Evolution and speciation
Evolution
- Evolution is the slow formation of new species from earlier ones.
- It happens as the gene pool (all the alleles in a population) changes over generations.
- New species form when populations become genetically isolated.
Practice
Evolution is best described as:
Evolution is the change in a population's gene pool over time, which can lead to new species.
Evidence from DNA
- DNA sequence data shows how closely two species are related.
- The more similar their DNA, the more recently they shared a common ancestor.
Practice
Two species with very similar DNA sequences:
The more similar the DNA, the more recently the species shared a common ancestor.
Speciation
- Speciation happens when two populations become genetically separated, so they can no longer breed together. Two ways:
- allopatric speciation — populations kept apart by a geographical barrier (a sea, a mountain range).
- sympatric speciation — populations in the same area, separated by differences in behaviour or way of life.
Practice
Allopatric speciation requires:
Allopatric speciation needs a physical barrier (sea, mountains); sympatric happens in the same area via behaviour.
Practice
Speciation occurs when two populations:
Speciation is genetic isolation: the populations can no longer interbreed, forming separate species.
You've got it
Key idea
- evolution = the gene pool changing over generations → new species
- DNA similarity shows relatedness (more similar → more recent common ancestor)
- speciation = genetic isolation so they can't interbreed
- allopatric (geographical barrier) vs sympatric (same area, behaviour)