Theory of evolution (biology only) — AQA GCSE Biology
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Theory of evolution (biology only) explained
This statement corrects an early idea about how characteristics pass from parents to offspring.
Read the full explanation
Lamarck proposed that features acquired during an organism's life, such as a giraffe stretching its neck to reach high leaves, could be inherited by its young. We now understand that most body changes gained during life are not written into the gametes, so they are not passed on. Only changes to the DNA of gametes, such as new alleles formed by mutation, can be inherited. A stretched neck therefore does not make a longer-necked calf. The rare exceptions involve epigenetic marks or environmental effects on gametes, but these are not the main route of inheritance.
Your focus
- Describe Lamarck's idea that characteristics acquired during life can be inherited.
- Explain why most acquired characteristics cannot be inherited because they do not change gamete DNA.
- Use a named example to show that this type of inheritance is rejected in the vast majority of cases.
Theory of evolution (biology only) exam tips
Quick Revision Summary (Key Takeaway)
Charles Darwin proposed the theory of evolution by natural selection, stating that all species of living things evolved from simple life forms that first developed more than three billion years ago. In AQA GCSE Biology, students must understand Darwin's theory alongside Jean-Baptiste Lamarck's competing hypothesis and the historical reasons why Darwin's ideas were only gradually accepted.
Topic Overview
The 'Theory of evolution (biology only)' topic examines the historical development of evolutionary biology, contrasting Charles Darwin's theory of natural selection with Jean-Baptiste Lamarck's hypothesis of acquired characteristics. It explores the cultural and scientific barriers that delayed the acceptance of Darwin's ideas following the 1859 publication of 'On the Origin of Species'.
Understanding this topic helps students appreciate how scientific theories develop, face peer scrutiny, and become established paradigms when corroborated by new evidence. It connects directly with wider GCSE themes including genetics, speciation, fossil evidence, and modern classification systems.
Key Concepts
- →Darwin's theory of natural selection: all species evolved from simple life forms over three billion years via natural selection acting on inherited variations.
- →Lamarck's hypothesis: changes that occur in an organism's lifetime ('acquired characteristics') are passed on to offspring, a concept now known to be biologically incorrect for inherited anatomical adaptations.
- →Reasons for slow acceptance of Darwin's theory: conflict with religious beliefs, insufficient fossil evidence at the time, and ignorance of the underlying mechanism of genetics/DNA.
- →Alfred Russel Wallace: independently proposed the theory of evolution by natural selection and worked with Darwin, also pioneering work on warning colouration and speciation.
Marking Points
- State that Lamarck's idea involved characteristics acquired during an organism's lifetime being passed to offspring.
- Explain that most acquired characteristics do not alter the DNA of gametes, so they cannot be inherited.
- Contrast this with inherited variation caused by mutations that produce new alleles in gametes.
- Use a correct example, such as a giraffe's stretched neck not being inherited, to show the idea is rejected.
- Recognise that inheritance depends on genetic material passed from parents to offspring, not on use or disuse of a body part.
Examiner Tips
- 💡Link the statement to a named scientist, such as Lamarck, so the examiner sees the historical context.
- 💡Use the phrase 'acquired characteristics' and explain why they are not usually passed on through gametes.
- 💡If asked to compare, set out one clear difference between Lamarck's idea and natural selection rather than listing many vague points.
- 💡Always state that survival leads to 'successful reproduction' and the passing on of 'alleles' or 'genes'—do not just say organisms 'survive and adapt'.
- 💡When explaining why Darwin's ideas were rejected, give distinct social and scientific reasons: religious objections, lack of fossil evidence, and unknown genetic mechanisms.
- 💡Remember to mention Alfred Russel Wallace if asked about the co-discovery of natural selection or early work on speciation.
Common Mistakes
- Thinking that any feature an organism develops in life is automatically inherited; correct this by stating that only changes in gamete DNA are normally inherited.
- Confusing Lamarck's idea with Darwin's natural selection; correct this by noting that Darwin's mechanism selects existing inherited variation rather than creating it by use.
- Writing that acquired characteristics are never inherited in any circumstance; correct this by saying they are not inherited in the vast majority of cases, leaving room for rare epigenetic effects.
