Human nature and nurture: Are we determined by our genes or shaped by our environment?

There is a long-standing debate over whether human behavior and personality are determined by genes or shaped by environment and education. Recent research is leading to the conclusion that genes and environment interact to shape human life.

 

For hundreds of years, people in both the East and West have debated whether humans are determined by nature, or genes, or whether they are shaped by nurture, or experiences and education. Nature is represented by genetic determinism, which holds that the behavior of all organisms, including humans, is inevitably determined by a combination of genes. In other words, the behaviors we exhibit are determined by our chromosomes and DNA, and are set in stone at birth. ‘Nurture’, on the other hand, is represented by environmental determinism, which is the opposite of genetic determinism and holds that humans are ‘made’ by their environment after birth. Importantly, neither genetics nor the environment are 100% deterministic, but rather play a leading role, roughly 80:20.
In past class societies, genetic determinists were overwhelmingly dominant because people couldn’t escape the class they were born into, but now that we’re not a class society, the two sides are evenly matched. This “nature vs. nurture” debate intensified as science developed. In the 1800s, with the advent of Charles Darwin’s theory of evolution and his relative Francis Golton’s eugenics, genetic determinism gained even stronger support. The universality of animals, humans, and humanity that Darwin had studied and demonstrated, even if only tenuously, pointed to the role that certain genes played in making animals animal-like and humans human-like. However, in the 1920s, Pavlov’s theory of conditioned reflexes emerged, lending support to the idea that human personality could be changed through mere training. Eugenics was traumatized in the scientific community when it was used as a rationale for Hitler’s genocide of the Jews, and environmental determinism was renewed.
Genetic determinists and environmental determinists have different interpretations of the same experimental results. In 1997, a rat experiment conducted in Canada by Professor Michael Minnie switched the offspring of two mice with different temperaments, and the results showed that the offspring followed the temperament of the nurturing mother rather than that of the original mother. Environmental determinists emphasized the influence of the nurturing mother, arguing that the environment played a more dominant role than genes. Genetic determinists, on the other hand, argued that the mice were not simply changed by the nurturing mother, but that the environment caused certain genes to be expressed.
Toward the end of the 20th century, however, something happened that would end this conflict: advances in science and technology made it possible to analyze DNA, giving the genetic determinists a theoretical basis for their theory, allowing them to interpret phenomena that had previously been analyzed inductively. In particular, the analysis of human DNA gave genetic determinism conclusive support, most notably through the study of twins. Twins are divided into identical and fraternal twins. Identical twins are the result of one egg being fertilized by one sperm and the fertilized egg splitting in two, resulting in cells with identical chromosome pairs and matching DNA sequences. Fraternal twins, on the other hand, are the result of two separate eggs fertilized by different sperm, and their chromosomes and DNA sequences do not match, and they may be of different genders. In short, fraternal twins are siblings born at the same time.
A recent example of twin research is the story of French fashion designer Anaïs Bordier, who in February 2013 was found to be identical. After hearing from a friend that someone who looked like her was an LA actress, Bordier discovered that she and LA actress Thurmansa Futterman were identical twins who shared the same birthday. It is remarkable that despite growing up in different environments, geographically far apart (over 8000 kilometers) in France and the United States, never knowing each other, they had very similar temperaments, such as digestive disorders and eating habits, and both had careers in the arts. There is also the case of the “Jim” twins, studied by Thomas Bouchard in the United States. They were adopted by different families when they were just a few weeks old and reunited at the age of 40. They had the same medical history, the same nail-biting habit, the same occupation, the same personal preferences for gardening, the same family names, and even the same pet dog. It’s a remarkable example of how twins with identical genes can share even the most personal of tastes.
But the first factor that called into question the genetic determinism that twin studies had so strongly supported was the “Flynn Effect. The Flynn Effect is the theory that average IQ rises steadily by at least five points per decade, and it attributes this to advances in education and improvements in nurture and upbringing. However, the Flynn Effect falls short of refuting genetic determinism. Genetic determinism also recognizes the influence of the environment to some extent, and argues that genetic factors play a dominant role. Furthermore, the IQ suggested by the Flynn Effect is based on slightly different standards at different times, and even when measured by the same standardized IQ test, IQ cannot increase indefinitely; there is an upper limit. Therefore, the Flynn Effect is not sufficient evidence to refute genetic determinism.
The second factor is, paradoxically, the Human Genome Project, which began in the 1990s. Given the diversity of human behavioral patterns, it was expected that there would be around 100,000 genes, but in 2001, only around 30,000 were identified. This led Craig Venter, a key figure in the project, to say that “genes alone are insufficient to explain human beings. However, another key figure, Dr. John Thurston, countered that genetic determinism had not suffered a major blow, saying that ‘if you flip a coin 33 times, you get over 10 billion possible outcomes’, meaning that even if, for example, a human behavioral pattern is determined by two genes, 30,000 combinations of genes could produce an infinite number of behavioral patterns.
Finally, the effectiveness of education is a classic rebuttal from environmental determinists. Environmental determinists argue that education allows humans to change the environment in which they live, and that they are active evolving beings. However, this argument reveals a fundamental contradiction in their argument for education. If humans are born with a blank slate, they cannot be educated, which fails to account for human evolution. It also fails to account for human tastes or preferences, or “free will,” which is the ability of humans to choose different outcomes under the same conditions. This is a phenomenon that education alone cannot explain.
Matt Ridley, author of Nature vs. Nurture and renowned science writer, has proposed a new framework called “nature via nurture” to move beyond the nature vs. nurture debate. However, the debate between genetic determinism and environmental determinism is here to stay. While environmental determinism has had tangible evidence both in the past and present, genetic determinism has only recently been studied in the context of human genes, and the deeper the research, the stronger the evidence. Furthermore, the experimental and observational findings of environmental determinism are ultimately based on genes, so it can be said that ‘nature’ reveals its identity through ‘nurture’. Genes are activated through the environment, and the distinction between “nature” and “nurture” may become meaningless.
It’s ironic that this whole discussion is ultimately about denying human beings true free will. The interplay between the absolute control of genes and the external factors of environment leads to the conclusion that human choices are predictable. However, advances in genetic research and psychology will lead to a deeper understanding of human life and behavior, which will contribute to the development of human self-awareness and free will.