In this blog post, we will examine whether the theory of evolution simply explains changes in living organisms, or if it can also encompass the evolution of culture and language.
People often encounter the word “evolution” in broadcast media, comics, and movies, but many do not actually know exactly what evolution is. Biological evolution refers to the phenomenon of organisms changing over time, and the theory that explains this is evolutionary theory. Evolutionary theory has long been established as a core theory in biology, and its importance is growing as it now influences not only other scientific fields but also various disciplines such as the humanities and philosophy. In this article, we will examine the core concepts and development of evolutionary theory, as well as its impact on other fields.
According to the biological definition, evolution refers to “the phenomenon in which the frequency and proportion of genes change within a population over generations.” Countless pieces of evidence confirm the existence of evolutionary phenomena, such as observing how organisms have changed over time through the dating of fossils, or analyzing how species sharing a common ancestor have evolved into different forms in different environments. However, research into the causes and mechanisms of evolution is still ongoing, and among these, the most widely accepted mechanisms are natural selection and genetic drift.
Natural selection refers to the phenomenon in which individuals possessing traits better suited to a specific environment gain an advantage in survival and reproduction over those without such traits, leading to those traits gradually becoming dominant within the population. For natural selection to occur, the reproductive process through which genes are passed on to offspring is essential, and a trigger for the emergence of new traits is also necessary. Changes in genes caused primarily by mutations serve as such triggers. While mutations are generally disadvantageous to individuals, if advantageous mutations occur over generations, individuals possessing those traits will produce more offspring through natural selection. Through this process, individuals well-adapted to the environment survive and influence the next generation.
The patterns of natural selection within a population can be broadly divided into three categories. The first is directional selection, which occurs when evolutionary pressure is exerted in a single direction by the external environment. The second is divergent selection, an evolutionary process in which opposing traits gradually become polarized. The third is stabilizing selection, which refers to an evolutionary pattern in which intermediate traits within a population become dominant, while extreme traits decline. African cichlids are a prime example of directional selection; studies analyzing their diverse oral structures and feeding behaviors have reportedly confirmed the influence of directional selection.
Darwin and other early evolutionary theorists believed that trait selection primarily occurred during the mating process. Generally, because females invest more energy in reproduction and parenting than males, the phenomenon of “sexual selection”—in which females select males—occurs. Although the concept of sexual selection—which initially emerged to explain the advantages of sexual reproduction over asexual reproduction—was long ignored due to its association with women’s rights, various studies have been conducted in modern times. A prime example is the “Red Queen Hypothesis,” which explains that the diversity of sexual reproduction provides an advantage for adapting to changing environments and surviving against competitors such as parasites. This hypothesis describes a scenario where both parasites and hosts face evolutionary pressures due to mutual competition: parasites find it increasingly difficult to adapt to the host’s genetic diversity, while the host, in turn, faces evolutionary pressures to respond to this. Another theory, the “handicap hypothesis,” explains why males possess traits that are unnecessary for survival.
For example, it explains that while a peacock’s colorful tail or a stag’s large antlers do not aid survival, females perceive these as evidence of survival ability and health, leading to selection and evolution toward the fixation of such handicaps. However, despite these explanations, theoretical limitations have been pointed out, such as the fact that the purpose of mating is not limited to reproduction alone and that it is difficult to explain homosexuality.
Another major mechanism of evolution, genetic drift, refers to the phenomenon where the frequency of alleles changes over generations. In sexual reproduction, since parents’ genes are randomly combined and passed on to offspring, even children of the same parents can possess different traits. If not influenced by the environment, this tends to accumulate, much like sampling error in statistics. However, when a specific trait is selected in a particular environment, the frequency of traits advantageous for survival increases, while that of disadvantageous traits decreases. If this process repeats, genetic traits may gradually become fixed or disappear. This process occurs even more rapidly in small populations, a phenomenon known as the “genetic bottleneck.” The bottleneck effect can reduce genetic diversity among individuals, potentially threatening the survival of the species.
The “neutral theory of evolution” regards genetic drift as a major factor in evolution. According to this theory, most mutations do not directly affect biological functions and are therefore not subject to selection; since approximately 90% of human DNA consists of nucleotide sequences unrelated to biological functions, the majority of mutations are neutral. This differs from natural selection, where specific variants are selected; instead, it explains that neutral variants generate new alleles, which become fixed through genetic drift, thereby driving evolution. Modern evolutionary biologists view both genetic drift and natural selection as important factors in evolution.
Although evolutionary theory has developed over a long period across various fields and accumulated substantial evidence, gaps in the evolutionary record remain. These “missing links” arise because not all fossils can be preserved; just as one can infer the whole picture even when some pieces of a jigsaw puzzle are missing, evolutionary theory can explain the overall phenomenon despite the absence of some evidence. Early evolutionists advocated for gradual evolution, arguing that specific genetic traits accumulated gradually over time, leading to change. However, this theory was criticized because the slow pace of evolution meant that fossils of intermediate forms were scarce.
Punctuated equilibrium, which emerged in the 1970s, argues that evolution often occurs rapidly over short periods, with little change during the intervening periods. According to the punctuated equilibrium theory, the reason missing links have not been discovered may be that evolution occurs intermittently, leaving gaps in the evidence for specific periods. Richard Dawkins suggested the possibility of coexistence between the two theories, arguing that the pace of evolution is explained from different perspectives depending on the theory, and that while changes at the genetic level are gradual, phenotypic changes can occur abruptly.
Today, as life science research and analytical technologies advance, evolutionary research is also becoming more active. Scientists have discovered “horizontal gene transfer,” a phenomenon in which genes are directly transferred between individuals or species without going through reproduction. This phenomenon occurs not only in microorganisms but also in plants and animals. A prime example is that chloroplasts in plant cells and mitochondria in animal cells—cellular organelles with their own DNA and double-membrane structures—are believed to have come to exist within cells through horizontal gene transfer. This discovery further broadens the possibilities of evolution.
Epigenetics is also proposing new evolutionary mechanisms. Epigenetics argues that the environment can influence gene expression, which partially accepts Lamarck’s theory of use and disuse—the idea that acquired traits can be inherited. In the case of the nematode Caenorhabditis elegans, there are instances where the environmental history of ancestors has been passed on to descendants, and epigenetic phenomena have also been confirmed in higher organisms.
Evolutionary theory is not limited to biology but influences various fields. The theory that culture and language evolve is frequently discussed in academia, and memes, in particular, are gaining attention as elements of cultural evolution. Linda Focus studied language from an evolutionary perspective, and recently, social structures, economics, politics, and even religious phenomena have begun to be interpreted from an evolutionary standpoint. Although biological evolution and cultural evolution differ significantly, attempts to understand society through the basic concepts of evolutionary theory demonstrate the extent of its influence.
