What Is Behavioral Genetics

Behavioral genetics is the scientific discipline that deals with the study of genetic influences on behavioral characteristics, understanding these in a broad sense and encompassing observable behavior and cognitive and personality characteristics.

It must be taken into account that the environment contributes to the expression of the genotype: the action of genes is mediated by a large number of biochemical transformations, which, in turn, are influenced by the environment.

Thus, for example, environmental events can alter the hormonal level that can affect the cell nucleus and activate the DNA that causes protein synthesis. Therefore, genotype expression always takes place in interaction with environmental circumstances.

In this article we will learn about some of the most important bases of this complex and useful discipline.

Behavioral Genetics: Genes and the Environment

The genes

Genetics aims to develop methods to establish a relationship or relationships between the expression of a gene and a phenotype. Here it is more precise to speak of probability and genetic contribution. For example, if we have such a form of gene “A” plus that form of gene “B”, plus the gene “C”, then the probability of having the “Z” behavior is “X%”.

The genetic influence of a behavior is difficult to define, except in the rare case of monogenic diseases. In any case, we are dealing with a probability, that is, a degree of uncertainty. If there is a genetic contribution, it is difficult to pinpoint it. We are entering the field of quantitative genetics.

The environment

The larger environment plays a very important role.  This factor is evident for skills that can only be acquired through education. The analysis of environmental causes of behavior falls under the same logic as the analysis of genetic influence.

It can be said that, in each behavior or aptitude there is a genetic contribution (and not of a particular gene) and an environmental contribution. The past of a human being, his education or the society in which he lives, has a strong influence on his behavior. The genetic effect must be combined with the environment. It is just as wrong to say “we are born aggressive” as it is to say “we become aggressive.”

The case of the Joliot-Curie family

The Julio-Curie family is interesting. There has been a succession of Nobel laureates from father to son. The genetic influence is true. But it is not only that: this “Nobel family” has also created a favorable environment. You are more likely to be a Nobel if you work in a laboratory that has already won the Nobel Prize. This means that a great scientist will better convey the way he works.

Therefore, students of great scholars are more likely to be brighter than others. This is an example where the environmental factor is manifest, without denying the genetic contribution.

Behavioral Genetics Methods

The three types of designs to study genetic influence are:

• Those of twins, in which both monozygotic and dizygotic twins are studied.
• Those of the family, in which parents and children or siblings are studied.
• Those of adoption, in which members of the same biological family who have grown up separately are studied. Adopted or genetically unrelated relatives who have been raised together are also studied.

These three types of studies can be combined, allowing a greater amount of information to be obtained. In addition, they make it possible to separate genetic and environmental effects more easily.

Assumptions of behavioral genetics

The methods to estimate the genetic and environmental contribution are based on a series of assumptions or assumptions (Johnson et al., 2008; Munafò, 2009), among which we can highlight the following:

• The shared environment makes people look alike. The unshared environment makes people differentiate themselves.

• The influence of genes on the phenotype occurs in an additive way (rather than multiplicative or interactive). That is, it is assumed that there is a direct linear relationship between the number of common genes and the similarity of personality characteristics. The more common genes, the more similarity and vice versa. Therefore, the genetic contribution of MC twins (who share 100% of their genes) is considered to be twice that of DC twins (who share only 50% of their genes).

• These studies do not consider the possible interactions between genes and the environment.

Evidence on the interaction between genes and environment

There are some clear facts about the interaction between genes and the environment:

• It has been shown that the genetic vulnerability of children may or may not manifest itself, depending on the quality of treatment received by the parents. Thus, it has been found that children adopted with  a schizophrenic biological father were more likely to develop a psychiatric disorder only if they had been adopted by a dysfunctional family.
• In studies of adopted children whose biological parents had a history of crime, only 12% of these children developed criminal behaviors when they were adopted by well-functioning families. The percentage reached up to 40 when they were adopted by families at risk (Collins et al., 2001).

• Individuals with a low income level, but with a high perception of control, and therefore, with the expectation and belief that they can manage their environment, show levels of health comparable to those with high income levels. In genetic studies, on these variables, interactions between genes and environment have been verified, since it has been found that the genetic influence on health decreases as the income level and the perception of control increase.
• It has also been shown that the genetic contribution to life satisfaction decreases as the income level increases (Johnson and Krueger, 2006).
• The genetic contribution in the negative attributional style, which is defined as the relatively stable tendency to explain negative situations through causes that are personal, stable over time and that affect different areas, changes depending on the level of stress. The genetic contribution decreases substantially when we are subjected to low levels of stress, while it increases when their stress level was high.

• For schizophrenia, the genetic contribution is about three-quarters. In autism it is almost 90% of the genetic contribution. In hyperactivity, it also has a genetic contribution of about 80% and about 20% of the environmental share. This is proof that there is no strict and unequivocal determination of the environment or genetics.

Conclusion on behavioral genetics

Let’s not lose sight of the fact that each person is unique. That is, there is a small variation between people that can determine different sensitivities. This is how, for example, some will be sensitive to music and some will not.

Finally, if there is perhaps a genetic basis, the environment also plays an important role. This imposes caution on us when making attributions, even establishing guilt.

Furthermore, scientific analysis of complex phenomena, such as human behavior, cannot provide a complete understanding of these phenomena. Thus, out of necessity, sometimes we find ourselves in the need to accept other more discursive (phenomenological) analyzes in order not to betray reality.