2.1.2—Species definition
- Syllabus
- First assessment 2026
- Objective
- 2.1.2
- Level
- HL
Use Fertile Offspring as the Species Test
Under the biological species concept, members of one species can interbreed and produce fertile offspring.
Producing any offspring is not enough: fertility maintains gene flow between populations. The test is harder for fossils and asexual organisms, so other evidence may be needed.
Horses and donkeys can produce mules, but sterile mules do not maintain gene flow; horses and donkeys are classified as different species.
They fit the same biological species under this concept, assuming the populations can interbreed naturally.
Any offspring is not sufficient; fertility is the key condition.