DIFFERENTIAL PSYCHOLOGY: HISTORY, PRINCIPLES AND OBJECT OF STUDY - PSYCHOLOGY - 2025

The differential psychology is the area of psychology that deals with studying the differences between the behaviors of individuals and groups. Research in this branch began with the intelligence and heritability studies of Franz Gall in 1800.

The research areas of differential psychology include personality traits, genetics, intelligence studies, motivation, self-perception, individual interests, among others.

The psychology of individual differences examines how people are similar and how they differ in their thoughts, feelings, and behaviors. No two people are exactly alike, but neither are two people who are completely different.

In studying individual differences we try to understand the ways in which people are psychologically similar and, in particular, what psychological characteristics vary between people. Differential psychology is interested in the regularities of differences between people.

For example, when evaluating the efficacy of a new drug, the mean effects in a group in which it has been administered are compared with the effects of another control group in which a placebo (or another type of drug has been administered already known). In this context, the differences between individuals in their reaction to experimental and control chemical manipulations are studied.

The main method differential psychology uses is the scientific method, which follows a number of steps in a logical and rational order through which scientists come to conclusions about the world around us.

In the scientific method, one or more empirically verifiable hypotheses are formulated about what has been observed. A prediction is made about the outcome of the hypothesis, which is empirically verified by experimentation with valid tools (tests, interviews). Following the result of the experiment, it is concluded about the veracity of the hypotheses.

History

The beginnings of the history of the study of individual differences are very old; Plato already wondered why the co-occurrence of certain appropriate characteristics in people was so rare.

Franz Gall and phrenology

However, the most scientific study of differences between individuals dates back to when Franz Gall invented the theory of phrenology in the early 1800s.

Phrenology was a theory of the brain that stated that, by examining the shape and lumps of the human skull, the abilities and traits of each person could be guessed, since each characteristic had its own place in the brain. This study formed one of the first theories about the psychology of individual differences.

Phrenology was so fashionable at the time that by the year 1832 there were already 29 phrenological societies in Great Britain and many magazines and publications in both the United Kingdom and the United States were fully devoted to the study of this field.

It was even seriously proposed to select members of Parliament according to the structure of their skulls. Some phrenologists even molded children's heads to emphasize positive qualities and minimize those considered negative.

Although the phrenologous theory was found to be incorrect, one of its assumptions was correct: the idea that various brain regions have specific functions.

Charles Darwin and Francis Galton

Darwin suggested that nature selects traits that have been successful through the "survival of the fittest" (or the most capable or prepared). His cousin, Sir Francis Galton, concluded that he could apply this principle scientifically.

Why not measure human personality traits and then selectively generate superior people? Galton assumed that human traits, from height and beauty to intelligence and abilities, capabilities, and personality traits, were inherited.

Modern psychology has formalized the study of individual differences in the last hundred years. The psychology of individual differences is still a relatively young science and constitutes a relatively recent development in modern psychology. There are still many debates and problems to solve in this regard, and the information we already have will surely change and evolve.

Since there are multiple and controversial points of view, it is necessary to remain open-minded to adopt alternative perspectives, especially those that are used in the practice of psychology and that have support for research.

Object of study

The psychology of individual differences asks itself two fundamental questions:

• In what ways do we differ from each other?
• Why are people different from each other?

Although answering these two questions is important, the field of differential psychology does not focus on being a descriptive and theoretical area.

Ways are developed to apply the potential of differential psychology to practice, for example to predict outcomes. What characteristics make a person a successful student, for example?

Generating knowledge about how and why people differ from each other and applying it to potentially improve society are the tasks of this field of psychology. Differential psychologists are making great strides in understanding characteristic patterns of affect, behavior, cognition, and motivation.

These patterns could be conceptualized as individual differences in abilities, interests, and temperaments. The future of differential psychology is certainly more promising than it has been for decades.

Principles of differential psychology

In the Western approach to the psychology of individual differences, it is generally assumed that:

• People vary in a wide range of psychological attributes.
• It is possible to measure and study these differences between individuals.
• Individual differences are useful for explaining and predicting behaviors in people.

People can be classified according to their psychological attributes, for example, in relation to their intelligence and personality characteristics, with relative success. However, humans are complex beings and there is still much to explain. There is usually a large number of theories and evidence on differential psychology that sometimes conflict.

