In this blog post, we will explore the overall concept of the theory of evolution, focusing on its origins, major theories and evidence, and the development of modern evolutionary biology.
Many religions have existed throughout history. Although each religion has its own distinct doctrines and principles, they share a common foundation: the creationist notion that the world was created by a deity. Meanwhile, the scientific community has long studied the theory of evolution, which explains the origin of life from a perspective different from that of creationism. While the theory of evolution does not completely contradict creationism in every respect, scholars studying evolution have engaged in prolonged debates with creationists ever since the theory emerged. Amid these debates, evolutionary biologists have continued to refine and supplement the theory through persistent research and observation. Even today, the debate surrounding the theory of evolution and creationism has not completely ended, and perspectives such as theistic evolution—which seeks to reconcile religious faith with the theory of evolution—also exist. The evolution of life has been a topic of great global interest from the past to the present, and whether one supports the theory of evolution or not, it is necessary to understand its general principles. Therefore, this section will focus on explaining the concepts and developmental history of the theory of evolution.
First, it is necessary to accurately understand the definition of the theory of evolution. Evolution refers to the natural phenomenon in which a population of organisms accumulates genetic changes over multiple generations, leading to changes in the population’s characteristics and, in the long term, the formation of new species. The theory of evolution is a scientific theory that explains this evolutionary phenomenon; it was systematized by Charles Darwin with a focus on natural selection and has since evolved into modern evolutionary biology, which integrates research from various fields such as genetics, molecular biology, ecology, and paleontology. This theory explains that today’s biological diversity was formed through the evolutionary process from a common ancestor.
Although Charles Darwin laid the foundation for modern evolutionary theory, ideas about evolution existed long before him. In the modern era, evolutionary thought began to emerge in earnest in the mid-18th century as understanding of biology deepened. At that time, scientists in France and elsewhere in Europe proposed in their writings the idea that organisms could change, and this became the starting point for evolutionary theory. In the late 18th century, Lamarck—who was influenced by the ideas of Charles Darwin’s grandfather, Erasmus Darwin—was the first to propose a relatively systematic theory of evolution.
To explain biological diversity, Lamarck proposed the theory of the inheritance of acquired characteristics and the theory of use and disuse. In other words, he explained that frequently used organs develop while unused ones degenerate, and that these changes are passed on to the next generation. Although these hypotheses are no longer accepted as general principles of evolution due to advances in modern genetics, they are of great significance in that they laid an important foundation for the subsequent development of evolutionary theory by presenting the perspective that changes in organisms occur through interaction with the natural environment.
About 20 years later, Charles Darwin sailed aboard the HMS Beagle to various regions around the world, observing a wide variety of organisms. During his expedition, he wondered why the fossils found in South America resembled the organisms currently inhabiting that region. He also collected various species of finches while observing unique organisms on the Galápagos Islands. Darwin noted that the shape of the beak differed among finch species and that these differences were the result of adaptation to the food sources and environments utilized by each population. This led him to reflect deeply on the adaptation and diversification of organisms.
After years of research, Darwin published ‘On the Origin of Species’ in 1859, centering on the concept of natural selection. Citing various biological examples, he explained that as organisms adapt to their environment, favorable traits are passed on to their offspring more frequently, and that evolution occurs through the repetition of this process. This book played a decisive role in spreading the theory of evolution and had a significant impact on the development of modern biology.
However, from today’s perspective, Darwin’s theory of evolution at that time was not yet a complete theory. Darwin partially incorporated some of Lamarck’s ideas, and, most importantly, while he explained the principle that advantageous traits are selected through natural selection, he was unable to clearly explain how such traits are inherited given the scientific understanding of the time. Subsequently, Neo-Darwinism—which placed greater emphasis on natural selection—and Neo-Lamarckism—which sought to partially acknowledge the inheritance of acquired characteristics—emerged, while Romanes and Wagner proposed the isolationist theory, arguing that geographic and reproductive isolation play important roles in evolution. With the emergence of these diverse theories, evolutionary theory began to develop in various directions.
In 1900, the rediscovery of Mendel’s laws of inheritance—which had been overlooked for some time—marked a new turning point for evolutionary theory. The combination of Mendel’s genetics and Darwin’s theory of natural selection established the basic framework of modern evolutionary theory: genetic variation accumulates through natural selection, and traits adapted to the environment are passed on to the next generation, thereby driving evolution. Subsequently, as various research findings in genetics and biology—including Hugo de Vries’s research on mutations—accumulated, our understanding of the causes and processes of evolution deepened further.
