Life has evolved through natural selection and genetic drift. Natural selection favors traits that are adapted to the environment, while genetic drift influences evolution through random changes. How do these two processes work, and what role do they play in biological diversity?
Organisms have adapted to their living environments, evolving from simple organic compounds into increasingly complex forms. In this process, organisms have not only competed for survival but have also passed on genetic traits to their offspring through reproduction, evolving into sustainable life forms. In this way, organisms have maintained their survival by adapting more flexibly to their living environments and have developed into forms that are more advantageous in the competition for survival. This is a complex process that goes beyond mere biological adaptation to include the behavior of biological populations, physiological changes, and interactions within ecosystems. It was Charles Darwin who theoretically established the concept of evolution as we generally understand it and led us to accept evolution as a fact.
Darwin’s theory of evolution presented the fundamental principles of biological evolution, and his theory laid the foundation for modern biology. Although various theories and ideas about evolution existed before Darwin, he was the first to systematically organize them and explain them based on scientific evidence. From the initial emergence of evolutionary ideas through the development of genetic research up to the present day, evolutionary theory has continued to be revised and refined. In modern times, the first person to develop ideas about evolution was Lamarck. Lamarck established a classification system ranging from minerals and plants to animals, interpreting the overall trend as evolution. He proposed the “theory of use and disuse,” which posited that organisms acquire characteristics in response to their environment and pass these on to the next generation. For example, he explained that the giraffe’s long neck was the result of frequently using its neck to eat leaves from high tree branches. However, his theory was later disproved through scientific verification.
Afterward, the person who established the theory of evolution was Charles Darwin. In his book *On the Origin of Species*, he explained the principle of how new species arise, based on competition for survival, natural selection, and diversification. Through observations of various biological species, Darwin discovered the principle of natural selection and systematically organized it. During his voyage on the Beagle, he observed finches on the Galápagos Islands and realized the importance of adaptation to the environment and natural selection. Although *On the Origin of Species* caused significant social controversy and upheaval when it was first published, over time, Darwin’s theory came to be widely accepted among scientists. By the 20th century, the field of evolutionary research had branched out in various directions. Scientists combined Darwin’s natural selection with Mendel’s genetics to advance evolutionary theory and present modern evolutionary theory.
Evolution occurs primarily through natural selection—where advantageous genetic traits are selected due to the interaction between biological populations and their environment—and through genetic drift within populations. Through natural selection, genetic traits that are advantageous for a population’s adaptation to the environment are passed on to the next generation, while disadvantageous traits are eliminated. The tendency of natural selection can be gauged through a measure called fitness, which represents the ratio of the number of offspring carrying a particular allele to the number of parents carrying that same allele. A high fitness indicates that the allele is prominent within the population, and this eventually becomes a characteristic of the species. This fitness is not fixed but continues to change as the environment changes. Natural selection does not merely affect the survival and reproduction of organisms; it also influences social structures and behavioral patterns within the population. For example, if a specific behavior promotes successful survival and reproduction within a population, the genetic trait that causes that behavior will gradually spread.
It is not merely interactions with the environment and competition for survival that influence selection. For instance, the peacock’s colorful feathers or the stag’s antlers may actually be a disadvantage for survival. Nevertheless, the reason these traits actually exhibit high fitness is related to female sexual selection during mating. Because females prefer peacocks with colorful feathers or male deer with large antlers, these traits have evolved to become even more colorful and larger. In some cases, these genetic traits develop to such an extent that they negatively impact the males’ survival. In this way, evolution arises from internal selection within a population or various factors related to the environment. It acts as a key mechanism that promotes biological diversity and provides important clues for understanding how specific traits become established within a population.
Genetic drift refers to changes in a population’s genetic composition due to random events; specifically, it describes the random fluctuation in the frequency of alleles within a population. This can be easily understood through a bead-filling experiment. Suppose there are 10 red beads and 10 blue beads in a jar. If we repeat the process of randomly drawing and replacing these 20 beads 20 times, placing the resulting beads into a new jar, we can fill the new jar with 20 beads. As this process is repeated, the new bottle may end up containing only blue marbles or only red marbles. In other words, as generations pass, the frequency of expression of a single allele continues to change randomly. Through this process of genetic drift, a particular allele becomes fixed, giving rise to a population with a new genetic trait, and this population then undergoes the process of evolution through further genetic drift. The frequencies of blood types A, B, and O are a good example; the proportions of people with these blood types continue to change randomly over generations. This genetic drift continuously provides opportunities for independent genetic traits to survive and reproduce, and it primarily occurs in small, isolated populations. While natural selection favors traits advantageous for an individual’s survival, genetic drift drives the evolutionary process randomly, regardless of whether traits are advantageous or disadvantageous for survival. In this way, living organisms adapt to their environment and evolve into new species through the evolutionary processes of natural selection and genetic drift.
Charles Darwin’s theory of evolution failed to explain how species formed as a result of natural selection come to possess genetic diversity. Darwin believed that all new characteristics appearing in species were acquired through environmental influences, and he failed to propose a theory beyond the use-and-disuse hypothesis regarding the inheritance of acquired traits as a cause of evolution. Later, as it was proven that acquired traits are not inherited, Darwin’s theory of evolution had limitations in explaining the principle by which genetic traits are passed down to the next generation. Meanwhile, as Mendel established the laws of inheritance, it became possible to explain the principle by which genetically inherited traits selected by natural selection are passed on to the next generation. This was later integrated with Charles Darwin’s theory of evolution, establishing the fundamental foundation of evolutionary theory. In the 20th century, various perspectives on evolutionary theory emerged, and a process of integrating these theories took place. From the 1920s through the 1930s, evolutionary biologists such as Ronald Fisher studied Mendel’s laws of inheritance and Darwin’s theory of evolution in greater detail, thereby pioneering the new field of population genetics, which became the foundation of modern evolutionary theory. Subsequently, with the discovery of the structure of DNA by Watson and Crick, genetics and molecular biology have also merged with evolutionary theory, becoming recognized as important fields, and research in these areas is ongoing. Thus, the modern synthetic theory of evolution is based on Charles Darwin’s theory of natural selection and integrates concepts such as mutation, Mendel’s theory of inheritance, and DNA theory. In modern evolutionary theory, evolution is explained as the changing frequency of alleles within the gene pool over successive generations, and it is an endless process of progress.
Although evolutionary theory has sparked much controversy in society since its inception, it is now widely accepted and has undergone significant development up to the present day. The impact of evolutionary theory on society goes beyond mere scientific discovery. It has influenced various fields, including philosophy, ethics, and sociology, and has presented new perspectives on human existence and life. As technology has advanced and mechanisms such as genes and DNA have been elucidated, evolutionary theory has been revised and further refined. By the 21st century, its scope has expanded beyond biochemistry and genetics to include psychology, philosophy, computer programming using evolutionary algorithms, and even artificial life, continuing to exert influence and evolve. These multifaceted studies and developments have elevated evolutionary theory beyond a mere biological theory, granting it a central role in various fields of life sciences. This signifies that evolutionary theory does not remain confined to past theories but provides a crucial foundation for future scientific and technological advancements.
