GCSE Biology Evolution & Classification Notes
Evolution by natural selection explains the diversity of life. Advantageous variations become more common over generations as their carriers reproduce more.
Key concepts
- Natural selection
- Variation → competition → survival of the fittest → advantageous alleles passed on.
- Speciation
- Formation of a new species when populations are isolated and diverge until they can no longer interbreed to produce fertile offspring.
- Evidence for evolution
- Fossils, antibiotic resistance in bacteria and observed selection in the wild (e.g. peppered moth).
- Classification
- Grouping organisms — traditional (kingdom → species) and modern three-domain (bacteria, archaea, eukaryota).
- Mutation is the ultimate source of new variation.
- Antibiotic-resistant bacteria (e.g. MRSA) evolve rapidly under selection pressure from antibiotic use.
- Darwin's theory was controversial because it contradicted religious teaching and lacked knowledge of genetics.
Worked example
Explain how a population of bacteria becomes resistant to an antibiotic.
- 1Random mutation in a bacterium gives resistance to the antibiotic.
- 2Non-resistant bacteria are killed; the resistant one survives.
- 3It reproduces and passes on the resistance allele.
- 4Over time, the whole population is resistant.
Answer: Mutation → selection pressure → resistant survivors reproduce → resistant population.
Common mistakes
✗ Saying bacteria 'want' to become resistant.
✓ Mutations happen at random; selection then favours the resistant ones.
✗ Confusing evolution with individual change.
✓ Individuals do not evolve; populations do, over many generations.
✗ Missing the word 'fertile' in the definition of a species.
✓ Members of a species produce FERTILE offspring together.
Quick check
Try these, then reveal the answers.
What causes new variation?Reveal answer
Random mutations.
State the four stages of natural selection.Reveal answer
Variation, competition, survival of the fittest, inheritance.
Why did Darwin's theory take time to be accepted?Reveal answer
It challenged religious views and there was no genetic mechanism known at the time.
Exam tips
- Always structure natural selection answers as: variation → selection pressure → survival → reproduction → inheritance.
- For antibiotic resistance, name the pathogen (e.g. MRSA) for credit.
- Distinguish speciation clearly using the 'no fertile offspring' criterion.
Related practice
Practise this topic
Exam-style questions with instant Gradion feedback.
Flashcards
Quick-fire recall to lock in the key facts.
Worksheets
Printable practice you can work through offline.
Past papers
Full papers with examiner-grade marking.
Gradion
Ask for a step-by-step explanation any time.
All Biology
Every Biology topic across every exam board.
Related topics
Frequently asked questions
What is natural selection?+
The process by which organisms best suited to their environment survive and reproduce more, passing on advantageous alleles to the next generation.
How does classification help scientists?+
It groups organisms by shared features (and DNA), showing evolutionary relationships and helping identify unknown species.
Create a free account to practise evolution & classification with Gradion feedback
Try 5 questions now, get instant examiner-grade marking and ask the Gradion to explain anything. Free during our early launch period — no credit card required.