The Biological Species Concept (Modern Definition)
Definition
Biological Species Concept (BSC)
The biological species concept (BSC) defines a species as a group of organisms capable of interbreeding and producing fertile offspring, emphasizing reproductive isolation.
- This is the primary definition used in modern biology, unlike the morphological concept.
- This view focuses on reproductive compatibility and shared gene pools, not just appearance.
- Lions (Panthera leo) and tigers (Panthera tigris) are separate species because they do not interbreed in the wild.
- Hybrids like ligers (male lion × female tiger) are typically sterile, preventing gene flow.
Key Principles of the BSC
- Interbreeding ability: Members of the same species can mate and produce fertile offspring.
- Shared gene pool: All individuals exchange genes within the same population, maintaining genetic continuity and diversity.
- Reproductive isolation: Different species are separated by barriers, geographic, behavioral, physiological, or genetic, preventing gene flow and ensuring independent evolution.
Reproductive isolation is the mechanism that maintains distinct species boundaries.
When the BSC Cannot Be Applied
Other classification methods are used when reproductive isolation cannot be tested:
| Alternative Concept | Basis for Classification |
|---|---|
| Morphological | Observable physical traits |
| Genetic / Molecular | DNA or protein similarity |
| Ecological | Distinct ecological roles or niches |
| Evolutionary lineage | Ancestral relationships in fossils |
| Biochemical | Differences in metabolism or chemical pathways |
- No single definition fits all organisms.
- Species concepts are tools, chosen based on context and available evidence.
- What is the main definition of a species under the biological species concept?
- What role does reproductive isolation play in maintaining species boundaries?
- Why is this concept more consistent with evolutionary theory than the morphological one?
- Name two types of barriers that prevent interbreeding.
- Why can’t the BSC be applied to bacteria or fossils?
