Demonstrate understanding of evolutionary processes leading to speciation
What this domain tests
This domain assesses evolutionary processes that lead to speciation. You need to explain variation, selection, gene flow, genetic drift, reproductive isolation, and the difference between allopatric and sympatric speciation.
Core rules and concepts
- Variation arises from mutation and recombination; it is the raw material for selection.
- Natural selection changes allele frequencies when individuals with certain inherited traits survive and reproduce more successfully in a given environment.
- Gene flow moves alleles between populations; it reduces divergence.
- Genetic drift is random change in allele frequency, especially in small populations. The founder effect and bottleneck effect are examples.
- Speciation occurs when populations become reproductively isolated. Allopatric speciation involves geographic separation; sympatric speciation occurs without geographic separation, often through polyploidy or ecological isolation.
- Reproductive isolating mechanisms can be prezygotic (habitat, timing, behaviour, gamete incompatibility) or postzygotic (hybrid inviability, hybrid sterility).
Worked example
A river changes course and separates a lizard population. The two populations experience different climates and food sources. Over many generations, different alleles are selected, and mutations accumulate independently. If the populations meet again but do not interbreed successfully because mating behaviour and body size differ, reproductive isolation has occurred. This is allopatric speciation.
Traps that cost marks
Using Lamarckian need to adapt explanations; confusing speciation with extinction; saying drift is selection; ignoring reproductive isolation as the key criterion.