Evolution and Diversity of Organisms
Evolution and Diversity of Organisms
This domain tests natural selection, evidence for evolution, speciation, classification and binomial nomenclature. Questions often ask you to explain how a population changes over generations or to interpret allele frequencies.
Core rules
- Variation arises from mutation and sexual reproduction. Natural selection acts on phenotypes: individuals with inherited traits better suited to the environment survive and reproduce more, so allele frequencies change.
- Evidence includes fossils, homologous structures, embryology and molecular similarities. Homologous structures share ancestry; analogous structures share function but not ancestry.
- Speciation occurs when populations become reproductively isolated, often after geographic separation.
- Classification uses binomial names: genus capitalised, species lower case, both italicised. The five-kingdom system recognises Monera, Protista, Fungi, Plantae and Animalia. Viruses are acellular and not placed in these kingdoms.
Worked example
In a population, the dominant allele frequency p = 0.8 and recessive q = 0.2. Under Hardy–Weinberg, heterozygote frequency = 2pq = 2 × 0.8 × 0.2 = 0.32. In 500 individuals, expected heterozygotes = 0.32 × 500 = 160. Reasoning: p + q = 1 and genotype frequencies are p², 2pq and q².
Traps
Individuals do not evolve; populations do. Acquired characteristics are not inherited. 'Survival of the fittest' means differential reproductive success, not physical strength. Apes and humans are not descended from modern monkeys.