From Populations To Species
- When populations of the same species become geographically or reproductively isolated, they start to accumulate:
- Genetic differences through mutation and genetic drift
- Phenotypic differences through natural selection
- Over time, these differences may result in reproductive isolation, the key step in speciation.
More on speciation in A4.1.6.
The Gray Area in Classification
- In many cases, it is difficult to decide when diverging populations have become distinct species.
- Populations may not interbreed simply because they live apart, not because they can’t.
- If separated populations remain genetically and phenotypically similar, they are still considered the same species.
- Over many generations, isolation allows mutations, selection, and drift to cause divergence in traits such as size, color, or behavior.
- Eventually, these changes may lead to complete reproductive isolation, producing two distinct species.
- Speciation is a process, not a single event.
- The point at which populations become separate species is therefore often subjective, and may be an arbitrary decision.
- How does a population differ from a species?
- What mechanisms cause populations to diverge over time?
- Why is it difficult to determine when two populations become distinct species?
