In this blog post, we will examine why identical twins with the same genes grow up differently.
Identical twins are genetically identical unless a mutation occurs. However, can we say that these twins are identical even if they are raised in different environments? We cannot say that without further investigation. Depending on the environment, one twin may be taller, or the two may have completely different personalities. Additionally, only one of the twins may develop a disease like cancer. Why is that? After all, they were born to the same parents and even from the same egg and sperm. Did the parents’ genes not properly pass on to the identical twins? Richard C. Francis would say, “Half right, half wrong.” Twin studies have long been an important tool for understanding the interaction between genetics and the environment. These studies have shown that genes do not determine everything, and that environmental factors can have a significant influence on biological expression. For example, people with certain genes may face a higher risk of disease when exposed to specific environments.
Thus, the interaction between genetics and environment requires an understanding not only of genetic factors but also of how they are expressed.
Biological inheritance, as commonly understood, refers to the phenomenon of traits being passed from parents to offspring. Traits are inherited through the chromosomes in sperm and eggs. In other words, genes are determined at the time of conception and are not influenced by external factors thereafter. However, Richard C. Francis offers a slightly different perspective on biological inheritance. Unlike classical inheritance, he argues that genes continue to change even after fertilization and birth. To be precise, the genes themselves do not change, but their expression does. This is why the statement “half true and half false” was made in the previous example.
Modern genetics no longer views genes as mere biological codes. Gene expression can vary depending on the microenvironment of cells, nutritional status, stress levels, and even an individual’s lifestyle habits. These changes in gene expression accumulate over a lifetime and can even influence future generations. This is particularly evident in the field of epigenetics.
For example, people born during a famine in the Netherlands were more susceptible to obesity and heart disease. However, there was no problem with their genes themselves. It was the epigenetic changes in response to the environment that made them more susceptible to disease. Another example is calf rearing technology that utilizes the metabolic imprinting effect. The metabolic imprinting effect refers to the phenomenon where nutritional or hormonal changes during the early stages of life permanently influence the body’s physiological metabolism. Feeding technology is a technique that involves providing specific nutritional stimuli during a certain period in the early stages of life to promote the development of specific body parts in calves, thereby enabling the production of high-quality meat in a short period of time.
Such epigenetic mechanisms also play a significant role in human diseases. Chronic diseases such as cancer, diabetes, and heart disease are not merely the result of genetic predisposition but are closely related to an individual’s early life experiences, nutritional status, and stress levels. In particular, mental factors such as stress can promote epigenetic changes that regulate gene expression. This suggests that not only the genetic information passed down from parents to children but also their lifestyle can influence the health of their offspring.
Through such examples, Richard C. Francis argues that an epigenetic approach can offer various benefits, such as disease treatment and species improvement. While this is a valid argument, I do not believe that an epigenetic approach is the only solution to the problem. Let us examine the examples from the book. The book addresses mental issues such as stress and lack of affection. Let us consider the example of gorillas. Gorillas separated from their parents at a young age and left to fend for themselves exhibit social deficits and have difficulty with sexual behavior. Gorillas raised by humans show slightly less social deficits but generally exhibit similar patterns. In particular, female gorillas are significantly impaired in their ability to raise offspring. In such gorillas, it is said that NGF in the hippocampus is altered, making them vulnerable to stress. NGF stands for Nerve Growth Factor, which regulates the speed and manner of nerve growth. Richard C. Francis argues that parental neglect has produced epigenetic effects.
Epigenetic influences are not negligible in humans either. Extreme stress or abuse experienced during infancy can lead to various mental health issues such as mental illness, anxiety disorders, and depression in adulthood. This is not merely a psychological issue but can also involve biological changes such as structural changes in the brain and imbalances in neurotransmitters. From this perspective, epigenetics offers new possibilities for mental health research and treatment.
My question was whether such issues could be explained by something other than epigenetics. Parental neglect significantly influences personality and social skills. This can be understood through psychological approaches without necessarily resorting to an epigenetic perspective. Vivan Gadsden and Aisha Ray, PhDs from the University of Pennsylvania, found that children whose fathers actively engaged in communication and parenting demonstrated superior cognitive abilities.
