Why does the same event provoke completely different reactions? Why does one person calmly accept criticism, while for another it becomes a strong emotional experience? Why does someone freeze in a dangerous situation, someone else runs away, and another person starts to act?

Very often we try to explain a person through simple oppositions: is it innate or acquired, biology or psychology, genetics or upbringing. In reality, this is a fallacy.

A person is a complex biopsychosocial system. When we talk about emotions, behavior, or psychological reactions, we are always dealing with the interaction of many levels: genetics, the functioning of the nervous and endocrine systems, prior experiences, environmental conditions, basic physiological needs, and social context.

That is why modern biology does not favor simple answers. They may be convenient, but they almost always lose a significant part of what is actually happening.

When we talk about biology, it often seems that it is exclusively about genes. But this is only part of the story. Genetics sets certain possibilities, but how they are realized depends on many factors. I like the comparison: genetics is the text, and epigenetics is the way it is read. The same text can be read differently. Similarly, different regions of the genome can manifest more strongly or weakly depending on life conditions, experiences, or environment.

To this, we add the characteristics of early development, childhood experiences, lifestyle, sleep, physical activity, nutrition, the state of the microbiome, and also factors that we do not control, such as living in conditions of war or prolonged stress.

Therefore, any of our reactions is not the result of the work of some single mechanism, but the sum of the interaction of many systems.

The word "sensitivity" can be used differently by various specialists. As a cellular biologist, I would primarily talk about the sensitivity of receptors.

When we hear about dopamine or serotonin, it seems that the main thing is the amount of these substances. In reality, a neurotransmitter is just a molecule. For it to work, it needs to bind to a receptor—a kind of "lock" on the cell. Only after that does a cascade of processes begin, which forms the cellular response.

There can be several different receptors for one neurotransmitter, and each of them can have different sensitivity. Moreover, this sensitivity depends on both genetic characteristics and environmental influences.

That is why popular explanations like "more serotonin is better" or "less dopamine is worse" overly simplify reality.

In fact, this concerns two different situations. The first is when one event provokes different reactions in different people. The second is when the same person reacts differently to the same event at different times.

Different people have different genetic characteristics, different experiences, and different states of the nervous system. Therefore, reactions can vary significantly.

But even one person does not always react the same way. It matters whether they have had enough sleep, how tired they are, whether their basic needs are met, and whether they are taking certain medications. For women, an important variable can also be the phase of the menstrual cycle.

In other words, the brain never works in a vacuum. It always reacts in a certain psychophysiological state.

Freeze, fight, and flight are three basic evolutionary strategies for responding to threats. But it is important to remember: these are not types of people.

The same person can initially freeze to assess danger, then run away, or conversely, start actively defending themselves depending on the situation. Which reaction occurs first depends on a combination of many factors: prior experience, characteristics of the nervous system, current state of the body, and specific context.

Therefore, these reactions should not be seen as rigid categories. In reality, they are very dynamic and can transition into one another. And there is no "correct" one here. From a scientific point of view, the concept of a "normal reaction" is not very accurate.

In biology, the norm is not one correct answer, but a certain range of adaptability. For example, sometimes the best solution is to freeze, and sometimes it is to act as quickly as possible. The effectiveness of a reaction is determined not by the reaction itself, but by the situation in which it arises.

That is why evaluating a person's behavior should not be done by template, but in a specific context.

Our brain does not just react to events. It constantly compares new information with previous experiences and uses it for prediction. In this process, neuroplasticity plays a key role, which includes the brain's ability to reorganize its connections under the influence of experience.

That is why the same situation can mean completely different things for different people. For someone, criticism will become a stimulus for development, for someone else, a signal of danger, and for someone, it will simply not matter much. This is not about strength or weakness of character. It is the result of how the information processing system has been formed throughout life.

Modern neurobiology already explains many general patterns of brain function well. But it cannot yet predict the reaction of a specific person in a specific situation. The reason is simple: genetics, experience, physiological state, event context, and dozens of other factors interact simultaneously.

Therefore, today science can talk about trends and probabilities, but not about precise predictions.

Perhaps the main conclusion lies precisely in this: one should not look for simple explanations for complex human behavior. Our reactions are never determined by just one factor. They are born at the intersection of genetics, brain function, prior experience, physiological state, and environment. It is this complex interaction that makes each person unique.