Which determines human traits: heredity or environment?

Discusses the role of heredity and environment in determining human traits. It emphasizes the influence of heredity through twin studies and intelligence research, but also explores the importance of the environment. In the end, it concludes that genetics and environment work together to determine who we are.

 

We often have two reactions when we see a student doing well in school. The first is that the student is good at studying because he or she is smart, and the second is that the student is good at studying because his or her parents are wealthy and have a good environment for studying. In this case, the cause of the phenomenon is genes in the former case and environment in the latter case. This kind of thinking doesn’t just apply to studies. It has been argued in opposition to each other in height, personality, various talents, onset, and so on, and which side is right is one of the oldest debates in biology. The reason this debate is not easily resolved is that both schools of thought oversimplify reality. However, reality is not a single cause, but a combination of many causes, and what makes us human is also a combination of many causes. In addition, modern biology has long since abandoned the idea that genetics or environment are the only factors that determine who we are. In other words, the question of “heredity or environment” is no longer an either/or proposition. From this perspective, it makes sense to think of genetics (nature) and environment together, so that we can see ourselves as determined by our nature, which is modified by our environment.
First, let’s look at the evidence to see how strongly we are influenced by our genes. The first source of evidence is the study of twins. Identical twins are a staple of genetics and environment research because they have exactly the same genes. Bouchard and MCGue analyzed more than 100 studies of 50,000 pairs of twins and their relatives to determine the correlation between IQ and genetics. The correlation is quantified by a coefficient called “correlation,” which is close to zero, indicating a weak correlation, and close to one, indicating a strong correlation. In this experiment, the correlation coefficients for intelligence between identical twins, fraternal twins, siblings, and parents and children were 0.86, 0.60, 0.47, and 0.50, respectively. Although both identical and fraternal twins are identical in that they grow up in similar environments, the significantly higher correlation coefficients for intelligence among identical twins who are genetically identical compared to fraternal twins who are genetically different suggests that heredity has a significant impact on intelligence. This study also shows a correlation between environment and intelligence, which we’ll discuss in the next paragraph. Another study on twins is by Thomas Bouchard. After reading an article about twins who were adopted by different families at birth and reunited 40 years later, he did some research on twins and found that they were identical, from their nail biting habits to their love of woodworking and dislike of basketball. Bouchard continued to study the twins and found that habits and personalities are strongly influenced by genetics. Another source of evidence is the existence of geniuses. It’s common knowledge that to become a world-class scholar in a field like math or physics, you need to be naturally gifted in that field. Einstein, Newton, da Vinci, Mozart, and many others confirm that we have a natural ability (heredity) that cannot be surpassed by hard work (environment). The Bernoulli family, a famous family of mathematical physicists, also shows how powerful the influence of heredity is. This may explain why, despite the recent emphasis on the importance of the environment, some scholars have yet to abandon genetic determinism. Other studies, such as Tony Veron’s research showing that heredity contributes 52% to personality and habits and environment contributes 48%, and a study by a team of researchers at King’s College London in the UK showing that genes have twice as much influence on grades as environment, show that genes have a significant impact on human beings.
There’s no denying that genes are an important part of who we are. Biologists have long argued for genetic determinism based on years of knowledge, starting with Darwin’s theory of evolution, through Watson and Crick’s DNA double helix, and up to the Genome Project. However, as the Genome Project has progressed and our knowledge of genes has increased, the arguments against genetic determinism have become stronger and stronger, and in recent years, they have lost their effectiveness. The idea that a set of about 30,000 genes can determine everything about a complex human being has been challenged, and we’ve learned more about gene expression. Genes interact with each other, express themselves autonomously, and are influenced by the environment during the expression process. Therefore, discussing genes without considering the environment is only half the story, which is a conclusive argument that genetic determinism is wrong.
