AQA Syllabus focus:
'The biological approach: the genetic basis of behaviour, including genotype, phenotype and evolution.'
The biological approach explains behavior partly through inherited factors. This topic focuses on how genes shape characteristics, how genotype differs from phenotype, and how evolution affects populations over time.
Genes and inheritance
The biological approach argues that some aspects of behavior have a genetic basis, meaning they are influenced by inherited biological information. A gene is the basic unit of heredity and is made of DNA.
Gene: A segment of DNA that codes for a protein and contributes to inherited characteristics.
Genes are located on chromosomes, and humans usually inherit 23 chromosomes from each parent.
This labeled diagram shows the main parts of a chromosome (sister chromatids, centromere, and telomeres) and emphasizes that DNA is tightly coiled and packaged to form chromosomes. It helps connect the idea that genes are segments of DNA and that DNA is physically organized within chromosomes in the cell nucleus. Source
Different versions of the same gene are called alleles. One allele is inherited from the mother and one from the father, so offspring receive a unique genetic combination.
In psychology, genes do not usually produce a single behavior in a simple one-gene-one-trait way. Most behaviors are polygenic, meaning they are influenced by several genes acting together. This is why inherited tendencies are usually described as probabilities or predispositions rather than fixed outcomes.
Genotype and phenotype
A person’s complete genetic makeup is called their genotype.
DEFINITION
Genotype: The genetic constitution of an individual; the set of genes and alleles they inherit.
The genes a person carries do not appear directly in behavior.
Instead, they contribute to a person’s phenotype, which develops through interaction with the environment.
Phenotype: The observable characteristics of an individual that result from the interaction of genotype with the environment.
This distinction is central. Two people can have similar genotypes but different phenotypes because they have experienced different diets, stress levels, parenting, education, or social environments. Likewise, a person may carry genes that increase the likelihood of a characteristic without ever showing it strongly.
In psychology, phenotype includes more than physical appearance. It can include behavioral tendencies, abilities, and vulnerabilities. For example, an inherited predisposition may affect how likely a person is to show a particular trait, but environmental conditions help determine whether and how strongly it appears.
Why the distinction matters
The difference between genotype and phenotype helps explain why biological explanations are not always fully deterministic. A person may inherit a tendency, but that tendency still has to be expressed in real life. This means behavior cannot always be predicted from genes alone.
It also explains why members of the same family can be similar without being identical. They may share some of the same genes, but each individual has a different genotype and experiences a different environment. The phenotype is therefore the outcome of both inheritance and environmental influence.
The genetic basis of behavior
When psychologists say a behavior has a genetic basis, they mean inherited factors contribute to individual differences. This does not mean the behavior is caused entirely by genes. The biological approach usually treats behavior as the product of inheritance working alongside experience.
Because relatives share genes, behaviors that run in families may suggest genetic influence. However, family resemblance alone is not enough to prove inheritance, since relatives often share environments as well. The key idea for this part of the specification is that genes can create biological predispositions that shape behavior.
This view rejects the idea that people are born as blank slates. Instead, it assumes that inherited characteristics influence development from the start. At the same time, the genotype is not a finished set of behaviors; it is a genetic potential that can be expressed differently across environments.
Evolution and natural selection
Over very long periods, inherited variations can change the characteristics of whole populations. This is the basis of evolution.
Evolution: The gradual change in inherited characteristics in a population over generations through processes such as natural selection.
The main mechanism is natural selection. Individuals in a species vary. If a variation increases the chance of survival or reproduction, the individuals who possess it are more likely to pass on the relevant alleles to offspring. Across generations, those inherited characteristics become more common in the population.
This figure compares three classic patterns of natural selection—directional, stabilizing, and disruptive—by showing how the distribution of a trait shifts from one generation to the next. It makes the population-level logic of selection visible: differential survival and reproduction changes how common particular trait values (and the alleles influencing them) become over time. Source
In psychology, this means some behaviors may have been selected because they were adaptive. An adaptive behavior is one that improved survival or reproductive success in ancestral environments. Behaviors linked to avoiding danger, protecting offspring, or cooperating with others may have been favored if they increased the chances of passing on genes.
Evolution works at the level of populations, not single people. An individual does not evolve during their lifetime. Instead, the frequency of inherited characteristics changes across generations when certain traits are passed on more successfully than others.
Linking the ideas together
AQA questions often require these ideas to be connected clearly. Genotype refers to inherited genetic information in an individual. Phenotype refers to the characteristics that are actually expressed. Evolution explains why some inherited tendencies became common in a population over time.
A behavior may therefore be influenced by genes in the present because those genes were successfully passed down in the past. This makes the biological approach both an explanation of individual differences and an explanation of how inherited characteristics develop across generations.
Practice Questions
Briefly distinguish between genotype and phenotype. (3 marks)
1 mark for identifying genotype as a person’s genetic makeup or inherited genes/alleles.
1 mark for identifying phenotype as observable characteristics or expressed traits.
1 mark for making clear that phenotype results from genotype interacting with the environment.
Explain how evolution through natural selection may influence behavior. (6 marks)
1 mark for stating that individuals show inherited variation.
1 mark for explaining that some inherited variations affect behavior.
1 mark for stating that some behaviors are adaptive because they increase survival or reproductive success.
1 mark for explaining that individuals with advantageous characteristics are more likely to reproduce.
1 mark for explaining that relevant alleles are passed to offspring.
1 mark for explaining that, over generations, these characteristics become more common in the population.
FAQ
A gene is a section of DNA linked to a characteristic.
An allele is a specific version of that gene. For example, one gene may influence a characteristic, but different alleles produce variation within that characteristic.
So, all alleles are forms of a gene, but a gene is the broader unit.
Siblings inherit half their DNA from each parent, but not the same half.
This happens because:
egg and sperm cells contain different combinations of chromosomes
fertilization is random
each child receives a unique mix of parental alleles
This is why full siblings are genetically related but usually not identical, except in the case of identical twins.
A mutation is a random change in DNA.
Mutations matter because they introduce new genetic variation into a population. Most mutations are neutral or harmful, but occasionally one gives an advantage. If that advantage improves survival or reproduction, natural selection may increase its frequency over generations.
Without mutation, there would be much less new variation for natural selection to act on.
In evolution, reproductive success means passing genes to the next generation effectively.
It is not just about staying alive. A trait can spread if it helps an individual:
attract mates
produce offspring
protect offspring long enough for them to survive and reproduce
This is why some behaviors may be explained in terms of gene transmission rather than immediate comfort or happiness.
Yes. A trait may still be common because it was useful in earlier environments.
Possible reasons include:
it was adaptive in ancestral conditions
modern environments are different from past environments
the trait may bring both costs and benefits
natural selection does not produce perfection, only relative advantage
This helps explain why some inherited tendencies may seem less useful in modern life than they might have been in the past.
