Evolution and Biodiversity
What you must understand
Evolution is the change in allele frequencies in populations over time. Know the evidence for evolution: fossils, comparative anatomy (homologous and analogous structures), embryology, and molecular biology (DNA and protein similarities). Understand Darwin's theory of natural selection: variation, inheritance, differential survival and reproduction, and adaptation. Know the difference between homologous structures (same origin, different function) and analogous structures (different origin, same function). Understand speciation (geographic isolation leading to reproductive isolation), the concept of a species, and the levels of biodiversity (genetic, species, ecosystem). Know classification: binomial nomenclature and the hierarchy (kingdom, phylum, class, order, family, genus, species).
Traps that appear in questions
- Confusing homologous (same origin) with analogous (same function) structures.
- Saying evolution is directed or goal-oriented - it is not.
- Confusing natural selection (a mechanism) with evolution (the result).
- Thinking individuals evolve - populations evolve, not individuals.
- Mixing up the order of taxonomic ranks.
Worked example
The wings of birds and insects both allow flight but arise from different origins - they are analogous structures, evidence of convergent evolution. The forelimbs of humans, whales and bats share the same bone plan - they are homologous, evidence of common ancestry. Rule of thumb: ask about origin, not function.