Thus, the Modern Synthesis was established, providing an integrated explanation of various mechanisms such as natural selection, mutation, genetic recombination, genetic drift, isolation, and speciation. Following World War II, the rapid advancement of molecular biology led to the discovery of the structure of DNA and the full-scale study of genes. As research in fields such as genomic analysis and molecular systematics progressed, evolutionary theory evolved into an even more sophisticated scientific theory. Even today, evolutionary biology continues to be revised and refined as it incorporates new evidence and research findings.
While studying finches on the Galápagos Islands, Darwin came across a work on population theory written by the British economist Thomas Malthus. Malthus argued that phenomena such as disease, famine, and war occur because the rate of population growth exceeds the rate of increase in food and resources. Darwin applied this discussion of society and population to the natural world. Since natural resources are limited, he reasoned that if more offspring are born than the natural environment can support, fierce competition for survival would eventually arise among the individuals, and only a few would survive in the process. He believed that differences in reproductive success among individuals arise during this process, and that this is the core principle of natural selection.
Alongside natural selection, Darwin proposed sexual selection as another important mechanism of evolution. He explained that because females often invest more energy in pregnancy and nurturing, they tend to be more selective when choosing mates, and that this selection drives the evolution of specific traits over generations. Given the social climate of the time, this was a remarkably novel perspective, and sexual selection has since established itself as one of the key principles of modern evolutionary biology.
More recently, the Handicap Principle has been proposed to explain phenomena in nature that are difficult to account for through survival of the fittest alone. A prime example is the male peacock’s magnificent tail. A peacock’s long tail is actually a disadvantage for survival, except for its role in attracting mates. Because it is heavy and conspicuous, it increases the risk of attack by predators. Nevertheless, male peacocks have evolved over a long period of time to develop increasingly elaborate tails.
At first glance, this trait appears to contradict the principles of natural selection. However, handicap theory explains that these very disadvantages can serve as signals indicating an individual’s superiority. In other words, the fact that an individual can survive despite possessing traits that are disadvantageous for survival implies that it is a healthy and genetically superior individual, and females have evolved to prefer such signals. Therefore, the colorful tail is understood not as a mere ornament but as a reliable signal indicating superior genetic potential.
The theory of evolution has developed through a long process in which numerous hypotheses have been proposed, revised, or discarded. Despite the many questions, contradictions, and various criticisms—including those from creationism—raised during this process, the theory of evolution has established itself as a core theory of modern biology because of the abundance of scientific evidence supporting it.
One of the most representative pieces of evidence is fossils. Various fossils had been discovered even before Darwin’s theory of evolution was published, and analysis of these fossils confirms that living organisms have changed over time. Today, with the advancement of various dating techniques, including radiometric dating, it has become possible to estimate the age of fossils with greater accuracy. Fossils reveal the forms and characteristics of organisms that existed in different eras, supporting the fact that living organisms have changed over long periods of time.
A prime example is the evolution of whales. While modern whales are fully marine mammals, fossils of early cetaceans—such as Pakicetus—and various intermediate-stage fossils discovered later demonstrate that they gradually adapted to an aquatic lifestyle from their terrestrial mammalian ancestors, evolving into their present form. These fossils serve as crucial evidence for understanding the evolutionary process through the structure of their forelimbs and hindlimbs, as well as changes in their skeletons.
In addition to fossils, biogeography also provides important evidence for evolution. Darwin noted that the birds of the Galápagos Islands were more similar to those of South America than to birds from other continents. He explained that the Galápagos fauna had migrated from a common ancestor in South America and subsequently diversified as they adapted to different environments.
Furthermore, comparative anatomy is one of the strongest pieces of evidence supporting the theory of evolution. Although the human arm, the cat’s forelimb, the whale’s fin, and the bat’s wing serve different functions, their basic bone structures are very similar. These homologous structures are recognized as prime examples demonstrating that different organisms evolved from a common ancestor.
Research in embryology also provides important evidence. Comparing the early embryos of different vertebrates reveals common features that are difficult to identify in adults. These similarities in developmental processes are also used as evidence that organisms evolved from a common ancestor.
In modern times, advances in molecular biology have led to active research comparing DNA and gene sequences. When comparing the gene sequences of different organisms, the closer the species, the higher the similarity; this allows for a more precise confirmation that organisms have diverged from a common ancestor. In this way, research findings from various fields—including paleontology, biogeography, comparative anatomy, embryology, and molecular biology—complement one another and strongly support modern evolutionary theory.
