A river separates a population of insects. Conditions differ on its two banks. After many generations, insects from opposite banks can mate, but their offspring are infertile. Insects from the same bank produce fertile offspring.
Which sequence best explains the observations?
Isolation prevented mating; environmental differences produced useful mutations; these mutations made every insect on each bank equally adapted.
Isolation caused infertility; environmental differences then selected variants; their descendants gradually acquired different inherited characteristics on each bank.
Isolation prevented mating; environmental differences altered adult bodies; these acquired alterations accumulated in descendants until their offspring became infertile.
Isolation prevented mating; different inherited variants had reproductive advantages; genetic differences accumulated until insects from opposite banks produced infertile offspring.
40 exam-style questions on AQA GCSE Biology 6.3 The development of understanding of genetics and evolution, covering 6.3.1 Theory of evolution, 6.3.2 Speciation, 6.3.3 The understanding of genetics, 6.3.4 Evidence for evolution, 6.3.5 Fossils, 6.3.6 Extinction, and 6.3.7 Resistant bacteria. Each one has a worked solution and a mark scheme showing where the marks go.