Predation, disease and competition for the means of survival result in differential survival and reproduction (natural selection)
Not every organism survives long enough to reproduce. Predators, disease, and competition for resources mean that individuals with helpful traits survive and breed more than others.
Real World
During the 1918 influenza pandemic, people with immune systems better able to recognise the H1N1 virus survived and reproduced at higher rates, shifting allele frequencies for immune-related genes in the surviving population.
Exam Focus
Always link the selection pressure to a specific phenotype advantage, then to reproductive success — three-step chains score full marks.
Evaluation Scaffold
A four-step framework for high-quality evaluation. Use this for 'assess', 'evaluate', and 'to what extent' questions.
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