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8.2.10Topic 8 · Grey Matter

Nature vs Nurture in Brain Development — Edexcel A Level Biology A (SNAB) 9BI0 Revision Notes & Topical Questions

5 min read 9 parts Lesson 21 of 22 1 quiz

📚 Edexcel A Level Biology A (SNAB) 9BI0 Hub / Topical Revision
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8.2.10 Nature vs Nurture in Brain Development — Edexcel A Level Biology A (SNAB) 9BI0 notes: Explain how genes and environment interact in brain development and behaviour, using twin and adoption studies.Differences in behaviour and brain function between people could result from…

  • concordance
  • Exam-style question 1
  • Exam-style question 2
  • Exam-style question 3
  • Monozygotic twins
  • Epigenetics

Section 1 of 9The debate

Differences in behaviour and brain function between people could result from nature (the genes inherited) or nurture (the environment, including upbringing, diet, learning and exposure to drugs). Modern biology recognises that both are involved: genes provide a framework and the environment determines how it develops. The question is how much each contributes for a particular characteristic.

Section 2 of 9Evidence for genes

Evidence for genes
Genes control the production of proteins used in building neurones, receptors and neurotransmitters.
  • Mutations can disrupt brain development, as in some inherited disorders.
Some conditions, such as Huntington's disease, are caused by a single dominant allele.
Genes affect the risk of conditions such as schizophrenia, depression and autism,
  • but no single gene is responsible; many genes each add a small effect.

Section 3 of 9Evidence for the environment

1
Experience shapes synapses, as in the visual cortex (critical periods) and in learning and habituation.
2
Enriched environments with toys and social contact increase the number of synapses and brain mass in young rats.
3
Severe neglect in early childhood, for example in institutions, is linked to differences in brain development and behaviour.
4
Prenatal exposure to alcohol, nicotine or poor nutrition can alter development.

Section 4 of 9Twin and adoption studies

Identical (monozygotic) twins share all their genes; non-identical twins share about half their varying genes.

Concordance
Comparing how often both twins show a trait is the concordance.
If identical twins show higher concordance than non-identical twins, a genetic influence is likely.
Because even identical twins do not show 100% concordance for most traits, the environment must play a role.
Adoption studies compare adopted children with their biological and adoptive parents; similarity to biological parents suggests genes, similarity to adoptive parents suggests environment.

Limitations include small samples, shared environments for twins brought up together, and difficulty in measuring behaviour objectively.

Section 5 of 9Gene-environment interaction

Environment can affect which genes are active.

1
Epigenetic changes, such as DNA methylation, alter gene expression without changing the base sequence and can be influenced by factors such as stress.
2
A genetic risk may only produce a condition if the environment triggers it.
3
For example, a person with alleles that raise the risk of depression may be affected only after stressful life events.
4
This is why scientists now ask how genes and environment interact rather than which one wins.

Section 6 of 9Interpreting data and the ethics of research

Data about heritability should be read carefully.

1
A heritability of 0.5 for a trait does not mean that 50% of an individual's trait is genetic; it means that about half of the variation between individuals in that population, in that environment, is associated with genetic differences.
2
Changing the environment can change the value.
3
For this reason, a trait that has a strong genetic component can still be strongly modified by the environment.
4
A condition caused by a single gene,
  • such as phenylketonuria (PKU), is a good example: affected babies cannot break down the amino acid phenylalanine and develop severe brain damage unless they follow a diet low in phenylalanine from birth.
5
The genotype is the cause, but the environment (diet) determines whether damage occurs.

When comparing twin studies, check that the sample size is large enough, that twins were measured in the same way and that the definition of the trait was the same in all participants. Twins raised apart provide a stronger test of genetic influence but are rare, so conclusions are based on small numbers.

Studies of behaviour and genes also raise ethical questions.

Interpreting data and the ethics of research
Results might be misused to label people or to justify discrimination, and parents and teachers might wrongly assume that a trait cannot be changed.
Scientists have a responsibility to report limitations and to avoid claims that go beyond the evidence.
This links back to personalised medicine, where genetic information must be protected and interpreted with care.

Examples from animals support the same conclusion: inbred strains of mice, which have almost identical genes, still differ in behaviour and brain structure if reared in different cages, showing that the environment shapes development even when genes are held constant.

Section 7 of 9Exam-style questions

  1. A study found a concordance for a condition of 60% in identical twins and 15% in non-identical twins. Interpret these data. [3]3 marks

  2. Describe evidence that environment affects brain development. [3]3 marks

  3. Suggest why twin studies may not give a clear answer about the effect of genes alone. [2]2 marks

Section 8 of 9Key terms

TermMeaning
NatureInfluence of inherited genes
NurtureInfluence of the environment and experience
ConcordancePercentage of twin pairs in which both show a trait
Monozygotic twinsIdentical twins from one fertilised egg
EpigeneticsChanges in gene expression not caused by changes in DNA sequence
Enriched environmentSurroundings giving varied stimulation

Section 9 of 9Exam technique

1
Treating nature and nurture as opposites; they interact.
2
Assuming that a 100% genetic effect is shown by any similarity between twins.
3
Forgetting that identical twins share the same genes while non-identical twins share about half the variable genes.
4
Saying a single gene causes complex behaviour.

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