Differential psychology and traits

Many of the contemporary personality psychologists believe that there are five basic dimensions to human personality, commonly referred to as "The Big Five" ("The Big Five").

The five traits described by this theory are extraversion, agreeableness / complacency, openness to new experiences, responsibility / conscientiousness, and neuroticism / emotional instability.

David M. Buss, a professor of social psychology at the University of Texas known for his research in evolutionary psychology on individual sexual differences, proposed in his book The Evolution of Personality and Individual Differences the application of the evolutionary principles of differential psychology to the Big Five personality traits. Buss explains why individuals differ in each of the five major traits and the evolutionary value of each of them:

Extraversion

Extraverts are often ambitious, assertive, and competitive, as well as outgoing, physically active, and sexually motivated. High levels of extraversion are associated with a greater number of sexual partners, which increases the chances of survival of the species.

It is also related to a higher social status and greater attention from other people, characteristics that are usually desirable in our species. Extraverted people are also associated with greater physical activity. However, all these characteristics imply a certain level of risk, accidents, illnesses, social conflicts or depletion of resources.

Consistent with this view, people who score high on extraversion have been found to have a higher risk of accidents and arrests and a lower life expectancy than those who score low.

Thus, whether a high extraversion will bring an increase or decrease in reproductive success depends on two things. First, there are characteristics in individuals that determine how much extraversion is optimal.

The more attractive and physically stronger individuals who have good immune function are more optimal for developing an extraverted strategy and dealing with the risks involved.

On the other hand, there may be ecological contexts that generally favor this type of risk taking. When social structures are fluid or the habitat is novel, there can be great rewards for taking risks. When the habitat is stable it is better to be more cautious.

Neuroticism / emotional instability

People who score high on neuroticism tend to have frequent mood swings, are irritable, and anxious. These people face the serious drawbacks of stress-related illnesses and relationship difficulties as a result of their negative affect and high levels of anxiety. This would point to a selection process in the species whose objective was to reduce the level of neuroticism.

However, negative emotions exist for a reason, primarily to detect and deal with threats. The theory suggests that the more prevalent the threats in an environment, the more sensitive the threat detection mechanisms should be, even at the cost of producing numerous false positives, where threats that do not actually exist are detected.

Responsibility / conscientiousness

A high score in this trait is associated with committing to the plans that are carried out, which, in modern environments, has the advantage of leading to high academic and work performance.

Being able to stick to internally generated plans and long-term goals despite distractions may also have been advantageous in some ancestrally relevant contexts, particularly when faced with repeated harvesting and fruit-picking tasks, where results are predictable.

However, some situations cannot be planned or predicted and, in these cases, it is helpful to have the ability to respond spontaneously and without the need for extensive reflection. People who score high on this trait can become very rigid and inflexible, characteristics that reach a damaging extreme in obsessive-compulsive disorder.

It is quite probable, therefore, that the optimal balance between these two extremes depends on the details of the context and the personal role of the individual. This variability would be sufficient to sustain the variation of this trait in individuals.

Kindness / complacency

High friendliness and conformity are associated with high investment in cooperative actions and with great harmony in interpersonal relationships. Humans are a very sociable species, so coordinating with others in joint actions can be highly favored by Darwinian selection.

Therefore, the advantages of high compliance are not difficult to identify. However, there are contexts in which undertaking joint economic actions may be of little benefit. This depends on the resources at stake and the local social structure.

Highly complacent individuals can overinvest in their social relationships, at the expense of their own interests. Many studies conducted in numerous countries have found higher complacency scores in women than in men, a characteristic that has a cultural component as well.

Openness to new experiences

One of the most surprising characteristics of the fifth of the traits is that it is associated in the literature with positive results as often as negative results.

Regarding negative results, a high openness to new experiences is associated with paranormal beliefs, having many contacts with psychiatrists and psychologists, with schizotypal personality disorder and even with psychosis. On the positive side, it is closely related to artistic creativity and, in a weaker way, to intelligence.

Creativity, with a consequent increase in social and sexual attractiveness, represents a key benefit of being open to new experiences, while unusual beliefs and potential psychotic experiences represent a negative cost.

In this case, the ecological context would not be very important when selecting different levels of opening, since these levels are optimal depending on other characteristics of the individual.