Evidence for evolution — AQA GCSE Combined Science
Test yourself on Evidence for evolution with AQA GCSE practice questions.
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Evidence for evolution explained
Evolution is the change in inherited characteristics of a population over many generations, driven by natural selection.
Read the full explanation
Fossils provide direct evidence: remains, impressions or preserved traces show organisms that lived long ago, and sequences of fossils in rock layers reveal gradual change over time. For example, fossil horse ancestors show increasing body size and changing teeth. Antibiotic resistance in bacteria provides evidence that can be observed in real time. When bacteria are exposed to an antibiotic, most die, but random mutations give a few individuals resistance. These survivors reproduce, passing on the resistance allele, so the resistant proportion of the population rises. This is natural selection in action, and it shows that populations, not individuals, evolve.
The theory of evolution by natural selection is now widely accepted.
Evolution by natural selection explains how species change over many generations. Individuals in a population vary because of differences in their genes. Competition for limited resources means some variants survive and reproduce more successfully than others. These survivors pass their advantageous alleles to offspring, so those characteristics become more common in the population over time. Darwin proposed this mechanism in the nineteenth century, but acceptance grew only as supporting evidence accumulated. Today the theory is widely accepted because many independent lines of evidence agree: the fossil record, the similarities between organisms, and observations of rapid evolution such as antibiotic resistance in bacteria. A concrete example is the peppered moth, whose colour distribution shifted as pollution changed tree bark colour.
Evidence for Darwin’s theory is now available as it has been shown that characteristics are passed on to offspring in genes. There is further evidence in the fossil record and the knowledge of how resistance to antibiotics evolves in bacteria.
Darwin lacked a mechanism for inheritance, but modern genetics shows that characteristics pass to offspring through genes. Alleles are inherited, and mutations create new alleles, so variation has a genetic basis. The fossil record shows simpler organisms in older rocks and more complex forms in newer rocks, and transitional fossils link groups. Antibiotic resistance in bacteria provides observable evidence: random mutations give some bacteria resistance, antibiotics kill non-resistant bacteria, and resistant bacteria survive and reproduce, so resistance spreads. Each piece of evidence supports the same conclusion: species change over time by natural selection. Together, genetics, fossils and antibiotic resistance make Darwin’s theory widely accepted.
Your focus
- Describe how fossils provide evidence that organisms have changed over time.
- Explain how antibiotic resistance in bacteria demonstrates natural selection.
- Compare the timescales and types of evidence provided by fossils and by antibiotic resistance.
Show all 9 objectives
- Describe how natural selection leads to evolution over generations.
- Explain why the theory of evolution by natural selection is widely accepted.
- Use a named example to illustrate natural selection.
- Explain how genes provide evidence for Darwin’s theory.
- Describe how the fossil record and antibiotic resistance support evolution.
- Apply the idea of natural selection to explain the spread of antibiotic resistance.
Evidence for evolution exam tips
Marking Points
- Define a fossil as the preserved remains or traces of an organism that lived long ago, found in rocks or other preserved material.
- Explain that fossils show changes in organisms over time, and that older rock layers generally contain older, simpler fossils.
- Describe antibiotic resistance as arising from random mutation, with resistant bacteria surviving and reproducing when the antibiotic is present.
- Explain that the resistant bacteria pass on the resistance allele, so the proportion of resistant bacteria in the population increases.
- Link both examples to natural selection: variation exists, selection pressures act, and advantageous alleles become more common over generations.
- Variation exists within a population because individuals have different alleles.
- Competition and environmental pressures mean some variants are more likely to survive and reproduce.
- Successful variants pass their advantageous alleles to offspring, so allele frequencies change over generations.
- The theory is widely accepted because multiple independent sources of evidence support it, not because of a single observation.
- Acceptance increased over time as new evidence, such as genetics and antibiotic resistance, confirmed predictions made by the theory.
- Genes are passed from parents to offspring, so characteristics are inherited.
- Mutations produce new alleles, providing the genetic variation on which natural selection acts.
- The fossil record shows changes in organisms over time and links between ancestral and modern forms.
- Antibiotic resistance evolves because resistant bacteria survive treatment and reproduce, increasing the proportion of resistant bacteria.
- These independent lines of evidence all support evolution by natural selection.
Examiner Tips
- 💡Use the full chain mutation, variation, selection, reproduction, inheritance when explaining antibiotic resistance.
- 💡Refer to rock layers or strata when describing how fossils show change over time.
- 💡State clearly that evidence supports evolution rather than proving a particular mechanism, and keep examples specific.
- 💡Use the phrase ‘survive and reproduce’ rather than just ‘survive’, because reproduction passes alleles on.
- 💡Link each point back to alleles or genes to show the genetic basis of natural selection.
- 💡When asked why a theory is accepted, refer to multiple types of evidence rather than one example.
- 💡Use the antibiotic resistance example to show evolution happening in real time.
- 💡State clearly that mutations are random and selection is not random.
- 💡Link each evidence type back to natural selection rather than describing it in isolation.
Common Mistakes
- Saying bacteria choose to become resistant: correct this by stating that resistance arises from random mutation before exposure to the antibiotic.
- Claiming an individual bacterium evolves: correct this by explaining that natural selection changes the allele frequencies in a population over generations.
- Treating fossils as only bones: correct this by including footprints, burrows, impressions and preserved traces as fossil evidence.
- Thinking individual organisms evolve during their lifetime; correction: populations evolve across generations as allele frequencies change.
- Believing that organisms choose to change or that need alone causes change; correction: variation arises randomly, and selection acts on existing variation.
- Assuming the theory is accepted because Darwin was famous; correction: acceptance depends on evidence that supports the mechanism.
- Saying bacteria ‘decide’ to become resistant; correction: resistance arises from random mutation before exposure to the antibiotic.
- Confusing the fossil record with a complete record; correction: it is incomplete but still shows patterns of change over time.
- Thinking genes were known in Darwin’s time; correction: Darwin lacked a mechanism of inheritance, and genetics later supplied it.