In this blog post, we will examine how genetics, environment, and their complex interactions shape us as human beings and determine our destiny.
We often have two reactions when we see a student who does well in school. The first is to think that the student is smart and does well in school because they are intelligent. The second is to think that the student does well in school because their parents are wealthy and they have a good environment for studying. In this case, the former sees genetics as the cause of the phenomenon, while the latter sees the environment as the cause. This perspective is not limited to studying. It is also applied to height, personality, various talents, and the onset of disease, and which side is correct has been a long-standing debate in the biological sciences. The reason this debate continues is that both sides oversimplify reality. However, in reality, most phenomena cannot be explained by a single cause, but rather by a combination of various causes, and there are also complex causes that determine what makes a human being. Furthermore, in modern biology, the stubborn belief that genetics or environment alone determines what makes a human being has long since disappeared. In other words, the question of “nature or nurture” is no longer a question of choosing one or the other. From this perspective, it would be reasonable to consider both genetics (nature) and environment together. Therefore, it would be reasonable to view humans as being determined by their nature, which is modified by their environment.
First, let’s look at the evidence to see how strongly humans are influenced by genetics. The first piece of evidence comes from studies on twins. Identical twins have exactly the same genes, so they are an important subject for research on genetics and environment. Bouchard and McGue analyzed more than 100 studies on 50,000 pairs of twins and their relatives to analyze the correlation between intelligence quotient and heredity. In this study, a coefficient called “correlation” was used to quantify the correlation. The closer the coefficient is to 0, the weaker the correlation, and the closer it is to 1, the stronger the correlation. In this experiment, the correlation coefficients between identical twins, fraternal twins, siblings, and parents and children were 0.86, 0.60, 0.47, and 0.50, respectively. Although identical twins and fraternal twins are similar in that they grow up in similar environments, the fact that identical twins, who are genetically identical, have a significantly higher correlation coefficient for intelligence than fraternal twins, who are genetically different, means that genetics has a significant influence on intelligence. This study also shows the correlation between environment and intelligence, which will be discussed in the next paragraph. Another study on twins is that of Thomas Bouchard. After reading an article about twins who were adopted into different homes immediately after birth and met again 40 years later, I decided to investigate twins. The results showed that the two were identical in everything from their habit of biting their nails to their hobby of woodworking and their dislike of basketball. Based on these results, Bouchard continued his research on twins and discovered that habits and personality are strongly influenced by genetics. Another piece of evidence is the existence of geniuses. It is common knowledge that in order to become a world-renowned scholar in fields such as mathematics and physics, one must be born with a talent for that field. The existence of brilliant figures in various fields, such as Einstein, Newton, Da Vinci, and Mozart, confirms that there are innate abilities (genetics) that cannot be surpassed by effort (environment). The influence of genetics can also be seen in the case of the Bernoulli family, who are famous for their mathematical physicists. Despite the recent emphasis on the importance of environment in academia, some scholars still cannot abandon genetic determinism, which is probably related to this fact. In addition, Tony Beron’s research shows that genetics accounts for 52% of personality and habits, while environment accounts for 48%, and research by a team at King’s College London shows that genetics has twice as much influence on academic performance as environment, demonstrating that genetics has a significant influence on humans.
As such, it cannot be denied that genes are an important factor in determining human beings. Biologists have long argued for genetic determinism based on knowledge accumulated over many years, starting with Darwin’s theory of evolution, followed by Watson and Crick’s discovery of the double helix structure of DNA, and continuing to the present day with the Human Genome Project. However, as the genome project has progressed and knowledge about genes has increased, the arguments against genetic determinism have become stronger, and recently, it has lost its usefulness. It has become clear that the idea that approximately 30,000 genes can determine everything about the complex human being is nonsense, and we have also learned more about gene expression. Genes interact with each other and express themselves autonomously, and their expression is influenced by the environment. Therefore, when discussing genes, it is incomplete to ignore the environment, which is a decisive argument against genetic determinism.
