Evolution by Natural Selection
Get to grips with Evolution by Natural Selection for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Organisms best adapted to their environment survive, reproduce and pass on their alleles — the heart of Darwin's theory of natural selection.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.
The process depends on variation. Individuals within a species show variation because of differences in their genes. Those with characteristics best suited to the environment are more likely to survive, breed successfully, and pass on the genes for those characteristics.
Over many generations the beneficial characteristics become more common in the population. If two populations become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have formed two new species.
Revision notes
The steps of natural selection
Individuals show variation due to differences in their genes.
Those with characteristics best suited to the environment are more likely to survive. They breed successfully and pass on the genes for those characteristics. Over many generations, those characteristics become more common.
Writing a full answer
A complete answer needs the sequence: variation, survival advantage, reproduction, inheritance of the alleles, and change over many generations.
Missing any step usually loses marks. The phrase over many generations is important because evolution is not immediate.
Speciation
If two populations of a species become so different in phenotype that they can no longer interbreed to produce fertile offspring, two new species have formed.
This is the definition of speciation and is worth learning precisely.
Key points
- Evolution is change in inherited characteristics over time.
- Variation arises from differences in genes.
- Individuals better suited to the environment survive.
- Survivors breed and pass on their genes.
- Beneficial characteristics become more common over generations.
- Two species have formed when they can no longer interbreed.
Worked examples
Example 1
Describe how natural selection leads to evolution. [4 marks]
Model answer
Individuals within a species show variation because of differences in their genes (1 mark). Those with characteristics best suited to their environment are more likely to survive (1 mark) and breed successfully, passing on the genes for those characteristics to their offspring (1 mark). Over many generations these characteristics become more common in the population (1 mark).
Example 2
Explain what is meant by a new species having formed. [2 marks]
Model answer
Two populations have become so different in phenotype (1 mark) that they can no longer interbreed to produce fertile offspring (1 mark).
Example 3
Explain why evolution takes many generations. [2 marks]
Model answer
The frequency of a beneficial allele increases only gradually, because each generation only slightly more individuals carry it (1 mark). It therefore takes many generations for the characteristic to become common in the population (1 mark).
Common mistakes
Saying individuals evolve.
Populations evolve over generations; individuals do not change during their lifetime.
Saying organisms adapt because they need to.
Variation is random. Natural selection then favours those already better suited.
Missing the reproduction step.
Surviving is not enough; the individual must breed and pass on the genes.
Forgetting over many generations.
It is usually worth a mark and shows understanding of the timescale.
Exam tips
- Learn the four steps and write them in order.
- Always include the passing on of genes.
- Use the phrase over many generations.
- Define a species by the ability to produce fertile offspring.
Key terms
- Natural selection
- The process by which better-suited individuals survive and reproduce.
- Evolution
- The change in inherited characteristics of a population over time.
- Species
- A group able to interbreed to produce fertile offspring.
- Adaptation
- A characteristic making an organism better suited to its environment.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.