Evolution

About this unit

Evolution explains how the diversity of life arose over very long periods of time. This unit covers ideas about the origin of life, including chemical evolution and Miller's experiment, and the evidence for evolution from fossils, comparative anatomy, embryology and observed changes such as industrial melanism. It then explains Darwin's theory of natural selection, adaptive radiation, the sources of variation, the Hardy–Weinberg principle and the story of plant, animal and human evolution through geological time.

Key ideas

• Life probably arose by chemical evolution from simple inorganic molecules.
• Homologous organs show divergent evolution; analogous organs show convergent evolution.
• Natural selection acts on heritable variation; fitness means reproductive success.
• Adaptive radiation produces many forms from one ancestor in a region (Darwin's finches).
• Gene flow, genetic drift, mutation, recombination and selection disturb Hardy–Weinberg equilibrium.
• Human evolution passed through Australopithecines, Homo habilis, Homo erectus, Neanderthals and Homo sapiens.

How to prepare

Make a table (in your notebook) of homologous and analogous examples. Practise Hardy–Weinberg calculations using p² + 2pq + q² = 1. Learn the sequence of hominid ancestors with brain sizes, and the three types of natural selection with graphs.