How did evolutionary theory develop and how has it influenced modern biology?

The theory of evolution has evolved from Lamarck’s theory of solubility, through Darwin’s theory of natural selection, Mendel’s genetics, and modern population genetics. The theory not only explains changes in living things, but it has been applied to a wide range of disciplines and has profoundly changed social and scientific thinking.

 

Why do we live? Where did we come from? We’ve all asked ourselves this question at one point or another. These questions are so simple, yet so difficult at the same time, that they puzzled countless ancient philosophers and theologians. During the Middle Ages, theology prevailed, and people sought an answer to this question through the belief that a creator created everything, including people, and that all species were created once and remain unchanged forever. By setting up a transcendent being called the Creator, they delegated the solution of complex problems to him. However, during the Renaissance and into the 17th century, there were increasing attempts to explain and understand all natural phenomena through common laws. As they observed the living things around them, they began to question the idea that they were unchanging forever. The theory of evolution gradually developed from these ideas. In the following, we’ll explain how evolutionary theory specifically developed, how modern evolutionary theory explains how living things change, and how it has been used in other fields.
Lamarck’s Theory of the Origin of Species was the first to express the idea that living things change in the form of a systematic theory. Erasmus Darwin wrote in Zoology (1794-1796) that “all warm-blooded animals possess the power of modifying parts of themselves, and that these improved traits are transmitted to their offspring.” Lamarck influenced this idea. Lamarck was influenced by this idea, and in his 1809 Philosophical Zoology, he argued that creatures adapt to their environment while they are alive, and the traits they acquire are passed on to the next generation. For example, there was a short giraffe that was able to eat leaves within its reach, but it was hungry and wanted to eat leaves higher up, so it kept lengthening its neck, and the slightly longer neck was passed on to its offspring. This process repeated itself, and the giraffe’s neck became as long as it is today. However, when it was realized that the mediators of trait transmission are genes in the germ cells, it was confirmed that acquired traits are not inherited.
The next theory to emerge was Darwin’s theory of natural selection. Published in 1859 in The Origin of Species, Darwin’s theory states that evolution occurs through the process of ‘individual variation → competition for survival → natural selection’. To continue with the giraffe example, while the theory of abiogenesis explains that giraffes that were short became taller and taller, the theory of natural selection explains that there were originally a variety of tall and short giraffes. However, the taller giraffes had an advantage in survival because they could eat the leaves at higher elevations, and as a result, the taller giraffes were selected for and this trait was passed on to their offspring, resulting in the evolution of taller giraffes. Darwin’s concepts of individual variation, competition for survival, and natural selection have provided the most important theoretical foundations of modern evolutionary theory and have been widely applied in other fields, including the social sciences.
However, a major unresolved question was how traits are passed on to offspring. At the time of Darwin, the theory of mixed inheritance prevailed, which suggested that offspring would have half the characteristics of their parents. However, if this theory was correct, it would discredit Darwin’s theory of natural selection, which states that the characteristics of organisms change slightly over time, because even if certain traits were passed on to offspring, they would be diluted in the process of interbreeding. Furthermore, Darwin’s own experiments with crosses often showed that the offspring exhibited only some of the traits of the parents rather than a mixture of them. Eventually, Darwin became suspicious of the mixed heredity theory and proposed the pangenesis hypothesis. The idea is that every cell in an individual contains a gemmule, a very small, self-proliferating particle, which is shed during reproduction, passing on traits to the offspring. However, Darwin’s theory was undermined when it was discovered that acquired traits were not passed on to the offspring, as was the case with the Dragon’s Den.
The theory that completely refuted mixed inheritance was Mendel’s theory of genetics, published in 1865. Mendel, who was strongly suspicious of mixed inheritance after the pea experiment, proposed the theory that an individual has two genetic factors that determine a particular trait, one inherited from each parent. If the alleles are different, he argued, only the dominant allele is expressed, and these alleles are separated during gamete formation, entering different gametes, and then re-paired by fertilization. Weismann proposed the germline continuation theory by clearly distinguishing between germ cells and somatic cells, showing that inheritance is carried out only by germ cells, and finally, in 1953, the structure of DNA, the genetic material, was revealed by Watson and Crick, clarifying the process of transmitting traits to offspring.
De Vries proposed the mutation theory through his experiments with evening primroses, explaining how individual variation appears in Darwin’s theory, and Wagner and Romanes argued that evolution occurs through isolation. In the 1900s, Hardy, Weinberg, S. Wright, Fischer, and Holdane introduced population genetics, which identifies evolution through changes in the frequency of certain alleles in a population rather than changes in traits in individuals, and modern evolutionary theory was completed.
The modern theory of evolution states that individuals in a population are isolated in different environments and then develop multiple variants through mutations and hybridization in their reproductive cells, and that individuals with these variants are reproductively isolated and differentiated into different species in the process of natural selection. Population genetics, especially developed by Hardy, Weinberg, S. Wright, Fisher, and Holdane, has led to the concept of “gene pools,” where the object of evolutionary study is not an individual but a population (a group of individuals). A gene pool is the set of alleles carried by individuals in a population at a given time, and evolution occurs when the frequency of alleles in the gene pool changes. Four factors are proposed to cause gene pools to change: mutation, natural selection, genetic drift, and gene flow. Mutation, borrowed from de Vries’s theory, is a change in genetic material that results in the appearance of a new trait. Natural selection, borrowed from Darwin’s theory of natural selection, is the survival of the best-adapted individuals in an environment. Genetic drift is when the frequency of a particular allele changes rapidly due to chance events. An example is the death of a herd of deer in a forest fire. Genetic drift is a change in frequency due to the introduction of new alleles, such as when individuals from neighboring populations migrate.
New theories of evolution are constantly emerging and existing theories are being re-evaluated. For example, Lamarck’s theory of the insoluble dragon has recently been revisited, as it has been suggested that acquired traits can be inherited through a process called DNA methylation. Research has shown that exercise alters the unique DNA methylation patterns of tissue cells. This means that the changes you make can be passed on to your offspring. Of course, this is still controversial, but it shows that evolutionary theory is still a work in progress, with new ideas emerging all the time.
In addition, evolutionary theory has influenced many other disciplines by changing the way people view the world. In the 19th century, Herbert Spencer introduced social Darwinism. The theory justified the survival of the fittest rather than equality because there is competition and natural selection in human life. As a result, a dehumanized society was created in which equality and welfare were pushed aside and racism was justified. It has also led to the idea that poor people, or non-white people, must be eliminated in order for humanity to move forward in a better direction. This was the result of misinterpreting “evolution” as “progress” and overinterpreting evolutionary theory. Evolutionary theory has a sad history of being used to justify aggression and oppression.
In the 20th century, Wilson opened a new field of study called sociobiology, which explains human social behavior through evolutionary principles. His explanation of altruism, reciprocal behavior, and other behaviors that seemed too vague to be analyzed in terms of evolutionary principles had a great impact, and since then, attempts to explain human culture in biological terms have appeared in various disciplines.
The theory of evolution was such a major event that it changed the framework of human thinking that there is no discipline that has not been affected. As such, the theory was framed and developed by numerous scientists in the 18th and 20th centuries, from Lamarck to Hardy to Weinberg, and continues to be studied today.