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Biological Psychology

Biology is defined as the study of life (from the Greek bios meaning ‘life’ and logos meaning ‘study’).

A biological perspective is relevant to the study of psychology in three ways:

1. Comparative method: different species of animal can be studied and compared. This can help in the search to understand human behavior.

2. Physiology: how the nervous system and hormones work, how the brain functions, how changes in structure and/or function can affect behavior. For example, we could ask how prescribed drugs to treat depression affect behavior through their interaction with the nervous system.

3. Investigation of inheritance: what an animal inherits from its parents, mechanisms of inheritance (genetics). For example, we might want to know whether high intelligence is inherited from one generation to the next.

Each of these biological aspects, the comparative, the physiological and the genetic, can help explain human behavior.

Basic Assumptions

History of the Biological Approach

Areas of Application

Stress Gender Development Mental Illness

Investigation of Inheritance

Twin studies provide geneticists with a kind of natural experiment in which the behavioral likeness of identical twins (whose genetic relatedness is 1.0) can be compared with the resemblance of dizygotic twins (whose genetic relatedness is 0.5).

In other words, if heredity (i.e. genetics) affects a given trait or behavior, then identical twins should show a greater similarity for that trait compared to fraternal (non-identical) twins.

There are two types of twins:

Research using twin studies looks for the degree of concordance (or similarity) between identical and fraternal (i.e. non-identical) twins.

Twins are concordant for a trait if both or neither of the twins exhibits the trait. Twins are said to be disconcordant for a trait if one shows it and the other does not.

Identical twins have the same genetic make-up, and fraternal twins have just 50 per cent of genes in common. Thus, if concordance rates (which can range from 0 to 100) are significantly higher for identical twins than for fraternal twins, then this is evidence that genetics play an important role in the expression of that particular behavior.

Bouchard and McGue (1981) conducted a review of 111 worldwide studies which compared the IQ of family members. The correlation figures below represent the average degree of similarity between the two people (the higher the similarity the more similar the IQ scores).

However, there are methodological flaws which reduce the validity of twin studies. For example, Bouchard and McGue included many poorly performed and biased studies in their meta-analysis.

Also, studies comparing the behavior of twin raised apart have been criticized as the twins often share similar environments and are sometimes raised by non-parental family member.

Critical Evaluation

Theories within the biological approach supports nature over nurture. However, it is limiting to describe behavior solely in terms of either nature or nurture, and attempts to do this underestimate the complexity of human behavior. It is more likely that behavior is due to an interaction between nature (biology) and nurture (environment).

A strength of the biological approach is that it provides clear predictions, for example, about the effects of neurotransmitters, or the behaviors of people who are genetically related. This means the explanations can be scientifically tested and ‘proven’.

A limitation is that most biological explanations are reductionist and don’t provide enough information to fully explain human behavior. Individuals may be predisposed to certain behaviors but these behaviors may not be displayed unless they are triggered by factors in the environmental. This is known as the ‘Diathesis Stress model’ of human behavior.


Bouchard, T. J., & McGue, M. (1981). Familial studies of intelligence: A review. Science, 212(4498), 1055-1059.

Darwin, C. (1859). On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life (1st ed.). London: John Murray.

Harlow, J. M. (1848). Passage of an iron rod through the head. Boston Medical and Surgical Journal, 39, 389–393.

Tooby, J. & Cosmides, L. (1992). The psychological foundations of culture. In J. Barkow, L. Cosmides, & J. Tooby (Eds.), The adapted mind: Evolutionary psychology and the generation of culture. New York: Oxford University Press.

Wilson, E. (1975). Sociobiology: The New Synthesis. Harvard University Press

How to cite this article:

McLeod, S. A. (2015). Biological Psychology. Retrieved from

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