Speciation
Get to grips with Speciation 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. A separate (triple) biology topic on how isolation and natural selection can drive two populations to become separate species, as proposed by Darwin and Wallace.
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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
Speciation is the formation of a new species. It occurs when two populations of the same species become so different that they can no longer interbreed to produce fertile offspring. This is a Triple-only topic.
The process begins with isolation. Two populations of a species become separated, perhaps by a geographical barrier such as a river or mountain range, so they can no longer interbreed.
Each population then experiences different environmental conditions, so natural selection favours different characteristics in each. Over many generations the two populations become increasingly different in phenotype, until eventually they can no longer interbreed to produce fertile offspring — two separate species.
Revision notes
Isolation
Two populations of the same species become separated, often by a geographical barrier such as a river, mountain range or sea.
Because they can no longer interbreed, genes are no longer exchanged between the two populations.
Different selection pressures
The two populations experience different environmental conditions.
Natural selection therefore favours different characteristics in each. Different alleles become more common in each population, and mutations arising in one are not shared with the other.
Becoming separate species
Over many generations the two populations become increasingly different in phenotype.
Eventually they are so different that they can no longer interbreed to produce fertile offspring. At that point two separate species have formed.
Key points
- Speciation is the formation of a new species.
- It begins with two populations becoming isolated.
- Isolation is often geographical.
- Different conditions cause different characteristics to be selected.
- The populations become increasingly different over generations.
- Two species exist when they can no longer produce fertile offspring.
Worked examples
Example 1
Define speciation. [2 marks]
Model answer
Speciation is the formation of a new species (1 mark), which occurs when two populations become so different in phenotype that they can no longer interbreed to produce fertile offspring (1 mark).
Example 2
Describe how a new species may form when a population is separated by a river. [4 marks]
Model answer
The river isolates the two populations so they can no longer interbreed (1 mark). Conditions on each side of the river are different, so natural selection favours different characteristics in each population (1 mark). Different alleles become more common in each population over many generations (1 mark). Eventually the two populations become so different that they can no longer interbreed to produce fertile offspring, so two species have formed (1 mark).
Example 3
Explain why isolation is necessary for speciation. [2 marks]
Model answer
If the populations could still interbreed, genes would continue to be exchanged between them (1 mark), so they would not become sufficiently different for two separate species to form (1 mark).
Common mistakes
Saying speciation happens quickly.
It takes many generations of gradual change.
Forgetting the word fertile.
Two species cannot interbreed to produce FERTILE offspring; some can produce infertile ones.
Omitting the isolation step.
Without isolation the populations continue exchanging genes and cannot diverge.
Saying the environment causes the mutations.
Mutations are random; the environment selects which are advantageous.
Exam tips
- Learn the sequence: isolation, different selection, divergence, no fertile offspring.
- Always include the word fertile in the definition.
- Explain why isolation matters if asked.
- Remember this is a Triple-only topic.
Key terms
- Speciation
- The formation of a new species.
- Isolation
- The separation of two populations so they cannot interbreed.
- Geographical barrier
- A physical feature separating two populations.
- Fertile offspring
- Offspring that are themselves able to reproduce.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.