The theory of evolution, which explains how living things evolve, has evolved from Lamarck’s theory of speciation to Darwin’s theory of natural selection. In modern evolutionary theory, changes in the gene pool within a population are described as the essence of evolution, and natural selection, mutation, gene flow, and genetic drift are the main factors. Evolutionary theory has influenced not only biology, but also society, ethics, and politics, leading to various theories such as social Darwinism.
Why do we live? Where did we come from? We’ve all asked ourselves these questions at one point or another. These questions seem so simple, but at the same time, they’re so difficult that many ancient philosophers and theologians struggled with them. During the Middle Ages, theology was dominant, and people tried to answer this question through the belief that God created everything, including people, and that all species, once created, are unchanging forever. In other words, they set up a transcendent being called the Creator and delegated the solution of complex problems to him. However, as the Renaissance progressed through the 17th century, attempts to explain and understand all natural phenomena in terms of common laws gradually increased. People began to observe the living world around them and question the notion that life is eternally unchanging. The theory of evolution was born out of these ideas. In this article, we’ll explain how evolutionary theory 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. In his Zoology (1794-1796), Erasmus Darwin argued 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 could eat the leaves it could reach, but it kept stretching its neck to reach the leaves higher up. As it did so, its neck gradually lengthened, and this trait was passed on to its offspring. This process repeated itself, resulting in the long necks of giraffes today. However, this hypothesis lost strength when it was discovered that acquired traits are not inherited by genes in germ cells.
The next theory to emerge was Darwin’s theory of natural selection. First published in 1859 in The Origin of Species, Darwin’s theory of natural selection states that evolution occurs through the process of ‘individual variation → competition for survival → natural selection’. Using giraffes as an example, the theory of Darwinism assumes that tall giraffes gradually grew taller, while the theory of natural selection assumes that tall and short giraffes coexisted from the beginning. The taller giraffe was able to eat higher leaves, which gave it an advantage in survival, and as a result, the taller giraffe was selected for, and this trait was passed on to its offspring, leading to the evolution of taller giraffes. Darwin’s concepts of individual variation, competition for survival, and natural selection are among the most important foundations of modern evolutionary theory and have been widely applied in the social sciences and beyond.
However, an unresolved question in Darwin’s theory was how traits are passed on to offspring. At the time, the theory of mixed inheritance prevailed, which suggested that offspring would inherit half the traits of their parents. However, this theory was inconsistent with Darwin’s theory of natural selection, which states that the characteristics of organisms change slightly over time, because even if certain traits are passed on to offspring, they are diluted during interbreeding. To solve this problem, Darwin proposed the pangenesis hypothesis. According to this hypothesis, every cell of an organism contains a gemmule, a self-proliferating particle, which is released during reproduction and transmits traits to the offspring. However, this theory also became unconvincing because acquired traits are not inherited.
It was Mendel’s theory of genetics in 1865 that completely refuted the mixed inheritance theory. Through his pea experiments, Mendel proposed that an individual has two genetic factors that determine a particular trait, one inherited from each parent. If the alleles are different, only the dominant allele is expressed, and these alleles separate during gamete formation, enter different gametes, and pair up again during fertilization. Later, Weismann drew a clear distinction between germ cells and somatic cells, showing that inheritance occurs only through germ cells and proposing the germline continuum. Eventually, in 1953, the structure of DNA, the genetic material, was discovered by Watson and Crick, clarifying the process by which traits are transmitted to offspring.
De Vries proposed the theory of mutation through his experiments with evening primroses, explaining how individual variation appears in Darwin’s theory. Wagner and Romanes also argued that evolution occurs through isolation. The 20th century saw the introduction of population genetics by Hardy, Weinberg, S. Wright, Fischer, and Holdane, which analyzes evolution through changes in the frequency of certain alleles in a population rather than changes in individual traits.
Modern evolutionary theory explains that individuals in a population are isolated in different environments, and then various variants emerge through mutations and hybridization in reproductive cells, and individuals with these variants are reproductively isolated and differentiated into different species through natural selection. Population genetics, especially as developed by Hardy, Weinberg, S. Wright, Fisher, and Holdane, introduced the concept of “gene pools,” or populations rather than individuals, as the object of study in evolution. A gene pool is the set of alleles possessed by individuals in a population at a given time, and changes in the frequency of alleles in the gene pool are interpreted as evolution. Four factors have been 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 follows Darwin’s theory of evolution, while genetic drift refers to the rapid change in the frequency of certain alleles due to chance events such as forest fires. Finally, genetic drift is the introduction of new alleles, such as migration of individuals from neighboring populations, that cause changes in frequency.
New theories of evolution are constantly emerging and existing theories are being re-evaluated. For example, Lamarck’s theory of the insoluble dragon has been revisited, as it has been suggested that acquired traits can be inherited through the process of DNA methylation. Research suggests that exercise alters the unique DNA methylation patterns within tissue cells, and that these changes can be passed on to offspring. While this is still controversial, it shows that evolution is a living theory, with new views emerging all the time.
In addition, evolutionary theory has also had a major impact on other disciplines, changing the way people value life. In the 19th century, Herbert Spencer introduced social Darwinism. He argued that human life is also subject to competition and natural selection, justifying the survival of the fittest. The result was a dehumanized society where racism was justified over equality and welfare. Some even used it in imperialist policies to justify colonization. In addition to changing perceptions of the nature of human society, evolutionary theory has also had a significant impact on ethical values and policies.