Although the theory of evolution has developed over a long period based on a vast amount of evidence, various views have been put forward within the scientific community regarding how to understand the specific evolutionary processes and their rates. Among these, the most prominent debate concerns the rate at which evolution occurs. Fossils, which are key evidence for evolutionary theory, demonstrate changes in living organisms; however, fossils from every era and every organism are not perfectly preserved. Consequently, scientists have had to interpret the pace and patterns of evolution based on limited fossil data, and in this process, different theories have emerged.
In the early days, the theory of gradualism—which posits that evolution occurs through the gradual accumulation of small changes over a very long period—was widely accepted. According to gradualism, organisms diverge into new species as small changes accumulate over long periods of time. However, this perspective faced criticism because there were not enough fossils of the intermediate stages of transition from one species to another—commonly referred to as “missing links.” For this reason, some argued that gradualism alone could not fully explain the fossil record.
To address this issue, the theory of Punctuated Equilibrium was proposed in the 1970s. This theory explains that evolution does not always proceed at a constant rate; rather, it maintains a stable state without major changes for most of the time, followed by periods of rapid speciation over relatively short intervals. Therefore, it suggests that few intermediate fossils may remain from periods of rapid evolution, which could explain the gaps in the fossil record.
However, this line of argument did not completely refute the theory of gradualism. Some evolutionary biologists, including Richard Dawkins, argued that the absence of “missing links” alone was not sufficient reason to reject gradualism. In fact, since fossils are formed and preserved only under very specific conditions, the failure to discover all intermediate stages does not mean that evolution itself can be denied.
The following analogy is often used to illustrate this idea. Suppose a new employee’s time records show entries only at 1:00 p.m. and 2:00 p.m. It would not be reasonable for a supervisor, upon seeing this, to conclude that the new employee was absent without leave simply because there are no records for the time between 1:00 p.m. and 2:00 p.m. Even if additional records for 1:20 p.m. and 1:40 p.m. were presented, the supervisor might continue to harbor doubts because there are still no records for the time in between. In other words, the mere fact that some records are missing does not allow us to determine whether an event actually occurred. Similarly, we cannot conclude that evolution did not occur simply because the fossil record is incomplete. This is because fossils are not records of every moment an organism existed, but rather materials that were preserved by chance in very limited environments.
In modern evolutionary biology, rather than viewing gradualism and punctuated equilibrium as completely opposing theories, there is a strong tendency to understand them as complementary explanations that can manifest in different ways depending on the type of organism and the environment. In some organisms, gradual changes may accumulate over long periods of time, while in others, rapid speciation may occur over a relatively short period due to environmental changes or the isolation of populations. Therefore, modern evolutionary biology integrates these two perspectives to explain various patterns of evolution.
Even today, there are people who misunderstand evolutionary theory and make claims such as, “According to evolutionary theory, survival of the fittest applies, so there is no need to protect the socially vulnerable.” However, such claims are examples of the misapplication of modern evolutionary biology to society. Evolutionary theory is merely a scientific theory that explains how organisms have changed in nature; it is not a theory that dictates what ethics or values human society should uphold. Therefore, using evolutionary theory to justify social discrimination or inequality amounts to confusing scientific facts with ethical judgments.
Scholars studying evolutionary theory are continuously conducting research to correct various misunderstandings about modern evolutionary theory, and they repeatedly review and revise existing theories whenever new evidence is discovered. Furthermore, they are refining evolutionary theory by striving to resolve the various questions and differences of opinion raised within the academic community through scientific verification.
Evolutionary theory is a core theory of modern biology that explains the process by which life came to possess the diversity we see today. Starting with Darwin’s theory of natural selection, it has evolved into modern evolutionary biology through the proposal, revision, rejection, and integration of numerous hypotheses. It has established itself as an even more robust scientific theory based on research findings from various academic fields, including genetics, molecular biology, developmental biology, ecology, and paleontology.
Furthermore, evolutionary theory provides crucial insights into the relationships among living organisms and the common ancestry of all life forms, including humans, and is widely applied in various fields such as the formation of biodiversity, the evolution of diseases, changes in ecosystems, new drug development, and genomic research. Going forward, alongside advancements in various scientific and technological fields—such as the discovery of new fossils, genomic analysis techniques, and biological research utilizing artificial intelligence—the theory of evolution will continue to be refined and developed, and it is expected to continue playing a vital role as a core theory for understanding the history of life.
