution as a process of gradual complication of organisms from the lowest to the highest, showed the adaptive nature of acquired changes, and believed that new species of living organisms are constantly being formed.

The impetus for the recognition of evolution by the scientific community was the 1859 publication of Charles Darwin's "The Origin of Species by Natural Selection, or the Preservation of Favored Species in the Struggle for Life," which allowed a complete rethinking of the idea of evolution, backed by experimental data from numerous observations. Later, the synthesis of classical Darwinism with the achievements of genetics led to the creation of the modern synthetic theory of evolution.

The Modern Synthetic Theory of Evolution

The modern synthetic theory of evolution (Modern synthesis) is based on the same ideas proposed by Darwin. However, it is supplemented with information from other biological sciences like genetics, ecology, molecular biology, systematics, etc.

Evolution in the modern synthesis is defined as a gradual process of changes in the gene pool of populations: allele frequencies of different genes change, new alleles and genes appear, others disappear.

Genetic mutations occur all the time, but not all of them are fixed in the course of evolution. Getting a useful mutation is comparable in probability to winning the lottery, but such mutations give the species an advantage in the struggle for existence, allowing it to leave more viable offspring.

According to the modern synthetic theory of evolution, the elementary unit of evolution is the population.

According to Modern synthesis, there are several main evolutionary factors:

• Natural selection is the most important factor in the evolutionary process. As a result of natural selection, the genotypes most adapted to a given environment reproduce to a greater extent.

• Competition for existence. Darwin considered this to be the main factor in evolution, and natural selection is already a consequence of the struggle for existence.

• The mutation process results in new genetic material (new alleles of genes or even new genes). Although mutations are rare and most often harmful, they are much of the material for the action of natural selection.

• Gene flow is the change in allele frequencies in populations due to the migration of individuals. In addition, gene flow leads to gene exchange between different populations, which reduces the likelihood of their divergence during speciation.

• Gene drift involves changes in allele frequencies due to random causes. Such causes include fluctuations in the population size, its age and sex composition, changes in the food supply, presence or absence of competition, etc.

• Isolation — the emergence of barriers between populations, preventing the interbreeding of individuals and the exchange of genes. As a result, each population can follow its own evolutionary path.

Evidence of Evolution

Three groups can be distinguished among the evidence for evolution.

1. The first is the documented examples of small changes in species observed over geologically short periods of time in the wild and as a result of the selection of agricultural plants and domestic animals. As an example, Albert Fearn's letter described the change in coloration of the pepper moth. The white pepper moth and other butterflies around the English town of Lewes had drastically changed their color, turning coal-black. Fearn suggested that this change in their appearance was due to the fact that lime factories had appeared in Lewes a few decades earlier, which smoked out the surrounding birch forests and limestone deposits with large amounts of soot. As a result, it became much easier for birds to find light-colored butterflies, making them more visible on dark tree trunks, while dark moths, by contrast, became invisible to them. Thus, in polluted areas, the dark butterflies received a more useful mutation. In environmentally friendly areas, however, light-colored specimens predominated.

2. The second is the paleontological record, evidence of significant variability in life throughout Earth's history .

3. The third group of evidence includes morphological features of the structure of all existing modern organisms, such as rudimentary organs and atavisms, which allow us to make verifiable assumptions about the common origin of particular species

Evidence of evolution can also be grouped in other ways:

• Embryological evidence of evolution. The striking similarity of vertebrate animal embryos was brought to the attention of many researchers long before Darwin. In 1828, Carl Baer introduced the law of embryonic similarity, which is based on the similarities in structure of early embryos from animals of different species. Particular similarity of embryonic developmental stages is observed within types or classes. E. Heckel and F. Müller independently formulated the biogenetic law, which states that ontogenesis (individual development of an organism) repeats phylogeny (its historical development). Later, the biogenetic law was developed and clarified by the Russian scientist A.N. Severtsov, who established that embryogenesis repeats the characteristics of embryos and not of adults. For a long time it was considered as one of the main proofs, but now it is being abandoned due to insufficient evidence.

• Morphological evidence of evolution is based on the presence of homologous, rudimentary and atavistic organs in many living organisms.

• Paleontological evidence of evolution includes fossils and imprints of ancient organisms, phylogenetic series (series of evolutionary development of an organism), and the presence of transitional forms of organisms. For example, Archaeopteryx (reptiles to birds), the hypertrophic lizard (reptiles to mammals), Latimeria (fish to amphibians), Euglena green (animals to plants).
  The richest paleontological material is one of the most convincing proofs of the evolutionary process that has been going on on our planet for more than 3 billion years. There are specific analyses that allow relatively precise determination of the age of found fossils, such as radiocarbon analysis, based on measuring the content of the radioactive isotope ¹⁴C in the material in relation to stable isotopes of carbon.

• Biogeographic Evidence for Evolution. Distribution of animals and plants on the surface of our planet, comparison of flora and fauna of different continents, islands, identification of relict plants and animals of different natural zones indicates that the distribution of living beings on the planet is closely related to the transformation of the Earth's crust and to evolutionary changes in species. Biogeography studies these patterns. For example, biogeography can explain why there are no polar bears in Antarctica and no penguins in the Arctic, even though both places have similar climates. For biogeographers, the flora and fauna of islands are of interest, which turned out to be entirely dependent on the origin history of these islands. For example, all Galapagos (Darwin) finches are birds that have a common ancestor that lived on the mainland 2-3 million years ago and then came to different islands and developed there in their own way. Each group of finches differs in size and shape of the beak as well as in the color of plumage, despite the common ancestor.

• Molecular and biological evidence for evolution. DNA and molecular data analysis makes it possible to find similarities and differences between long extinct and modern organisms. Using modern DNA analysis techniques, we can reconstruct the history of life, build a unified phylogenetic tree of all life on earth, and analyze gene changes in modern species compared to extinct ones.

Conclusion

Evolution is a very simple algorithm for creating new things. All living things reproduce, that is, they create their own copies. These copies always contain small changes. Under different conditions, some copies gain advantages over others, leave more offspring and pass on useful traits by inheritance. The adapted survive and the unadapted die. The process never stops. That is why evolution cannot have a pinnacle. All organisms alive today have passed through the filter of natural selection and been successful.

Modern theory emphasizes genetic variation and mutations. Mutational and recombinational variability provide material for natural selection. The modern theory of evolution differs from Darwin's theory because it contains more factors influencing evolution. Darwin's unit of evolution is a species, while the modern theory is a population living apart from others.

There are many different information sets that help prove the theory of evolution: embryological, morphological (comparative-anatomical or comparative-morphological), paleontological, biogeographical, and molecular-biological proofs of evolution.