- Believing organisms intentionally adapt or 'decide' to evolve in response to an environmental need, rather than selection acting on random pre-existing genetic variations.
- Assuming Darwin discovered genes and DNA; Gregor Mendel's work was only recognised later, and the structure of DNA was not solved until 1953 by Watson, Crick, and Franklin.
- Confusing Lamarck's acquired characteristics (such as muscle mass or stretched body parts) with heritable genetic mutations passed through gametes.
Revision Plan
- 1Day 1: Review Darwin's core principles of natural selection and practice writing the 4-step chain: mutation -> variation -> survival/reproduction -> allele passed on.
- 2Day 2: Compare Darwin's theory directly with Jean-Baptiste Lamarck's hypothesis of acquired characteristics using a comparison table.
- 3Day 3: Memorise the three specific historical reasons why Darwin's ideas were not accepted initially in 1859.
- 4Day 4: Study the contributions of Alfred Russel Wallace, specifically warning colouration and geographical isolation in speciation.
- 5Day 5: Complete past paper 4-mark and 6-mark questions on Darwin vs Lamarck and self-assess against official AQA mark schemes.
Exam Question Types
- 📋6-mark extended response comparing Darwin and Lamarck's explanations for an anatomical adaptation (e.g. neck length, webbed feet).
- 📋Short-answer questions (2-3 marks) asking for reasons why Darwin's theory was not accepted when first published.
- 📋Data analysis or source evaluation questions assessing how new evidence (e.g. fossils or DNA sequencing) supported Darwin's ideas over time.
Command Word Expectations (AQA)
Explain
Provide causes, mechanisms, or reasons. For natural selection, trace the cause from mutation to differential reproductive success and allele inheritance.
Compare
Identify both similarities and differences between two theories (e.g. Darwin vs Lamarck), rather than simply writing all you know about one followed by the other.
Evaluate
Review information or hypotheses, give points in favour and against, and reach a reasoned conclusion based on the scientific evidence provided.
How Students Lose Marks (Examiner Pitfalls)
Pitfall: Confusing Jean-Baptiste Lamarck's idea of acquired characteristics with Charles Darwin's theory of natural selection based on inherited genetic variation.
❌ Weak Answer (Loses Marks):Lamarck thought giraffes stretched their necks to reach tall trees and Darwin said giraffes just adapted to their environment over time.
Example improved answer:Lamarck proposed that changes occurring during an organism's lifetime through use or disuse are passed on to offspring (inheritance of acquired characteristics). In contrast, Darwin proposed that random mutations lead to phenotypic variation; organisms with phenotypes best suited to their environment are more likely to survive, reproduce, and pass on the advantageous alleles to their offspring.
Examiner Tip: Always specify that Darwinian selection operates on existing genetic variation produced by mutation, whereas Lamarckian evolution incorrectly relies on acquired characteristics being inherited.
Pitfall: Vague explanations for why Darwin's theory was not immediately accepted by the Victorian scientific and religious community.
❌ Weak Answer (Loses Marks):People did not believe Darwin because they were very religious and he did not have enough proof.
Example improved answer:Darwin's theory was only gradually accepted because: 1) It challenged the widespread religious belief that God created all animals and plants on Earth; 2) There was insufficient evidence at the time, particularly a lack of transitional fossils; and 3) The mechanism of inheritance and variation was not known because genes and genetics were not discovered until 50 years later.
Examiner Tip: Memorise the three distinct AQA mark scheme points for the slow acceptance of Darwin's theory: religion, lack of evidence/fossils, and unknown mechanism of genetics/inheritance.
Step-by-Step Worked Solutions
Question: Describe the theory of evolution by natural selection and explain why Darwin's ideas were not accepted by most scientists when first published in 1859. (6 marks)
- 1.Step 1: State the fundamental basis of Darwin's theory: individual organisms within a particular species show a wide range of phenotypic variation due to differences in their genes (mutations).
- 2.Step 2: Explain the mechanism of selection: individuals with characteristics most suited to the environment have a higher chance of survival and successful reproduction.
- 3.Step 3: State the inheritance mechanism: advantageous alleles/genes are passed on to the next generation over many generations.
- 4.Step 4: Detail reason 1 for slow acceptance: the theory conflicted with traditional religious beliefs that God created all living species individually.
