(2026 Exams) The Biological Approach

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Genetics

Every person has a unique genetic code, and this arises through genetic variation. Each gene usually has a number of variations, or alleles, which make up a person's genotype. Each gene helps to shape a person's phenotype, along with their environment.

Unique individuals

While all humans share certain biological mechanisms, we are each unique.
Although our bodies have many of the same parts - brains and hormones and cells with genetic codes - these are expressed in a wide variety of behaviours, thoughts, and reactions.

Genetic variation

Genetic variation, the genetic difference between individuals, is what contributes to a species’ adaptation to its environment.
In humans, genetic variation begins with an egg, about 100 million sperm, and fertilisation.
The egg and the sperm each contain 23 chromosomes containing long strings of genetic material known as deoxyribonucleic acid, or DNA. DNA is made up of many genes.

Genes and alleles

In each chromosome, sequences of DNA make up genes that may control physical traits such as eye or hair colour.
A single gene may have different variations, known as alleles. For example, these alleles may cause the carrier of that gene to have blue eyes or green eyes.
When a sperm and egg fuse, each parent contributes half the genetic information carried by the offspring.
The resulting physical characteristics of the offspring (their phenotype) are determined by the genetic material from their parents (their genotype).

Genes and our environment

Although our phenotype is partially controlled by our genotype, it is actually as a result of a combination of genetic and environmental influences.
Our environment is incredibly important in determining not only when and how our genes express themselves, but also in what combination.

Genetics and Behaviour

Although genes provide an important biological blueprint for our bodies, they can also have an effect on our behaviour. A famous study shows that both our genes and our environment play an important role in the expression of psychological disorders.

Genetics and behaviour

Genes don't only affect our physical characteristics - scientists have found genetic linkages to a number of behavioural characteristics, ranging from basic personality traits to sexual orientation to spirituality.
Genes are also associated with temperament and a number of psychological disorders, such as depression and schizophrenia.
So although genes provide a biological blueprint for our cells, tissues, organs, and body, they also have significant impact on our experiences and our behaviours.

Example study - Heston (1966)

Heston (1966) performed a study looking at adoptees and assessing development of schizophrenia (or other psychotic disorders) depending on whether their biological mothers had schizophrenia and whether they were brought up in a disturbed or healthy family environment.

Study findings

The study found that 36.8% of adoptees whose biological mothers had schizophrenia (high genetic risk) and who were raised in disturbed family environments were likely to develop schizophrenia.
Of those adoptees with high genetic risk but who were brought up in a healthy family environment, only 5.8% were likely to develop schizophrenia.
This gives evidence for the notion that both genetic and environmental factors are necessary for some psychological disorders to develop.

Evolutionary Psychology

Darwin's theory of evolution by natural selection can be applied to the field of psychology. Evolutionary psychologists try to explain psychological traits as survival-enhancing adaptations.

Origins of the theory of evolution

Charles Darwin proposed the theory of evolution by natural selection.
In simple terms, the theory states that organisms that are better suited for their environment will survive and reproduce, while those that are poorly suited for their environment will die off.

Evolutionary psychology

Evolutionary psychology has enjoyed a resurgence in recent decades.
As an approach, evolutionary psychology seeks to explain psychological traits as survival-enhancing adaptations.
To be subject to evolution by natural selection, a behaviour must have a significant genetic cause.
In general, we expect all human cultures to express a behaviour if it is caused genetically, since the genetic differences among human groups are small.

Approaches in evolutionary psychology

The approach taken by most evolutionary psychologists is to predict the outcome of a behaviour in a particular situation based on evolutionary theory and then to make observations, or conduct experiments, to determine whether the results match the theory.
But these types of studies are not strong evidence that a behaviour is adaptive. This is because they lack evidence that the behaviour is in some part genetic and not entirely cultural.

Drawbacks of evolutionary psychology

A major drawback of evolutionary psychology is that the traits that we possess now evolved under environmental and social conditions far back in human history, and we have a poor understanding of what these conditions were.
- Therefore, making predictions about what is adaptive for a behaviour is difficult because they don't need to be adaptive under current conditions.

Predictions from evolution

There are many areas of human behaviour for which evolution can make predictions.
Examples include memory, mate choice, relationships between kin, friendship and co-operation, parenting, social organisation, and status.