In this blog post, we will explore how the theory of evolution explains biological diversity and the origin of life, focusing on natural selection and genetic variation.
In a broad sense, the theory of evolution refers to the overall body of theories regarding evolution; simply put, evolution refers to the process by which heritable traits change within biological populations. When we speak of the theory of evolution, we typically think of Darwin’s theory and its subsequent developments, but in fact, ideas about evolution have existed since ancient Greece. For example, philosophers such as Empedocles (c. 490–430 BCE) and Anaximander (c. 610–546 BCE) are considered among the first to have reflected on evolution. Thus, the concept of evolution itself existed long before Darwin.
Following the ancient Greek philosophers, a scientific approach to species and their origins did not begin in earnest until the 17th century. The precursor to modern evolutionary theory was the work of Lamarck (1744–1829), who argued that all living organisms develop into increasingly perfect and complex forms over successive generations. According to Lamarck’s theory, the simpler a living organism is today, the shorter its evolutionary history. Lamarck argued that acquired characteristics, such as muscles developed through daily life, are passed on to offspring; however, he failed to provide evidence for this claim and was subsequently criticized. As various theories, including Lamarck’s, emerged and underwent criticism, Darwin’s (1809–1882) theory of evolution—which is widely accepted today—came into being.
Darwin systematized the theory of evolution in his book *On the Origin of Species* (1859). His theory forms the foundation of modern evolutionary theory, and the main content of *On the Origin of Species* can be summarized into four key principles.
First, all species possess the ability to reproduce through self-replication. For example, while offspring can be born between lions and tigers—which are genetically closely related—these offspring are infertile and are not recognized as a new species. Therefore, self-replication is an essential prerequisite in the evolutionary process.
Second, variations occur during the replication process. Differences between individuals arise due to variations such as mutations, and these differences are often inherited. If self-replication were perfect, evolution would not occur. It is the imperfection of the self-replication process—specifically, the instability inherent in the possibility of mutation—that actually enables evolution. Traits developed through environmental factors, such as muscles, are not inherited and thus cannot serve as factors in evolution; however, mutations occurring in the genetic code (DNA) are highly likely to be inherited and can play a crucial role in evolution.
Third, competition for survival arises among individuals because resources in the environment are limited. If there were sufficient resources in the environment for all individuals to survive, both mutated and non-mutated individuals would survive, and the species would not change in any specific direction. The process by which individuals adapt to their environment occurs through competition in an environment with limited resources. When the environment reaches a state of saturation, competition within the species inevitably arises over the limited resources.
Finally, the fourth condition is that individuals with a survival advantage produce more offspring. This process is called survival of the fittest through natural selection. Individuals well-suited to the environment survive intra-species competition, increasing their opportunities to reproduce; consequently, the number of offspring carrying their genes and mutations increases. This entire process is probabilistic; individuals that gain a slight survival advantage through variation lead to an increase in individuals with favorable traits over several generations.
The core of Darwin’s argument is that through this process, populations adapt to the environment over a long period of time and undergo overall changes, and that when these changes accumulate, new species can eventually form.
Darwin’s theory of evolution later combined with Mendelian genetics to develop into Neo-Darwinism, which is now considered the established theory. August Weismann (1834–1914) refuted Lamarck’s claims—which Darwin had been unable to completely dismiss—and argued that evolution occurs solely through the process of natural selection. This theory evolved into a comprehensive modern evolutionary framework by explaining Darwin’s theory through Mendelian genetics. Its core contribution lies in enhancing the logical coherence of Darwin’s theory by establishing that traits are transmitted to the next generation through genes.
Another notable evolutionary theory is that of Richard Dawkins (1941–). His book *The Selfish Gene* has become established as the standard view in both academic and popular circles since its publication. The core of Dawkins’ theory is that genes function as the agents of the evolutionary process, going beyond the reproduction of an individual’s offspring and the transmission of information, while the individual is merely a vessel for carrying genes. While it shares the same premise as Darwin’s theory—that natural selection is the driving force of evolution—the major difference lies in the shift of the subject of evolution from the individual to the gene. Dawkins’ perspective has made it easier to understand group behaviors and altruistic behaviors that were previously difficult to explain. For example, worker bees or ants that work for the queen despite being unable to reproduce may appear irrational from the individual’s perspective. However, since they share the queen’s genes, their behavior can be explained as an effort to promote the reproduction of those genes. This interpretation—that behaviors appearing to be altruistic are actually calculated actions designed to increase the replication rate of the genes themselves—has become possible, and Dawkins’s theory of evolution is widely accepted in academic circles.
One reason why evolutionary theory, despite being a widely accepted theory, still retains a hypothetical status is the controversy surrounding creationists. Creationists and religious people have long viewed evolutionary theory as a sensitive topic, making it a subject of controversy. Some scientists argue that evolutionary theory does not provide a complete explanation for macroevolution. However, modern evolutionary theory explains that macroevolution can occur through the speciation of countless microevolutionary changes over long periods of time. In addition to this, there are several other controversies, leading to movements that reject evolutionary theory.
Evolutionary theory is a theory that explains the diversity of countless species on Earth and how organisms have changed over time. The core of evolutionary theory is that species change through the four principles previously described: self-replication, mutation, environmental constraints, and natural selection. Although evolutionary theory is sometimes opposed by or questioned by creationism, its significance lies in the fact that it explains many aspects of nature scientifically and holds the potential to explain even more in the future.
