In this blog post, we’ll explore the core concepts and limitations of various evolutionary theories, with a focus on natural selection.
When we hear the term “evolutionary theory,” we often think of Darwin’s theory of human evolution from Australopithecus. As such, the theory of evolution is a topic we frequently encounter in our daily lives, yet it is also a subject that sparks much controversy. However, few people actually have a clear understanding of what the theory of evolution precisely entails. In this post, I’d like to take a step-by-step look at the assumptions underlying the theory of evolution, the theories that comprise it, and the limitations and contradictions inherent in those theories.
The theory of evolution is not merely a theory newly proposed in modern times; its ideas have existed since ancient times, and its concrete form as a theory was established in the modern and contemporary eras. Lamarck’s “theory of use and disuse” is often cited as its representative starting point. This theory posits that, depending on their living environment, the organs that organisms use frequently develop, while those they do not use degenerate, and that these acquired traits are passed on to their offspring. For example, it explains that giraffes developed long necks as a result of constantly stretching to eat leaves from tall trees, and that this trait was passed down to their descendants, giving rise to the long-necked giraffes we see today. However, as it was scientifically proven that acquired traits are not inherited, the theory of use and disuse lost its standing in the academic community and faded into history. What emerged afterward were the theories of scholars we are familiar with, including Charles Darwin, who gradually developed the more logical and scientific “modern theory of evolution.”
Modern evolutionary theory is broadly divided into two schools of thought: gradualism and punctuated equilibrium. This distinction stems from the fact that the fossil record does not form a smooth, chronological sequence, making it impossible to fully explain the continuity between biological species. Gradualism, as the name suggests, is the hypothesis that evolution occurs as organisms change very slowly, little by little, over a long period of time, and it attributes the gaps in the fossil record to “fossil incompleteness.” In contrast, punctuated equilibrium explains that evolution occurred rapidly and explosively at specific points in time, arguing that the gaps in the fossil record reflect actual phenomena rather than a lack of evidence. In other words, the punctuated equilibrium theory posits that the evolution of organisms remains stagnant under normal conditions but changes rapidly following a specific trigger.
So, what drives evolution? Generally, four driving forces of evolution are proposed: mutation, migration, genetic drift, and natural selection. For these factors to serve as the primary mechanisms of evolution, they must go through four stages: the replication of genetic information, the occurrence of variation, competition among individuals, and natural selection. Let’s examine the validity of each theory based on these conditions.
First, the “mutation theory” explains that genetic variations occurring randomly within a population alter gene frequencies, and these variations are subject to natural selection, thereby driving evolution. However, in real-world environments, individuals with mutations often struggle to win the competition for survival; thus, this hypothesis can serve as a basis for evolution only under very limited circumstances. Next, the “migration theory” posits that evolution occurs as the genetic composition of a population changes due to the influx of individuals from external populations. However, this theory can only explain the simple phenomenon of individual movement; since it makes no mention of variation or competition, its explanatory power is limited.
The “genetic drift hypothesis” focuses specifically on the phenomenon where, particularly in small populations, certain traits disappear by chance. For example, if a colony of 60 ants originally included 20 large ants, and all of them were lost due to external factors, the entire population would consist of relatively small ants, and as a result, “small size” could become fixed as a genetic trait. However, this hypothesis is also difficult to apply to large populations or long-term evolutionary phenomena. In this regard, most scholars recognize the mechanism of natural selection as the primary driving force of evolution, as it can explain evolution relatively comprehensively under a wide range of conditions.
Theories of evolution based on the mechanism of natural selection can be broadly divided into Darwin’s theory of evolution and Dawkins’ theory of evolution. Both theories share the following common premises as basic conditions for evolution to occur: that more offspring are born than can survive; that individuals within the same species possess different traits; that individuals with traits suited to the environment have an advantage in survival and reproduction; and that these traits can be passed on to offspring. The mechanism of natural selection explains the process by which evolution occurs: when these four conditions are met, competition arises among individuals, and the traits of those that survive this competition are passed on to subsequent generations.
