This blog post examines whether genetic or environmental factors exert a greater influence on the formation of human personality and behavior.
Curiosity about how humans are made has existed since ancient times. Advances in science and technology are gradually unraveling these mysteries. Beginning with Watson and Crick’s discovery of the double helix structure of DNA, the DNA base sequence is being progressively mapped, and research on genes is also actively progressing. Initially, genes were thought to determine only physical traits, but over time, the view emerged that genes also influence the formation of human personality. The debate among scientists regarding human personality formation intensified when Francis Galton first used the term “nature versus nurture.”
Those who believe nature is more important in shaping human personality argue that innate genes cannot change. They believe genes control not only physical traits but also emotions and behavior. These individuals developed a theory known as genetic determinism. Genetic determinism holds that an organism’s behavior is determined by its genetic makeup, asserting that even human social behavior is governed by genes. According to this theory, genetic research can predict how a specific organism will behave, what diseases it will contract, and what physical appearance it will have. As DNA research advanced, the number of people supporting genetic determinism grew. They believed that by unlocking the secrets of genes, they could unravel the mystery of human formation. Supporters of genetic determinism consequently initiated the Human Genome Project. This project aimed to identify and catalog every gene present in the human body. Through it, proponents of genetic determinism sought to prove that numerous genes regulate human formation. This way of thinking stemmed from reductionism. Reductionism is the principle of analyzing complex phenomena by reducing them to simpler phenomena. Modern biology developed based on this reductionist approach. As science advanced, scientists increasingly tended to analyze smaller and smaller units, leading to the discovery of cells and DNA. While this method was excellent as a research approach, it was not appropriate for interpretation. According to the reductionist approach, gene expression is a unidirectional process forming from smaller to larger units. This is called the “Central Dogma,” asserting that DNA is the primary cause determining protein properties in the one-way information transfer from DNA to protein.
However, the findings of the Human Genome Project revealed unexpected results. Genetic determinism suggests humans possess numerous proteins. Considering the genes regulating the activity of these protein-coding genes, human chromosomes should contain at least 120,000 genes. Yet research revealed humans possess only 25,000 genes. This indicates genes do not control everything in humans. Primitive organisms like the nematode Caenorhabditis elegans possess 24,000 genes, while the fruit fly Drosophila has approximately 15,000 genes. This suggests that one gene does not correspond to one trait, meaning genes do not determine everything about humans. Therefore, it is concluded that factors other than genes, or nature alone, play a more significant role in human development.
In opposition to genetic determinism, a new theory called epigenetics emerged. When the Human Genome Project, which began with a reductionist approach, failed to prove genetic determinism, scientists attempted research in a new direction. As a result, it was revealed that environmental influences can alter DNA, i.e., genes. This means that trait formation does not begin unilaterally from DNA but can be regulated by environmental signals. Gene activity is regulated by regulatory proteins, and environmental signals control these regulatory proteins. Research findings showing that environmental signals generate over 2,000 protein variations from the same gene via regulatory proteins also support the involvement of environmental influences in human development. Genes do not directly govern their own activity. Gene expression occurs through the action of effector proteins regulated by environmental signals captured by cell membrane receptors. In other words, the phenotypic expression of a gene is controlled not by the gene itself, but by environmental factors. An experiment involving mice carrying the agouti gene supports this claim. Mice with the agouti gene exhibit yellow fur and obesity. When mice with this gene were fed a diet that blocked gene activity, mother mice carrying this gene gave birth to offspring with brown fur and a lean physique. This demonstrates that the environmental change experienced by the mother mouse also affected her offspring. Gene expression was regulated by the environmental factor of diet. This signifies that genetic determinism is incorrect.
The fact that genetic determinism is flawed can also be seen in historical events. During the Nazi regime, the Holocaust stemmed from eugenics based on genetic determinism. Eugenics is a discipline premised on the existence of superior and inferior genes, studying artificial selection to preserve superior genes. Those who once believed genes determined everything also thought human talents and characteristics were inherited. This gradually led to the classification of people with superior genes and those with inferior genes. In the 19th century, this eugenics spread across many nations, evolving into the classification of racial superiority. It came to distinguish superior races from inferior ones based on genetic differences between races. Ultimately, in Germany, the influence of this eugenics led to the Holocaust, the mass murder of Jews. After these events, the fallacy of eugenics became apparent, and it began to decline. This proved that no hierarchy exists among genes, and that human differences are unrelated to genetic differences. In other words, nature (genes) plays a minor role in human formation.
Now, let’s examine the aspect of nurture. The perspective that nurture is more important than nature is based on environmental determinism. Environmental determinism asserts that the environment plays a more crucial role than genes in human formation. According to this theory, living beings are not entities governed by genes but rather entities that actively change according to their environment. This implies that the flow of information is not unidirectional but occurs through interactions, like a network. In other words, it means that the factors involved in human formation are interconnected and interact with each other. Recent research has shown that proteins within cells interact under the influence of external environments. Environmental determinists emphasize that human formation is shaped by the environment and support epigenetics. Epigenetics asserts that environmental factors regulate gene expression, manifesting as changes in gene expression rather than changes in the genes themselves. Environmental determinism also places great importance on plasticity, the ability of organisms to adapt to their environment.
Genes are crucial factors determining human physical traits and behavior. However, genes are not fixed; they possess the potential to change in response to environmental signals. This suggests that genetic determinism is incorrect. Genetic determinism, based on the assumption that genes remain unchanging, is no longer supported due to the emergence of epigenetics, which demonstrates that gene expression can be altered by environmental influences. The fact that gene expression can be regulated by environmental factors emphasizes that environment (nurture) is more important than nature (genes) in human development. Human development occurs through the interaction of nature and nurture. Genes provide the basic framework for human development, but environmental factors play the role of concretizing and expressing that framework. In human development, genes and environment mutually influence each other to shape the individual.
Identical twins are a prime example of this interaction. Identical twins share the same genes and resemble each other physically. However, raised in different environments, they can develop entirely different personalities. This demonstrates that even with identical genes, human development can vary significantly depending on environmental factors. Another example is Tiger Woods. He is regarded as one of the greatest golfers in history. Tiger Woods’ rise to the pinnacle of golf was due not only to his innate physical talent but also to the environment in which he grew up. His father taught him golf from a young age and invested significant effort in nurturing his talent. It was these environmental factors that enabled Tiger Woods to become the greatest player. In other words, while his innate talent was important, the environmental factors that cultivated it played a more crucial role in his success.
In conclusion, determining whether nature or nurture is more important in human development is a complex question. It is true that genes and environment interact to shape a person. Recent research suggests environmental factors play a more significant role. Genes provide the basic framework for human development, but it is environmental factors that fill and shape that framework. Therefore, the most crucial element in human development is not genes, but rather the surrounding environment in which a person lives.