- 5.Step 5: Detail reason 2 for slow acceptance: there was insufficient scientific evidence (e.g. gaps in the fossil record) at the time of publication.
- 6.Step 6: Detail reason 3 for slow acceptance: the mechanism of inheritance and variation was unknown because genes and DNA had not yet been discovered.
Final Answer: Darwin proposed that genetic variation exists within species due to mutations. Organisms with advantageous characteristics are more likely to survive and reproduce, passing these beneficial alleles to their offspring over successive generations. His theory faced resistance because it contradicted religious doctrines of divine creation, lacked sufficient transitional fossil evidence at the time, and could not explain the physical mechanism of inheritance since genes were discovered decades later.
Question: Explain how Jean-Baptiste Lamarck's theory of evolution differed from Charles Darwin's theory, using the evolution of long legs in wading birds as an example. (4 marks)
- 1.Step 1: Explain Lamarck's hypothesis: Lamarck proposed that an individual bird stretched its legs during its lifetime to stay above deep water, and these acquired longer legs were passed on to its offspring.
- 2.Step 2: Critique Lamarck's hypothesis: acquired characteristics cannot alter DNA/gametes and therefore cannot be passed on genetically.
- 3.Step 3: Explain Darwin's hypothesis: random mutations produced birds with natural variation in leg length.
- 4.Step 4: Conclude with Darwinian selection: birds with alleles for longer legs could wade deeper, catch more food, survive, reproduce, and pass on these alleles to future generations.
Final Answer: Lamarck suggested that individual birds stretched their legs during their lifetime and passed on this acquired characteristic to their offspring. In contrast, Darwin's theory states that pre-existing genetic variation meant some birds naturally possessed longer legs; these individuals had a survival advantage, reproduced more successfully, and passed on the alleles for long legs to subsequent generations.
Active Recall Memory Test
What was the title and publication year of Charles Darwin's famous book on natural selection?
Key Fact: On the Origin of Species, published in 1859.
What did Jean-Baptiste Lamarck incorrectly propose as the mechanism for evolution?
Key Fact: The inheritance of acquired characteristics (changes that occur during an organism's lifetime are passed to its offspring).
Give three reasons why Darwin's theory was not immediately accepted by the scientific community.
Key Fact: Conflict with religious belief in divine creation, insufficient fossil evidence at the time, and the mechanism of inheritance/genetics was completely unknown.
Which scientist worked independently on natural selection and co-published with Darwin in 1858?
Key Fact: Alfred Russel Wallace.
Frequently Asked Questions
Why did people reject Darwin's theory when he first published it?
When Darwin published his theory in 1859, Victorian society was deeply religious and believed in the literal creation of all species by God. Furthermore, Darwin could not explain how traits were passed down because Gregor Mendel's work on genetics was not widely known, and DNA was unknown. There were also notable gaps in the fossil record, meaning empirical proof was incomplete.
What is the key difference between Darwin and Lamarck's theories?
Lamarck argued that an organism's physical efforts during its lifetime changed its body, and these acquired characteristics were passed down (for example, stretching a neck made it longer). Darwin proved that natural variation already exists within a population due to mutations. Organisms possessing advantageous variations are more likely to survive, reproduce, and pass on their alleles.
Who was Alfred Russel Wallace and what did he do?
Alfred Russel Wallace was a British naturalist who independently formulated the theory of evolution by natural selection at the same time as Darwin. Wallace gathered extensive evidence in South America and Southeast Asia, prompted Darwin to publish 'On the Origin of Species' by sending him an essay, and pioneered the study of warning colouration and speciation.
Why is the theory of evolution considered a theory and not a law?
In science, a 'theory' is not a guess; it is an overarching, extensively tested explanatory framework supported by overwhelming evidence from multiple fields, including genetics, paleontology, and biochemistry. Laws typically describe mathematical relationships under specific conditions, whereas theories provide comprehensive explanations of natural phenomena.
Do I need to know about Lamarck for AQA GCSE Combined Science?
No. The historical comparison between Jean-Baptiste Lamarck and Charles Darwin, alongside the detailed reasons for the slow acceptance of natural selection, is exclusive to GCSE Biology (Separate/Triple Science) under specification section 4.6.3.1.