Even without this specific example, there are countless similar cases where good parenting leads to healthier and more capable children. Such psychological approaches demonstrate the importance of emotional bonds between parents and children. However, it is also worth considering that these psychological factors may actually cause physiological changes through gene expression.
In other words, psychology and epigenetics are not opposing fields but rather complementary ones. From an epigenetic perspective, psychological stress and emotional experiences can directly influence gene expression, playing a significant role in long-term health.
This phenomenon can also be explained through trauma theory. Children who are neglected or abused while growing up exhibit physical and emotional symptoms of anxiety. When these children become adults, they often have personality disorders that make it difficult for them to form healthy relationships. Based on this, it can be inferred that the experience of neglect or abuse during childhood remains as trauma, making it difficult to provide appropriate parenting when they marry and have children.
Trauma theory is closely linked to epigenetics. Psychological wounds from childhood can go beyond mental suffering and affect physiological changes, particularly brain development. As a result, adults may experience difficulties regulating their emotions or reacting excessively to stress, among other issues.
These epigenetic changes can also affect their children, providing important clues to understanding the psychological and physiological wounds that are passed down across generations. Let’s look at another example from the book, this time dealing with cancer. The book explains the occurrence of cancer in Tasmanian devils as an epigenetic cause.
Cancer is essentially foreign to our bodies, meaning it is an external substance. Our bodies naturally trigger an immune response to foreign substances. However, in the case of Tasmanian devil cancer, this immune response does not occur. This is because the cancer affects the immune system’s recognition stage, rendering the cells responsible for identifying external cancer cells inactive.
This immune evasion mechanism is a very important topic in cancer research. Studies on how cancer cells evade immune system surveillance provide crucial information for the development of immunotherapy. Cancer is the result of complex interactions between genes and the environment, and epigenetic changes may play a significant role in these interactions. Epigenetic variations often induce gene expression changes necessary for cancer cells to grow and spread. This process can be triggered by environmental factors, stress, or even specific drugs.
But does this necessarily require an epigenetic explanation? Of course, cancer does affect the genes of Tasmanian devils. However, I wondered if this could also be explained by the body’s response to self and non-self, or to chemicals or other stimuli, rather than epigenetics.
Could there be other reasons for immune suppression besides genetic factors? While this does not mean that the immune system is directly destroyed, as in the case of AIDS, which destroys white blood cells, I believe that approaching the issue from a different perspective could be an effective strategy. Cancer research requires multiple approaches. Genetic, environmental, epigenetic, and immunological factors all interact and influence the development and progression of cancer. To understand immune evasion, we must consider not only genetic factors but also epigenetic changes, environmental factors, and the complex interactions of the immune system. The stability of epigenetics is also an issue to consider. One of the main concepts of epigenetics is methylation (the attachment of methyl groups to genes) and demethylation (the opposite of methylation).
It is claimed that methylation can be reversed at any time. Additionally, since epigenetics does not directly affect genes themselves but rather regulates gene expression, it is argued that genetic inheritance between parents and children may not be well-preserved. However, as seen in the example of the Dutch famine mentioned earlier, the famine experienced by the grandmother’s generation had an impact on the grandchild’s generation.
It is reported that the obesity rate and incidence of adult diseases in the grandchild generation were higher than in those who did not experience the famine. Given this, it is questionable whether an epigenetic approach can be considered safe. The fact that epigenetic changes can be transmitted across generations requires caution in the application of this field of study. Epigenetic variations can potentially affect health across generations, leading to both positive changes and negative outcomes. Therefore, treatments or interventions utilizing epigenetics must be carefully reviewed for their potential risks and fully reflect ethical considerations. Epigenetics is still in its infancy. In fact, it is too early to judge its practicality or efficiency. However, rather than thinking about treatments or accessibility at this early stage, it would be better to focus on research into epigenetics itself. I hope that we can discuss practical applications once epigenetics has become more established. The future of epigenetics is limitless. This field of study can provide new insights into human health and disease and play an important role in the development of personalized treatments.
