In this blog post, we will look at the debate surrounding whether human behavior and personality are determined by genes or shaped by the environment.
For hundreds of years, humanity has been debating whether human nature is determined by genes or shaped by the environment of nurture, such as experience and education. “Nature” is represented by genetic determinism, which is the view that the behavior of not only humans but also all organisms is inevitably determined by the combination of their genes. In short, the position is that the behaviors that humans show from birth are determined by chromosomes and DNA, and are already set at birth. On the other hand, “nurturing” is represented by environmental determinism, which is the opposite of genetic determinism, and is the view that humans are “made” by their surroundings after they are born. For example, education is considered to shape a person. What is important is that genetics and environment do not determine everything, but play a leading role in about 80:20.
In the past, class society was such that people could not escape the class they were born into, so genetic determinists were overwhelmingly dominant, but now that we are not in a class society, the conflict between the two sides is intense. This debate over “nature and nurture” has intensified as science has advanced. In the 1800s, the theory of evolution by Charles Darwin and the eugenics of his relative Francis Galton emerged, giving genetic determinism even stronger support. The universality of animals, humans, and humanity that Darwin studied and proved gave a glimpse of the role that certain genes play in making animals animals and humans humans, albeit weakly. However, with the emergence of Pavlov’s theory of conditioned reflexes in the 1920s, the claim that training alone can change human personality gained support. Eugenics became a trauma in the scientific community when it was used as a justification for Hitler’s genocide of the Jews, and environmental determinism was re-examined in the light of this.
Even when the results of the same experiment are presented, genetic determinists and environmental determinists offer different interpretations. In a 1997 experiment conducted by Professor Michael Mine in Canada, two rats with different tendencies were raised together, and the results showed that the offspring followed the tendency of the mother who raised them, rather than the tendency of the mother they were born to. In response to this result, environmental determinists emphasized the influence of the mother and argued that the environment plays a more dominant role than genes. However, genetic determinists explained that the mice in this experiment did not change simply because of the influence of the mother, but that certain genes were expressed depending on the environment.
However, at the end of the 20th century, an event occurred that put an end to this conflict. With the development of science and technology, DNA could be analyzed, and genetic determinists were given a theoretically valid basis. Phenomena that had been analyzed inductively could now be interpreted on a theoretical basis. In particular, genetic determinism has been decisively supported by the analysis of human DNA, and the twin study is a representative example. Twins are divided into identical and fraternal twins. Identical twins are formed when one egg and one sperm are fertilized and the fertilized egg is divided into two, and they are composed of cells with identical pairs of chromosomes and their DNA sequences are identical. On the other hand, fraternal twins are created when two eggs are fertilized by two different sperm, so the chromosomes and DNA sequences do not match and the gender may also be different. Simply put, fraternal twins are brothers born at the same time.
A recent example of twin research is the story of French fashion designer Anais Bordier in February 2013. After hearing from a friend that someone who looked like her was an actress in Los Angeles, Bordier discovered that she and the actress Samantha Potterman were identical twins who had the same birthday. It is surprising that the two people, who grew up in different environments and knew nothing about each other in geographically distant places (more than 8,000 km apart) in France and the United States, had very similar temperaments, such as digestive disorders and eating habits, and had professions in the arts. There is also the case of the “Zim” twins, which was studied by Thomas Budger in the United States. They were also adopted by different families within a few weeks of birth and reunited at the age of 40. It is said that they even shared the same military service record and the habit of biting their nails. The shape of the garden, which reflects the careers and personal tastes of the owners, and even the names of the family members and their pet dogs matched. This is a remarkable case in which twins with identical genes even share the same extremely personal tastes.
However, the first factor to question genetic determinism, which was strongly supported by twin studies, is the Flynn effect. The Flynn effect is a theory that the average IQ steadily increases by at least five points every ten years, and it is argued that this is due to advances in education and improvements in the environment for upbringing and growth. However, the Flynn effect is not enough to refute genetic determinism. Genetic determinism also acknowledges the influence of the environment to some extent, and claims that genetic factors play a leading role. In addition, the IQ presented in the Flynn effect varies slightly depending on the time period, and even if measured with the same IQ test, the IQ cannot increase infinitely, and there is an upper limit. Therefore, the Flynn effect is not sufficient as a basis for refuting genetic determinism.
The second factor is the Human Genome Project, which ironically began in the 1990s. Given the diversity of human behavioral patterns, it was expected that there would be about 100,000 genes, but the results, which were revealed in 2001, were about 30,000. In response, Craig Venter, a key figure in the project, said, “Genes alone are far from enough to explain the human being.” However, another key figure, Dr. John Sulston, countered that genetic determinism was not significantly affected, saying, “If you throw a coin 33 times, you get more than 10 billion possible outcomes.” For example, even if a human’s behavior pattern is determined by two genes, it means that 30,000 gene combinations can create an infinite number of behavior patterns.
Finally, the effect of education is a representative counterexample to environmental determinists. Environmental determinists claim that humans change their environment through education and are actively evolving beings. However, this claim actually reveals the fundamental contradiction of the education they claim. If humans are born with a blank slate, education cannot be done, and this does not explain human evolution. It also does not explain human preferences or tastes, which are the choices of different outcomes under the same conditions, that is, “free will.” This is a phenomenon that cannot be explained by education alone.
Matt Ridley, author of “Nature and Nurture” and a renowned science writer, has proposed a new framework, “nature via nurture,” to transcend the nature versus nurture debate. However, the debate between genetic determinism and environmental determinism will continue. Environmental determinism has provided visible evidence in the past and present, while genetic determinism has only been studied in humans relatively recently, and the more research is conducted, the more solid the evidence becomes. In addition, since the experimental and observational results presented by environmental determinism are ultimately based on genes, it can be said that “nature” reveals its identity through “nurturing.” Genes are activated through the environment, and the distinction between “nature” and “nurturing” can become meaningless.
It is ironic that all of these discussions ultimately deny the existence of true human free will. The interaction between absolute control of genes and external factors of the environment leads to the conclusion that human choices are predictable. However, the development of genetic research and psychology will deepen our understanding of human life and behavior, which will contribute to the development of self-awareness and free will.