But does the environment determine who we are? Let’s look at the evidence for this claim. The first source of evidence is the same as we mentioned with genes: twin studies. In the study by Bouchard and MCGue described above, the correlation coefficient of intelligence between fraternal twins and siblings was 0.60 and 0.47, respectively. The genetic similarity between fraternal twins and siblings is 50%. However, unlike twins, who attend high school together and grow up in a similar environment, siblings are born at different times, attend different schools, and grow up in different environments than twins. In today’s fast-paced world, this effect is likely to be even greater, so we can conclude that the significant difference between the two correlation coefficients is due to environment. The second source of evidence is children raised in the wild. This is a topic that you may have come across in reading texts while studying English: children who are raised by animals as babies are unable to adapt to society as adults. There are more than 100 known wild boys and girls, including Bello, who was raised by chimpanzees, and Malaya, who was raised by dogs. Bello was raised by chimpanzees for only two years, but he hasn’t adapted well to human society and looks more like a chimpanzee. Malaya was 23 years old at the time of this article, but had the intellectual capacity of a 6-year-old, couldn’t read a clock, and didn’t know how to share with others. There is also evidence to suggest that these wild boys and girls learn language at an early age. If genetic determinism is correct, they could return to human society and be educated in enough time to live like normal people. Another source of evidence is the many studies on intelligence. There are studies that show that children without formal education have lower intelligence, and studies that show that poor feeding in infancy leads to poor cognitive development. But the most famous study is the Flynn Effect. The Flynn Effect is a study that shows that intelligence increases across generations worldwide. This increase in intelligence over the generations cannot be explained by genes. This phenomenon is thought to be due to the fact that society is becoming increasingly intellectually demanding.
However, genetic determinism has been proven wrong, and even if there are some things that are determined by the environment, as shown above, the influence of genes is too strong to assume that the environment determines us. Therefore, based on the above evidence, it is reasonable to assume that our nature, as modified by the environment, determines us, as stated in the introduction. In other words, we can think of genes as potential possibilities and the environment as their expression. As mentioned earlier, a trait is not determined by a single gene, but by the interaction of genes, and the environment determines the direction in which multiple genes are expressed. This is consistent with the fact that genes are influenced by the environment when they are expressed. This argument also explains the evidence above. Different expressed properties in similar environments can be explained by different genes with different potentials, and different expressed properties in the same environment can be explained by different environments with different potentials.
At first glance, this seems like a claim that anyone could make. However, there is plenty of evidence to support it. All of the evidence above suggests that neither nature nor nurture alone can explain everything, especially when it comes to intelligence. Furthermore, there are other twin studies that support these claims. This study found that fraternal twins show more differences in extroversion than older siblings. This correlation is even seen in genetically identical twins. This is due to the environment of having a sibling of the same age, whose genes are more inclined to differentiate themselves. Moreover, this tendency is not only found in extroversion, but also in other personalities. This is not the only case where the environment affects the expression of genes. If you’re a science or engineering student, you may recognize operons as environmentally responsive genes. An operon is a family of genes that are expressed under the influence of either a promoter, which activates the gene, or a repressor, which inhibits the gene, in a particular environment. This leads us to think, “Maybe many genes are not operons, but are expressed in the same structure, under the control of the environment?” In other words, it proves that there are indeed genes that are expressed by the environment, as a potential possibility.
However, there are limitations to this claim based on current science. Just as genetic determinism has been shown to have its limitations, we may one day discover phenomena that cannot be explained by genetics and environment alone. Furthermore, our current science is not capable of analyzing genetics and environment in a precise way. We know that genes interact with each other in a complex way, and that the environment, with its enormous number of variables, also affects genes. Therefore, it may seem simplistic to argue for only genes or only the environment. However, it is difficult to return to the issue of heredity or environment as an either/or, because the consequences of choosing only one or the other have already been shown in eugenics and reverse discrimination. ‘The greatest enemy of knowledge is not ignorance, but the illusion of knowledge,’ said Stephen Hawking. Modern biology has come up with new paradigms to overcome the illusions of knowledge in order to overcome human ignorance. Darwin’s theory of evolution, Watson and Crick’s double helix structure of DNA, and the Genome Project are examples. However, the Genome Project, which was the center of attention until recently, is now showing its limits. It’s time for a new Darwin or Watson and Crick. Our job is to determine whether their new paradigm is an illusion of knowledge or the key to a new world.