Selection writes the fit
Heritable variation plus differential reproduction produces adaptation. This is natural selection.
Darwin and Wallace stated the mechanism in 1858. If offspring vary, if some of that variation is heritable, and if more are born than can survive, then traits that aid survival and reproduction become common. No foresight is required.
The modern synthesis added Mendelian genetics. We now watch selection in real time: antibiotic resistance, Darwin’s finches, experimental evolution in E. coli. The math of population genetics predicts the rates.
Selection is not the only evolutionary process. Drift, mutation, and migration matter, especially in small populations. They do not replace selection as the explanation of complex adaptation — eyes, wings, immune systems.
Caveats
- ‘Survival of the fittest’ is a slogan. Fitness is reproductive success in a given environment, not a moral ranking.
- Not every trait is an adaptation. Some are byproducts, some are drift.
Sources
- 1Darwin C., Wallace A. R.. On the Tendency of Species to form Varieties. Journal of the Proceedings of the Linnean Society, 1858.
- 2Fisher R. A.. The Genetical Theory of Natural Selection. Clarendon Press, 1930.