Evolution and Animal Behaviour
This domain combines evolutionary mechanisms with animal behaviour. Questions ask you to interpret evidence, calculate allele frequencies or classify behaviour as innate, learned or social.
Core rules
- Darwinian natural selection requires variation, heritability and differential reproductive success. Fitness is relative reproductive output.
- Evidence: fossils, homologous structures (same origin, different function), analogous structures (different origin, same function), vestigial organs, embryology and molecular comparisons.
- Population genetics: Hardy-Weinberg equilibrium assumes no mutation, no migration, no selection, random mating and a large population. Deviations indicate evolution. Genetic drift is random allele-frequency change, especially in small populations.
- Speciation: allopatric by geographic isolation and sympatric within the same area, for example by polyploidy; reproductive isolation is the key criterion.
- Behaviour: innate behaviour includes fixed action patterns triggered by sign stimuli; learned behaviour includes habituation, classical conditioning, operant conditioning and imprinting. Social behaviour includes altruism, kin selection and eusociality.
Worked example
In a population at Hardy-Weinberg equilibrium, 16% show a recessive phenotype. Reasoning: q squared = 0.16, so q = 0.4 and p = 0.6. Heterozygote frequency = 2pq = 2 x 0.6 x 0.4 = 0.48, or 48%. This assumes the recessive phenotype is expressed only in homozygotes.
Traps
Natural selection acts on phenotypes, not on need. Homologous and analogous structures are often confused. Imprinting occurs during a sensitive period. Altruism is explained by kin selection, not individual benefit. Hardy-Weinberg is a null model.