Use fertile offspring to describe a species
Apply the syllabus species concept without treating appearance or individual infertility as decisive.
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Read the stated observations before choosing a group.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does fertile offspring mean?
What you will learn
- Describe a species using reproduction and fertile offspring.
- Recognise limitations of a single observation.
The outcome of reproduction matters
For the biological species description used here, organisms of one species can reproduce with one another and produce fertile offspring. Fertile means able to reproduce, not merely able to survive. Producing offspring that cannot themselves reproduce does not meet that criterion.
Organisms within a species can differ in appearance. Different dog breeds illustrate variation within a species; size or coat differences alone do not establish a different species.
Use the definition at the group level
An immature, old or infertile individual does not become a different species. The criterion concerns reproductive compatibility of the group, not a test that every pair must reproduce successfully in one attempt. A failed pairing alone has many possible explanations.
This biological species concept has limitations for asexual organisms and fossils. The syllabus description remains useful for the specified sexually reproducing examples, while other evidence is needed when its reproductive criterion cannot be applied.
Pause and explain
Which observation supports the same species under the stated concept?
Worked example
Two different-looking animal groups can interbreed and their offspring can also reproduce. What does this support?
Show the worked solution
- Check that offspring are produced.
- Check that the offspring are fertile.
- The observations support membership of the same species under this concept.
Answer They may be the same species despite appearance differences.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Groups X and Y produce offspring; those offspring produce a further generation. Interpret the evidence.
Give me a hint
Look beyond the first generation.
Compare my reasoning
- First-generation offspring exist.
- The further generation demonstrates fertility.
- The evidence supports the same species under the biological criterion.
Evidence supports the same species under the stated concept.
Look for these in your work
- Mention offspring fertility.
- Keep the conclusion tied to the criterion.
Two groups produce living but sterile offspring. Explain which part of the definition is unmet.
Give me a hint
Survival and reproduction are different abilities.
Compare my reasoning
- The hybrids survive.
- They cannot reproduce.
- Fertile offspring have not been produced.
The fertility requirement is unmet.
Look for these in your work
- Use sterile correctly.
- Avoid equating survival with fertility.
A museum has only fossil shells. Why can reproductive compatibility not be directly used to classify these specimens?
Give me a hint
What observation is impossible for fossils?
Compare my reasoning
- The organisms are no longer living.
- Their reproductive compatibility cannot be observed directly.
- Structural and other available evidence must be used.
The fertile-offspring criterion cannot be tested directly on fossil specimens.
Look for these in your work
- State the unavailable evidence.
- Suggest available structural evidence.
Common mistakes
- Viable offspring and fertile offspring are not identical ideas.
- Infertility of one individual does not redefine its species.
What can you explain now?
Two groups produce only sterile hybrids. Does that establish the same species under this criterion?
Compare with the explanation
No.
The offspring are not fertile, so the stated criterion is not met.
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Make it stick
State the species description, then give one situation where another type of evidence is needed.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.