In this blog post, we will explore how the theory of evolution explains the origin and change of various biological species through natural selection and genetic variation.
Evolutionary theory is a framework that explains how all living organisms have changed as a result of evolution and how new species have emerged, based on the factors or mechanisms that influence evolution. Like theories in other scientific fields, evolutionary theory is merely a framework for explaining reality; just as we cannot claim it is absolutely correct, we cannot claim it is absolutely wrong. However, it is no exaggeration to say that it is the most widely discussed theory, offering an alternative to the creationism believed by many. Consequently, scientists who support the theory of evolution have sought to prove it by discovering new information that shapes the theory, while opponents have pointed out its flaws.
The Big Bang is a theory in physics that explains the origin of the universe. It is based on Edwin Hubble’s observation that the universe is expanding; similarly, the theory of evolution provides an explanation for the structure of biological evolution, just as the Big Bang theory explains the origin of the universe. Evolution manifests through the processes of replication, mutation, competition, natural selection, and genetic drift; it was Charles Darwin who first proposed the concept of natural selection. As the theory closest to reality, many people accepted the theory of evolution under Darwin’s influence. However, controversy surrounding the theory of evolution has persisted since the publication of Darwin’s book *On the Origin of Species*. Even today, people’s reactions are mixed, largely because they learn about evolution from various sources and fail to obtain objective information.
Some people mistakenly believe that humans evolved from chimpanzees, but this is a misunderstanding. Evolutionists do not claim that humans evolved from chimpanzees. While chimpanzees and humans are different species, it is believed that they share a common ancestor. This may lead one to wonder how a single animal could transform into entirely new species. A species refers to a group of animals capable of interbreeding to produce fertile offspring, and the offspring produced in this way can also interbreed with one another.
Every living organism is unique, and this is an essential element of evolution. While individuals belonging to the same species may resemble one another in appearance, each possesses slightly different characteristics. These differences arise due to genetics. All living organisms are composed of cells, and cells contain DNA, which holds the information about the organism. This information provides instructions on what the cell should do and how it should do it, determining the characteristics of each organism. Furthermore, every living organism possesses unique DNA. Genes vary slightly from one individual to another, and this is precisely why individuals possess different characteristics.
Nature favors as many subtle differences as possible. The primary cause of an individual’s uniqueness arises during the process of inheritance. Organisms pass on their characteristics to their offspring in the form of DNA, and because recombination and mutation alter the DNA, each offspring appears different from the others. Random recombination and mutation produce individuals with random characteristics, and these individuals interbreed and continue to pass on their traits. This is the reason for the diversity of living organisms today.
This is where natural selection, the core of Charles Darwin’s theory of evolution, comes into play. Among individuals with different traits, nature selects those that are stronger and better suited for survival, while weaker individuals eventually disappear. Individuals with advantageous traits survive and can pass on their enhanced characteristics to their offspring. Ultimately, evolution proceeds in the direction of these enhanced traits.
When explaining the theory of evolution, finches living on isolated islands serve as a good example. Several hundred years ago, a small number of finches migrated to the Galápagos Islands for some reason. This island presented a completely different environment for the finches. With few natural predators, it was a very favorable environment, and they rapidly multiplied, filling the island. Consequently, food on the island became increasingly scarce. Their former companions had now become competitors. It was at this very moment that natural selection intervened. The finches developed differences and distinctiveness through slightly varying beak shapes, which allowed them to avoid competition with their peers. The beaks of some finches evolved to be suited for digging up insects from the ground, while the beaks of others became suited for cracking open seed shells. As a result, the finches were able to avoid competition by occupying distinct ecological niches. They began to mate preferentially with birds occupying the same niche, and over several generations, these traits became more pronounced. Eventually, the differences between the insect-eating and seed-eating finches became so great that they could no longer interbreed. This signifies the emergence of distinct species. Today, there are 14 species of finches on the Galápagos Islands. This demonstrates that each of these finch species originated from a common ancestor.
When we consider the diverse species that originated from a common ancestor in this way, it becomes easy to understand that chimpanzees and humans are different species but share the same ancestor. Evolution does not proceed in a linear chain but has a branched structure like a tree. All living organisms today are located at the tips of the branches, and the common ancestor is at the root of the tree.
Another common misconception about evolutionary theory is the claim that intermediate forms must exist. This stems from the misunderstanding that, in the process of evolution—where a single animal transforms into a completely new species—intermediate forms must exist. For example, consider two species, A and C. Assuming that A is the ancestor of C, people believe that an intermediate species B must be found. However, even if fossils of species B were found, people would argue that an intermediate form between B and C must also be found. This is an argument that repeats endlessly. The fact that the fossil record is incomplete also fuels this misunderstanding. In fact, it is a common lesson in geology that only one in a million organisms becomes a fossil. Furthermore, it is more appropriate to understand the fossils that have been discovered as “key points” in the evolutionary process rather than as “intermediate forms.”
Various views on evolution have existed since ancient times, but Darwin’s theory of evolution is the most widely known. However, evolutionary theory is not limited to Darwin’s theory. Since Darwin, many scientists have put forward various arguments. The theory of punctuated equilibrium argues that evolution does not occur gradually over time but rather rapidly due to sudden natural disasters. The theory of the selfish gene posits that evolution should be understood from the perspective of genes rather than individuals. Modern evolutionary theory considers other evolutionary mechanisms in addition to Darwin’s natural selection and is based on the study of genes and populations.
Evolution is a process, not a result. Darwin’s theory of evolution is the most representative, and it has become more sophisticated with the discovery of genes. However, controversy has persisted as it conflicts with religion regarding the origin of humans. Darwin’s theory of evolution, much like the Big Bang theory, is one theory that explains the process of evolution. Since the accuracy of evolutionary theory cannot be proven, it will continue to be debated in the future.
