Behavioral genetics is a science that studies how our genes influence behavior and the development of our psychological and behavioral traits.

Through comparative studies with twins and adopted children, experts in this scientific field are striving to understand the genetic mechanisms involved in behavior and various diseases.

In this article we explain what behavioral genetics is and what it studies, what its historical background is, its study methods and the main findings arising from this scientific discipline.

Behavioral genetics: what is it and what does it study?

Behavioral genetics, also called behavioral genetics, is a scientific discipline that studies the influence of genetic composition on behavior and the interaction between heredity and the environment as they affect behavior.

Today we know that the vast majority of behaviors studied in psychology are affected by the particular genetics of the individual in question, so it is not so much interesting to know whether genes are important or not, but rather to study the extent to which they affect a specific behavior.

In this sense, behavioural genetics tries to answer questions such as: How do genes and environment interact to influence behaviour? Which specific genes are responsible? What is their mechanism of action? The field of this discipline is advancing rapidly, since we have better and better technological means to observe and study in depth the genes involved in each behavior.

Historical background

The genetics of behaviour, or at least the study of the relationship between behaviour and genetics, has been the subject of interest to many researchers since the end of the 19th century.

It was the English polymath, Francis Galton (Charles Darwin’s cousin), who pioneered twin research and the use of many of the statistical methods of analysis in use today. This scientist carried out the first systematic studies with families, demonstrating how certain behavioural traits could be transmitted and inherited from parents to children.

In the 1960s, several publications based on twin studies and adoption brought to the table the importance of genetic factors in relation to intelligence quotient and some psychiatric pathologies such as schizophrenia. The controversy that arose from the articles published by psychologist Arthur Jensen, who suggested that differences in intelligence were mediated by race, also served as an incentive for behavioural genetics to continue developing as a discipline.

After the more controversial years, the discipline moved from studying race differences to focusing on the influence of genetic factors on individual differences based on constructs such as personality, cognitive abilities or psychopathology. As early as the 1980s, behavioural genetics became established as a full-fledged scientific discipline, and the scientific community supported the importance of heredity in explaining intelligence levels, as measured by an indicator such as IQ.

At present, scientific research related to behavioural genetics is increasingly abundant , thanks to the work of many scientists coordinated in projects such as the Human Genome Project, in which for fifteen years the sequence of chemical base pairs that make up DNA was investigated and nearly 25,000 genes of the human genome were identified.

Robert Plomin, one of the leading geneticists, has suggested that in the next few years the genes responsible for the heritability of behaviour will be identified and we will be able to begin to trace the routes from genes to the brain, and from the brain to behaviour. In addition, the scientist insists that behavioral genetics is the scientific discipline that best interprets the importance of the environment in explaining individual differences.

Study methods

In behavioural genetics, quantitative genetic methods are used to estimate the net effect of genetic and environmental factors on individual differences in any complex trait, including behavioural traits. In addition, molecular genetic methods are used to identify the specific genes that are responsible for a given genetic influence.

Research is conducted on both animals and humans; however, studies using animal models tend to provide more accurate data than research conducted on humans, since both genes and the environment can be manipulated and controlled in the laboratory.

Because of the impossibility of manipulating genes and environment in human research, two quasi-experimental methods are often used to detect genetic influence on individual differences in behavioral traits; the twin method, based on the comparison of monozygotic twins (they are genetically identical to each other and come from the same egg) and dizygotic twins (they developed from two fertilized eggs at the same time).

In studies of twins, if they are monozygotic twins are significantly more similar than dizygotic twins, it means that genes play a determining role in the behavioral trait; that is, to the extent that behavioral variability is caused by environmental factors, dizygotic twins must be as similar for the trait in question as monozygotic twins, since both types of twins are raised by the same parents in the same place and at the same time.
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Another method of study is adoption, in which a quasi-experimental design is made based on the fact that adopted children are separated early from their biological parents, so that it is possible to study the effects separately from nature and nurture. One of the most prominent studies was conducted in 1966 by geneticist Leonard Heston, showing that children adopted away from their schizophrenic birth mothers had the same chance of developing the disease (about 10%) as children raised by their birth mothers with schizophrenia.

Main scientific findings

By using genetically sensitive designs, such as twin studies or adoption studies, research in behavioral genetics has generated several scientific findings over the years . The following are the main findings.

1. All psychological traits show significant genetic influence

Psychological traits have consistently shown a significant genetic influence in the studies conducted, which has led to the description of the first “law” of behavioral genetics .

2. There is no 100% inheritable trait

Although the heritability estimates are significantly higher than 0%, they are also significantly lower than 100% . Heritability percentages are important, usually between 30-50%, but far from 100%.

3. Heritability is caused by the small effect of many genes

Scientific studies show that many genes affect complex traits , such as behaviour. If only a few genes were responsible for the heritability of a trait, the selected lines would separate after a few generations and would not diverge any further in the following generations.

4. The heritability of intelligence increases throughout development

Numerous investigations have shown that the heritability of intelligence (consistently for more than three decades) increases linearly throughout life. A finding made in longitudinal and cross-sectional analyses, as well as in adoption and twin studies.

5. Most effects of the environment are not shared by children growing up in the same family

Although, a priori, it might seem that growing up in the same family makes siblings psychologically similar, the truth is that in most dimensions of behavior and in the development of psychological disorders, it is genetics that is responsible for sibling similarity.

Although environmental effects can have an important influence, they do not trigger siblings growing up in the same family to be similar in their behavioral traits.

Bibliographic references:

  • Gómez, P. (1995). The genetic determination of human behavior. A critical review from the philosophy and genetics of behavior.

  • Plomin, R. 1990. Nature and nurture. An introduction to human behavioral genetics. Pacific Grove, California, Brooks/Cole Publishing Company

  • Plomin, R., DeFries, J. C., McClearn, G. E., Pezzi, L., & Flores, E. A. (1984). Genetics of behaviour. Editorial Alliance.