In this blog post, we will systematically look at the development of evolutionary theory from Lamarck’s theory of the survival of the fittest to Darwin’s theory of natural selection to modern evolutionary theory.
Why do people live? Where did people come from? Everyone has thought about these questions at least once. This question seems very simple, but at the same time, it is also a problem that many ancient philosophers and theologians struggled with. In the Middle Ages, theology prevailed, and people tried to find an answer to this question through the belief that the Creator created everything, including people, and that all species are created once and forever. In other words, a transcendent being called the Creator was established to solve complex problems. However, as the Renaissance progressed into the 17th century, there was a gradual increase in attempts to explain and understand all natural phenomena with common laws. People began to question the conventional wisdom that living organisms do not change over time by closely observing the living organisms around them. The theory of evolution was born from such thoughts. Now, I will explain how the theory of evolution has developed, how modern evolutionary theory explains how living organisms change, and how evolutionary theory has been used in other fields.
The first to express the idea that living things change in the form of a systematic theory was Lamarck’s theory of the survival of the fittest. In his “Zoology,” written in 1794-1796, Erasmus Darwin argued that “all warm-blooded animals have the power to transform some of their parts, and these improved traits are passed on to their offspring.” Lamarck was influenced by this idea and, in his 1809 book “Philosophical Zoology,” he believed that the traits acquired by living organisms as they adapt to their environment are passed on to the next generation. For example, there was a giraffe that was short in height, but it could reach the leaves it could eat, but it kept stretching its neck to eat the leaves that were higher up. As a result, its neck gradually got longer, and this trait was passed on to its offspring. This process was repeated, and the neck got longer like the giraffe it is today. However, this hypothesis lost its strength when it was discovered that acquired traits are not inherited by genes in germ cells.
The next theory that emerged was Darwin’s theory of natural selection. The theory of natural selection, which was published in 1859 in “On the Origin of Species,” sees evolution as occurring through the process of “individual variation → survival of the fittest → natural selection.” Taking the giraffe as an example, the theory of “long-necked” assumes that the giraffe, which was originally short, gradually grew taller, but the theory of natural selection assumes that giraffes, both tall and short, coexisted from the beginning. At this time, the taller giraffe was able to eat higher leaves, which was advantageous for its survival, and as a result, the taller giraffe was selected, and this trait was passed on to its offspring, leading to the evolution of the giraffe’s height. Darwin’s concepts of individual variation, survival of the fittest, and natural selection provided the most important ideological foundation for modern evolutionary theories and have been widely applied to various fields, including social sciences.
However, the unsolved problem of the theory of Darwin was how traits are passed on to offspring through a process. At the time, the theory of mixed inheritance, which said that the characteristics of the parents would be mixed in half with the offspring, was dominant. However, if this theory is true, then certain traits are passed on to the offspring, but they are diluted during the mating process, which is not in line with Darwin’s theory of natural selection, which states that the characteristics of living things change little by little over time. Darwin proposed the pangenesis hypothesis to solve this problem. According to this hypothesis, a self-replicating particle called a gemmule exists in all cells of an individual, and during reproduction, this gemmule is secreted and passed on to the offspring. However, this too has lost its persuasiveness in that acquired traits are not inherited.
Mendel’s theory of genetics in 1865 completely refuted the theory of mixed heredity. Mendel proposed the theory that an individual has two hereditary factors that determine a specific trait, and that these factors are inherited from the parents one by one through the pea experiment. If the alleles are different, only the dominant gene is expressed, and these alleles are separated during the formation of germ cells and enter into different germ cells, then they pair up again during fertilization. After that, Weissmann clearly distinguished between germ cells and somatic cells and proposed the germ layer continuity theory, which states that heredity is only achieved through germ cells. Eventually, in 1953, Watson and Crick revealed the structure of the genetic material DNA, which clearly explained the process by which traits are passed on to offspring.
De Vries proposed the theory of mutation through the experiment with the dandelion and explained how individual variation is manifested in Darwin’s theory. In addition, Wagner and Romanes argued that evolution occurs through isolation. In the 20th century, modern evolutionary theory was completed with the introduction of population genetics, which identifies evolution through changes in the frequency of specific alleles within a population rather than changes in individual traits, by Hardy, Weinberg, S. Wright, Fisher, and Holdene.
Modern evolutionary theory explains that after individuals in a population are isolated in different environments, various mutations appear due to mutations and hybridization that occur in reproductive cells, and individuals with these mutations undergo natural selection and are reproductively isolated, resulting in the differentiation of different species. In particular, the concept of “gene pool,” which refers to the study of evolution as a population rather than as an individual, emerged through the collective genetics developed by Hardy, Weinberg, S. Wright, Fisher, and Holden. The gene pool refers to the total number of alleles possessed by individuals belonging to a population at a certain time, and changes in the frequency of alleles within this gene pool are interpreted as evolution. Four factors that change the gene pool were proposed: mutation, natural selection, genetic drift, and gene flow. Mutation is a concept borrowed from de Vries’ theory, and it refers to the appearance of new traits as a result of changes in genetic material. Natural selection follows Darwin’s theory of natural selection, and genetic drift refers to a sudden change in the frequency of a certain allele due to an accidental event such as a forest fire. Finally, gene flow refers to a phenomenon in which the frequency of a gene changes due to the introduction of a new allele due to the migration of individuals from neighboring populations.
New theories about evolution are constantly being proposed and existing theories are being re-evaluated. For example, Lamarck’s theory of acquired characteristics is gaining attention again as the claim that acquired characteristics can be inherited through the process of “DNA methylation” is being raised. Research results show that exercise changes the unique DNA methylation patterns in tissue cells, and these changes can be passed on to offspring. Of course, there is still room for debate, but it is clear that the theory of evolution is an ongoing theory with new views emerging all the time.
In addition, the theory of evolution has changed people’s values and had a major impact on many other academic disciplines. Social Darwinism emerged in the 19th century with Herbert Spencer. It argued that survival of the fittest and natural selection also apply to human life, justifying superiority and survival of the fittest. As a result, an inhuman society was formed in which racism was more justified than equality and welfare. Furthermore, some used this to justify colonialism. The theory of evolution has had a significant impact not only on changing perceptions of the nature of human society, but also on ethical values and policies.