However, the two theories differ in their views on the unit at which evolution occurs. While Darwin viewed evolution as occurring at the “individual” level, Dawkins argued that it occurs at the “gene” level. According to Darwin’s argument, one could explain the evolution of beak length by comparing birds with different beaks. However, this risks falling into a logical fallacy similar to treating a “long chalk” and a “short chalk” as two entirely different individuals and claiming that one of them gradually became shorter. In other words, Darwin’s theory faces criticism for having limitations because, to explain evolution, one must demonstrate that a single, identical individual or unit has gradually changed over time; yet, comparing only different individuals does not clearly identify the agent of that change. Furthermore, Darwin’s theory failed to provide convincing evidence for why individuals engage in altruistic behavior—that is, how to explain cooperation and self-sacrifice. This is because, if natural selection is a process that maximizes “self-survival,” cooperation is an irrational behavior.
In contrast, Dawkins sought to resolve these issues by identifying the “gene” as the agent of evolution. If evolution occurs at the genetic level, genes undergo gradual changes as they are passed on to offspring, which in turn can alter an individual’s traits. Since both mutated and unaltered traits are preserved, a “baseline for change” exists, ensuring logical consistency. Furthermore, Dawkins explained cooperation and altruism as survival strategies of genes. In other words, individuals cooperate to increase the survival chances of those carrying the same genes as themselves, thereby ensuring that those genes are passed on to the next generation in greater numbers. This explanation has been of great help in understanding the behavioral patterns of social animals.
Nevertheless, Dawkins’ “selfish gene” theory is also the subject of much controversy. Although Dawkins argued that “we are merely survival machines and carriers of genes,” the interpretation that higher-order thoughts and emotions—such as human language ability or moral behavior—are also strategies of genes is difficult for many people to accept. For example, the behavior of bats sharing blood with unrelated bats cannot be fully explained solely as a survival strategy of genes.
As such, defining and explaining evolutionary theory is no simple task. Since evolutionary theory is a hypothesis, it has not yet been fully established, and even its basic premises are subject to diverse disagreements among scholars. For example, while there is general agreement that natural selection is the core driving force of evolution, some scholars question even this. Furthermore, the debate over what constitutes the basic unit of natural selection continues to this day. While most scholars view genes as the basic unit of evolution, Edward Wilson and David Wilson advocate for multilevel selection, arguing that populations—rather than genes—can serve as the unit of evolution. In addition, theories such as kin selection add further perspectives to this debate, which continues to be actively discussed today.
Therefore, while it is difficult to clearly define evolution in a single sentence, based on what we have examined so far, it can be summarized as the phenomenon in which individuals or their internal traits gradually change through the mechanism of “natural selection.” Darwin argued that this evolution occurs at the “individual” level, while Dawkins argued that it occurs at the “gene” level.
The theory of evolution is not merely a biological theory; it has influenced various academic disciplines and society as a whole. For example, by misapplying the logic that humans also compete between races according to the principle of natural selection, the Nazis labeled Jews and other ethnic groups as inferior and carried out mass murder. Furthermore, the theory of evolution was used to justify the genocide and oppression of indigenous peoples by white settlers. In education, it laid the foundation for a culture that emphasizes wisdom and learning, based on the premise that humans overcome the competition for survival through knowledge. Religiously, while it initially made it possible to argue that “God endowed humans with the ability to evolve,” it later raised questions that led to demands for scientific evidence of God’s existence. Evolutionary theory has also had a significant practical impact: the genetic algorithm proposed by American computer scientist John Henry Holland is used to enable computer programs to “evolve” much like living organisms, and it plays a crucial role in the development of artificial intelligence and optimization technologies today.
As such, the theory of evolution is not merely an academic hypothesis but a powerful intellectual framework that has exerted a tangible influence across various fields. How the theory of evolution will develop in the future, and how we will understand and apply it, will remain an intriguing and important challenge.
