In ancient and medieval times, the world was viewed in an organic and purposive way, but with the development of modern science, we have come to understand objects by breaking them down into smaller units. The role of nature and nurture in shaping human temperament has been debated, and more recently, the interplay between genes and environment has been recognized as important.
In ancient times, people viewed the world purposively and organically: every object or phenomenon had a purpose or intention, and was an indivisible whole in itself. The ancient Greek philosopher Aristotle believed that all beings have a purpose, and this played an important role in explaining not only natural phenomena but also human behavior. This view persisted through the Middle Ages, and was reinforced by religious worldviews. However, one of the many effects of the development of modern science since the Middle Ages has been the digitization of the world, or the view of objects as being made up of the small units that make up the world. Kepler, for example, explained how we perceive objects by decomposing them into a myriad of point sources of light. Chemistry’s introduction of atomism to explain various chemical phenomena is also a reflection of this view.
This mechanical causalist mindset views nature as a complex, massive machine that operates according to certain laws. It explains many phenomena by decomposing nature into the basic units that compose it and identifying the relationships between these units. Taking this further, there are attempts to explain the phenomena of life in terms of chemistry, just as chemical phenomena are explained by reducing them to the movement of atoms. And today, to a large extent, they are successful. One example is the explanation of emotions as the release of chemical hormones.
Any scientific theory that explains anything requires control of variables and repeated experiments and observations. An example is the relationship between force and motion on an object. To do this, we need to minimize the forces acting on the object, such as friction, to the point where they have no effect, or measure them accurately. Then you need to apply forces to the object, make quantitative observations of its motion, and see how well they match existing theories. These experiments are done by varying the mass of the object and the magnitude of the force.
But can the same scientific method be used to determine the relationship between an individual’s temperament, nature, and upbringing, such as height, weight, IQ, and religious fundamentalism? First of all, there are some things that are difficult to quantify, such as religious fundamentalism, extroversion, and introversion, and the identity of so-called nature is unclear, and nurture cannot be the same every time. Therefore, it is not possible to repeatedly observe what kind of temperament a person will have if their nature is different but their upbringing, or environment, is the same, or if their environment is the same but their nature is different, and therefore it is not possible to experiment with scientific methods. Therefore, the debate about whether nature or nurture plays a greater role in shaping human temperament is not a scientific debate.
The term nature predates the discovery of DNA, so it’s not exactly homologous to DNA. However, DNA is the closest thing to what the term nature refers to. Even before we knew about DNA, Mendel knew that there were independent units that could be passed down from one generation to the next, called genes. People may have misunderstood the genetic laws from soybeans to mean that in humans, there is a one-to-one correspondence between what we think of as human temperament and the genes responsible for it, such as genes for height, genes for weight, genes for IQ, and genes for personality. And since we inherit these genes, we might have thought that our temperament is innate rather than influenced by our environment.
On the contrary, experiments have shown that humans, like Pavlov’s dog, can be made to react differently to their environment through certain stimuli and rewards, and that temperament is shaped by nurture. In this case, we can’t claim that our temperament is caused by the genes that code for weight, or the genes that code for personality. Such a claim would imply that our temperament is determined the moment we inherit our genes, which contradicts what experiments have shown.
Another way to think about it is that inherited temperament can change depending on the environment. So, it’s argued that a certain part of temperament is due to genes and the rest is due to the environment. The experiments in behavioral genetics that compare identical and fraternal twins also don”t provide a direct solution or evidence to the nature vs. nurture debate. It only shows statistically which side is more likely to have a difference in temperament, but it doesn’t tell us what causes an individual’s temperament to develop. In other words, it doesn’t directly say whether nature or nurture plays a greater role.
Does this debate answer the question of nature versus nurture? Perhaps, but in the end, what we really want to know from the nature vs. nurture debate is what makes us who we are and how we are made. The initial question of nature versus nurture may have reflected the idea that the mechanisms that create an organism’s temperament are simple. Also, although Keller argues that it is wrong to dichotomize nature and nurture, what we end up with in our search for an answer to the question is a set of DNA sequences called genes.
The process of “getting” vision, for example, is an example of the interplay between genes and the environment. First, visual information entering the eye travels through numerous pathways to the visual cortex. Once in the cortex, these pathways form a visual dominance column. At first, they’re randomly distributed, then they gradually segregate into column cells that respond only to visual information from the right eye and column cells that respond only to visual information from the left eye. Each of these cone cells must be formed to process visual information correctly to produce vision. This process takes place within the first few months of life, which is called the critical period. If you lose your eyesight during this period, or if your eyes are sutured shut so that you can’t see, the visual dominance columns won’t be able to separate. If only one of the two eyes is blinded, the fovea of the blinded eye will disappear and the cells of the other eye will survive.
Mice lacking a gene called GAD65, which makes a neurotransmitter called GABA, were unable to separate the pathways in the presence of visual stimuli. However, when they were injected with a drug called diazepam, which mimics GABA, the pathways separated. And mice whose genes had been manipulated to produce more brain-derived neurotrophic factor (BDNF) than normal mice responded normally to visual stimuli, even when kept in the dark. In other words, visual experience turns on the gene that produces BDNF.
We don’t yet know exactly how genes play a role in shaping vision, but it’s clear that they interact with the environment. This interaction between genes and the environment allows us to understand complex and sophisticated life phenomena. It also provides important clues to the formation of human temperament, and shows that the nature-nurture debate cannot rely on either factor alone.
Just as Kepler pushed us out of the center of the universe, the course of this debate has reduced us from being thought to be uniquely different from other animals to being no different from amoebas. We are learning that the things that made humans special, such as the existence of nature and reason, are actually the work of genes and tiny parts that turn them on and off at the right time and in response to the environment. To use an analogy, the nurture-nature debate has been like dropping a coin in a dark alley and searching under a distant streetlight for it. Only now have we turned on the light of DNA near where the coin fell, and we are gradually finding it.
In the end, it is the complex interplay of nature and nurture that shapes our temperament. Beyond a simple binary debate, we need a deeper understanding of how the interplay of genes and environment creates our diverse and complex temperaments. This makes future research and exploration all the more important, and we should consider the implications of this understanding for our societies, cultures, and individual human beings.
