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Part 1 — Darwin’s natural selection, its critics, and the modern synthesis that added genetics.
In this lesson you will
Charles Darwin (with Alfred Russel Wallace) proposed natural selection in On the Origin of Species (1859). Thomas Malthus had argued that populations grow geometrically while food grows only arithmetically, which led Darwin to the idea of a struggle for existence.
| Postulate | Meaning |
|---|---|
| Overproduction | Organisms produce far more offspring than can survive |
| Struggle for existence | Competition for limited food, space and mates (within and between species, and with the environment) |
| Variation | No two individuals are alike; many variations are inherited |
| Natural selection | Individuals with useful variations survive and reproduce more (survival of the fittest) |
| Origin of species | Useful variations accumulate over generations, giving new species |
Selection can be seen in nature and in human-made environments.
| Example | What happened |
|---|---|
| Industrial melanism (peppered moth, Biston betularia) | In industrial England, soot darkened tree trunks; light moths were eaten by birds and dark moths increased |
| Giraffe’s long neck | Darwin: giraffes with longer necks reached more leaves and left more young (not, as Lamarck said, by stretching) |
| DDT-resistant mosquitoes | Spraying killed sensitive insects; rare resistant ones survived and multiplied |
| Antibiotic-resistant bacteria | Antibiotics killed sensitive cells; resistant mutants spread |
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