Differential psychology, which analyses variations in the behaviour of people, has evolved a lot since Galton founded his Anthropometric Laboratory, a milestone in the study of individual differences. Today this branch of psychology focuses its efforts on determining the relative influences of heredity and environment on behavior.
In this article we will briefly explain the historical development of differential psychology, describe the objectives and methods of this discipline and clarify how it differs from personality psychology , a discipline that is very close in some ways.
History of Differential Psychology
In the mid-nineteenth century the monk Gregor Mendel carried out the first genetic studies that are known. Using peas, Mendel determined the laws of inheritance, made advances for the future concept of “gene” and coined the terms “dominant” and “recessive” in relation to the heritability of biological traits.
A few decades later Francis Galton, a relative of Charles Darwin , became a pioneer of differential psychology and personality through the development of psychometry. Francis Galton’s pupil and protégé, the mathematician Karl Pearson, made fundamental contributions in the field of statistics and questioned Mendelian laws.
The rise of behaviorism led to a decline in the influence of differential psychology, which reappeared in the 1960s and 1970s with the publication of Behavioral Genetics , by John Fuller and Bob Thompson. These authors introduced into differential psychology discoveries of genetics that explained phenomena such as mutations and polygenic transmission.
Despite progress in differential psychology and behavioral genetics, it is still difficult to separate hereditary from environmental influences when studying human behavior and mind.
Objectives of this discipline
The main objective of differential psychology is to quantitatively investigate differences in behavior between individuals . The theorists and researchers in this discipline aim to determine the variables that cause behavioural differences and influence their manifestation.
Differential psychology focuses on three types of variations: inter-individual variations (differences between one person and the rest), inter-group variations, which take into account variables such as biological sex or socioeconomic level, and intra-individual variations, which compare the behaviour of the same person over time or in different contexts.
Despite the fact that differential psychology is often confused with personality psychology, the branch we are concerned with researches very varied topics: intelligence, self-concept, motivation, health , values, interests… However, it is true that the contributions of differential psychology to personality and intelligence are better known.
Since its inception, the psychology of individual differences has been applied in educational and professional settings, although its usefulness depends on the phenomena being investigated. It is also important to mention the usual relationship of differential psychology with eugenics, which aims to “improve” the genetics of populations.
Differential psychology uses mainly statistical methods; thus, we work with large samples of subjects and analyze the data from a multivariate approach . In this way, experimental control elements are introduced that allow relationships between variables to be established. The use of observational and experimental methods is also common.
There are three types of research designs that are characteristic of differential psychology: those that analyze similarities between relatives, designs with animals, and those that study individuals raised in special environments. Of this last type of design we can highlight studies with adopted children, as well as the famous case of the wild child of Aveyron.
Among the family research , studies with monozygotic twins stand out, since they are identical at the genetic level and therefore their differences depend on the environment. However, despite the obvious advantages of this type of design, it is difficult to distinguish the relative influences of the specific and shared environment.
Animal genetic studies can be useful because of the high reproductive rate of some species and the ease of experimenting on non-humans, but they pose ethical problems and the results obtained are often impossible to generalise to people.
How does it differ from personality psychology?
As opposed to differential psychology, which has a mainly quantitative nature, personality psychology focuses its efforts on the causes, characteristics and behavioural consequences of interindividual variability.
On the other hand, the psychology of individual differences does not only analyse personality , but is also interested in other aspects, such as intelligence, socioeconomic variables and certain behaviour patterns, for example criminal behaviour.
In terms of methodology, differential psychology is based more on studies that delimit the relative influence of heredity and environment on certain variables. In contrast, personality psychology uses mainly correlational and clinical methods. Both share the emphasis on experimental methodology.
In any case, the scope of study of these two disciplines frequently overlaps . In the field of temperament and character, personality psychology investigates multiple facets of variations in behavior, while differential psychology quantifies them and also addresses other aspects of human nature.