In this blog post, we introduce a new perspective on the complexity and diversity of life through two perspectives of evolutionary biology.
There are two main perspectives on evolutionary phenomena in modern evolutionary biology. Both seek to explain the diversity and complexity of life, but they differ in their approaches, central concepts, and theoretical focus. The following article summarizes each position and clearly reveals the scientific implications and differences in perspective. The most central question that evolutionary biology must ultimately explore is how effectively organisms adapt to their environment. Adaptation in organisms does not simply mean survival, but refers to the structural, physiological, and behavioral characteristics that enable them to more successfully survive and reproduce within their species in a changing environment.
This phenomenon of adaptation can best be explained by the mechanism of natural selection, which is why natural selection occupies a unique position in evolutionary biology.
Although natural selection appears to act on biological organisms, its actual target is not the organisms themselves, but rather their biological replicators, genes. A replicator is a unit of information or structure that can replicate itself, and genetically, only genes can fulfill this role. Genes do not function individually, but rather cooperate and combine to form a single living organism. In this process, genes carry and protect themselves, and furthermore, create biological organisms that help them adapt to their environment.
These organisms act as a means for the survival and reproduction of genes, i.e., as “carriers,” and all animals and plants, including humans, are typical examples of such carriers. Genes influence the behavior and physical structure of their carriers, thereby adopting strategies that make their replication more advantageous.
For example, genes that make individuals more sexually attractive to others or that confer energy-efficient metabolic traits are more likely to be replicated at a higher frequency than genes that do not have such traits. In this way, genes increase the adaptability of organisms and gain an advantage in the process of natural selection.
Some genes create favorable conditions for themselves by more actively regulating the external environment of their carriers, i.e., physical, biological, or social conditions. Such genes go beyond simply influencing the internal structure of organisms and use the world outside the organism as a tool for their own replication. Furthermore, in some cases, genes act in ways that are actually harmful to the survival or reproduction of organisms. Despite the fact that such genes can reduce the adaptability of the entire organism, they adhere to their own survival strategy in order to secure opportunities for replication. These so-called “rogue genes” are a representative example of how evolutionary mechanisms do not necessarily coincide with the interests of the organism.
These various genetic strategies clearly show that natural selection does not actually act on individuals, but on replicators, i.e., genes. The evolution of life is a long process that has taken place over millions to billions of years, and in most cases, it has progressed through the gradual accumulation of microevolutionary events through natural selection. Microevolution refers to the process of genetic variation accumulating little by little over generations, resulting in the emergence of the sophisticated and complex life forms we see today.
However, not all evolution has always been gradual. In some cases, organisms of a particular lineage tend to undergo evolutionary changes more easily than those of other lineages. This tendency is determined by the anatomical structure, genetic composition, and reproductive strategy of the organisms in question, and is explained by the concept of “evolutionary potential.” Evolutionary potential indicates how quickly and in how many different directions a particular group of organisms can evolve, and sometimes this itself becomes the subject of natural selection. In this case, selection acts not on a single gene, but on a set of genes or a population, and evolution occurs at a level higher than that of genes.
Meanwhile, another major topic in evolutionary biology is mass extinction. Mass extinction is a phenomenon in which numerous species disappear simultaneously at a certain point in time, bringing about a dramatic turning point in the history of life. For example, it is estimated that more than 90% of all species became extinct during the Permian period at the end of the Paleozoic era, completely changing the composition of the Earth’s ecosystem. In addition, at the end of the Mesozoic era, dinosaurs became extinct due to an asteroid collision, which led to the rise of mammals as the dominant life form on Earth.
The process of species formation cannot be explained simply by the accumulation of gradual changes. New species usually form in small, isolated populations located on the periphery of the central habitat of their parent species. These isolated populations can change rapidly due to interactions with the environment, genetic drift, and bottlenecks, and within a short period of time, they differentiate into new species that are distinct from existing species. Once a species is formed, it often remains stable without major changes for a long period of time. The theory that explains this evolutionary pattern is called punctuated equilibrium. It is based on the observation that genetic changes in large populations do not accumulate easily and tend to remain around the average value. Punctuated equilibrium is consistent with the fossil record and suggests that species evolution is intermittent and discontinuous rather than continuous.
The fossil record also shows that major animal groups appeared in a short period of time through an event known as the Cambrian explosion. At this time, about 530 million years ago, most of the phyla that exist today appeared, and since then, there have been almost no new phyla. This means that although the number of species has steadily increased, the morphological diversity, which corresponds to the basic framework of body structure, has actually decreased. In other words, although the number of species increased, fundamental morphological differences were mostly determined during the early stages and did not change significantly thereafter. This phenomenon is another important example showing that evolution is not simply the accumulation of genes, but is influenced by various factors.
Thus, it is limited to explain the various aspects of evolution solely by natural selection and gradual microevolution. Natural selection remains a key concept in understanding evolution, but other factors such as rapid speciation, long-term stability, and extinction must also be considered as important elements in the broader framework of evolution. The evolution of life is a complex and multi-layered phenomenon that cannot be fully understood by a single mechanism.
Natural selection does not necessarily operate only at the genetic level. In most cases, natural selection occurs at the individual level, and traits that are advantageous for the survival and reproduction of individuals are selected. However, in certain situations, the unit of selection can expand beyond the individual to the group or species level. For example, within a lineage composed of multiple species, certain species may be more resistant to extinction or have a higher ability to diverge into new species. These characteristics act as characteristics of the entire species rather than individual organisms, which is explained by the concept of “species selection.” Species selection provides a new perspective that goes beyond the level of individuals and genes in understanding the history of life and plays an important role in explaining the diversity and complexity of evolution.
In conclusion, modern evolutionary biology does not view evolution as a simple gradual change at the genetic level, but rather as the result of complex interactions at various levels, including individuals, species, and ecosystems. This integrated approach helps to provide a deeper understanding of the origin and evolution of life, as well as the formation and extinction of biodiversity.