So, is the environment the factor that determines humans? Let’s look at the basis for this argument. The first basis is, as mentioned in the section on genes, research on twins. According to the studies by Bouchard and McGue described above, the correlation coefficient between the intelligence of fraternal twins and siblings was 0.60 and 0.47, respectively. The genetic similarity between fraternal twins and siblings is 50%. However, compared to twins who attend the same high school and grow up in similar environments, siblings are born at different times, attend different schools, and grow up in different environments than twins. Furthermore, in today’s rapidly changing world, this influence is likely to be even greater. Therefore, we can conclude that the significant difference in the two correlation coefficients is due to environmental factors. The second argument is based on children raised in the wild. When studying English, you will come across this topic at least once in a reading passage. It is about children who were raised by animals as babies and cannot adapt to society like normal people even after returning to society. There are about 100 known cases of feral boys and girls, with Bello, who was raised by chimpanzees, and Malaya, who was raised by dogs, being representative examples. Belo was raised by chimpanzees for only two years, but he has not been able to adapt well to human society and still behaves like a chimpanzee. Malaya, on the other hand, was 23 years old when the article was written, but her intellectual ability was that of a 6-year-old. She cannot tell time and does not know how to share with others. These wild boys and girls also serve as evidence that language learning occurs largely during early childhood. If genetic determinism is correct, they would be able to return to human society, receive sufficient education, and live like normal people. Another piece of evidence comes from numerous studies on intelligence. There are studies showing that children who have not received formal education have lower intelligence, and that cognitive development is impaired in children who do not eat properly during infancy. However, the most famous study is the Flynn effect. The Flynn effect is a study showing that intelligence increases with each generation worldwide. The increase in intelligence with each generation cannot be explained by genetics. This phenomenon is expected to be due to the fact that society is becoming an environment that requires increasingly intellectual activities.
However, genetic determinism has been proven wrong, and even if there are factors that are influenced by the environment as mentioned above, the influence of genes is too strong to conclude that the environment determines human beings. Therefore, based on the above arguments, it is reasonable to believe that nature, which is modified by the environment, determines human beings, as stated in the introduction. In other words, genes can be seen as potential possibilities that are expressed by the environment. As mentioned earlier, certain traits are determined not by a single gene but by the interaction of multiple genes, and the environment determines the direction in which these genes are expressed. This is consistent with the fact that genes are influenced by the environment when they are expressed. Furthermore, this argument explains the above grounds well. Even if the environment is similar, the difference in expressed traits can be explained by the difference in genes, which means that the potential possibilities themselves are different. Even if the genes are the same, the difference in expressed traits can be explained by the difference in the environment, which means that the potential possibilities expressed are different.
At first glance, this argument seems obvious. However, there is sufficient evidence to support it. The evidence presented above shows that nature alone or nurture alone cannot explain everything, and that both sides are correct when it comes to intelligence. In addition, there are other twin studies that support this argument. This study shows that fraternal twins differ more in extroversion than siblings of the same age. This correlation even appears in identical twins, who are genetically identical. This is because the environment in which siblings of the same age exist causes genes that seek to differentiate themselves to appear. This tendency is found not only in extroversion but also in other personality traits. This is not the only case in which the environment affects gene expression. If you are a science student, you may think of operons when you hear about genes that respond to the environment. Operons are groups of genes that are expressed under the influence of activators that activate genes in a specific environment or repressors that suppress genes. This leads to the question, “Perhaps many genes are not operons, but have a similar structure and are expressed under the influence of the environment?” In other words, it proves that genes that are expressed by the environment as a potential possibility actually exist.
However, current science has limitations in proving this claim. As genetic determinism has revealed its limitations, we may one day discover phenomena that cannot be explained by genetics and environment alone. Furthermore, with current science, it is impossible to accurately analyze these factors using only genetics and environment. This is because genes interact with each other in complex ways, and it is known that the environment, which has a huge number of variables, also affects genes. Therefore, it may be considered premature to argue for either genetics or environment alone. However, it is difficult to return to the question of whether it is genetics or environment. This is because the disadvantages of choosing only one of the two have already been demonstrated in eugenics and reverse discrimination. Stephen Hawking said, “The greatest enemy of knowledge is not ignorance, but the illusion of knowledge.” Modern biology has overcome the illusions of knowledge to transcend human ignorance and present a new paradigm. Examples include Darwin’s theory of evolution, Watson and Crick’s double helix structure of DNA, and the genome project. However, the genome project, which has been in the spotlight until recently, is now showing its limitations. Now is the time for a new Darwin or Watson and Crick. Our role is to judge whether the new paradigm they present is an illusion of knowledge or the key to a new world.
