The development of understanding of genetics and evolution — AQA GCSE Combined Science: Trilogy
The evidence for evolution, how fossils form and what they show, evolutionary trees, extinction and antibiotic-resistant bacteria.
Revision notes
4 short notes, in the order of the specification. Each one in short:
The evidence for evolution by natural selection comes from three main sources. It has been shown that characteristics are passed on to offspring in genes. The fossil record shows how organisms have changed over time. Antibiotic resistance in bacteria shows natural selection happening in a short time. This evidence is why the theory is now widely accepted.
Fossils are the remains of organisms from millions of years ago, found in rocks. They form from parts of organisms that have not decayed, from parts replaced by minerals as they decay, or as preserved traces such as footprints and burrows. The fossil record is incomplete because many early life forms were soft-bodied and geological activity destroyed most traces.
Extinction occurs when there are no remaining individuals of a species still alive. Factors that may contribute include a change to the environment over geological time, new predators, new diseases, new, more successful competitors, and a single catastrophic event, such as a massive volcanic eruption or an asteroid collision. Each can reduce numbers until none are left.
Antibiotic-resistant bacteria are strains that are not killed by antibiotics, such as MRSA. Bacteria evolve rapidly because they reproduce at a fast rate. A mutation produces a resistant strain. When antibiotics are used, non-resistant bacteria are killed but resistant ones survive and reproduce, so the resistant strain spreads. Appropriate prescribing and completing the course of antibiotics slow this down.
Exam questions
3 exam-style questions (11 marks), each with its mark scheme.
Answer the questionsFlashcards
7 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of inheritance, variation and evolution on one page, so you can see where this subtopic fits.
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Quick check questions
Why is the fossil record incomplete?
Show answer
Early life was soft-bodied and left few traces, and many traces were destroyed by geological activity.
Why do resistant strains of bacteria spread so quickly?
Show answer
Bacteria reproduce quickly, people are not immune and there is no effective treatment.
Give one way to reduce the development of antibiotic resistance.
Show answer
Do not prescribe antibiotics inappropriately, complete the course, or restrict agricultural use.
Frequently asked questions
What is the evidence for evolution?
The evidence for evolution includes the fossil record, which shows how much or how little organisms have changed as life developed on Earth, the discovery that characteristics are passed on to offspring in genes, and antibiotic resistance in bacteria, which shows natural selection happening in a short time. This is why the theory is now widely accepted.
How are fossils formed?
Fossils form in three ways: from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent, from parts that are replaced by minerals as they decay, or as preserved traces such as footprints, burrows and rootlet traces. Fossils are found in rocks and show how organisms have changed.
How does antibiotic resistance develop in bacteria?
Antibiotic resistance develops by natural selection. A mutation produces a strain of bacteria that is resistant to antibiotics. When antibiotics are used, non-resistant bacteria are killed but the resistant bacteria survive and reproduce, so the resistant population rises. Because bacteria reproduce at a fast rate, resistant strains such as MRSA can spread quickly, with no effective treatment.
What causes a species to become extinct?
A species becomes extinct when there are no remaining individuals still alive. Causes include a change to the environment over geological time, new predators, new diseases, new, more successful competitors, and a single catastrophic event such as a massive volcanic eruption or an asteroid collision. Each factor can reduce numbers until none are left.
Written and checked against the AQA GCSE Combined Science (8464) specification · Updated October 2026