Natural Selection and Evolution

Natural selection is the mechanism by which evolution occurs. It was proposed independently by Charles Darwin and Alfred Russel Wallace in 1858 and remains one of the most important unifying concepts in biology. For A-Level Biology, you need to understand the process in detail, distinguish between different types of selection, and explain how selection leads to adaptation and evolution.

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Charles Darwin and the Theory of Natural Selection

Darwin's Observations

Charles Darwin developed his theory after years of observation, most famously during his voyage on HMS Beagle (1831–1836). His key observations were:

1. Overproduction — Organisms produce far more offspring than can survive to reproduce
2. Variation — Individuals within a population show variation in their characteristics
3. Struggle for existence — Resources (food, space, mates) are limited, so individuals must compete
4. Survival of the fittest — Individuals with characteristics better suited to their environment are more likely to survive and reproduce
5. Inheritance — Advantageous characteristics are passed to offspring, becoming more common in the population over generations

The Modern Understanding

Darwin did not know the mechanism of inheritance (he predated Mendel's work on genetics). We now understand that: