= Natural selection
{wiki}
<Natural selection> involves systematic differences in expected <reproductive success> associated with variation in <phenotype>. For a continuing evolutionary response, the relevant variation must be inherited: offspring must tend to preserve the differences being favored. Actual offspring counts also fluctuate by chance, producing <genetic drift>. Survival matters insofar as it affects contribution to future generations. <Genotype fitness> is therefore contextual, depending on environment and the life cycle being counted, rather than simply measuring strength or longevity. See https://openstax.org/books/biology-2e/pages/19-1-population-evolution[Clark, Douglas and Choi, Biology 2e: population evolution].
In chapter IV of his 1859 book, Darwin explained <natural selection> through preservation of favorable variations and greater chances of survival and reproduction. See https://darwin-online.org.uk/converted/published/1859_Origin_F373/1859_Origin_F373.html[Darwin, On the Origin of Species, first edition, chapter IV]. The beautiful consequence is cumulative change without foresight: inherited differences are filtered repeatedly by present conditions. <Natural selection> neither generates a needed <mutation> on demand nor guarantees progress toward a predetermined goal.
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