Natural Selection
Natural selection is the mechanism behind adaptation, and it needs just three ingredients: individuals vary; some of that variation is heritable (passed on through genes); and some variants leave more offspring than others.[1] When those hold, any allele that improves survival or reproduction gets copied more often, so it spreads — no foresight required, just differential success compounding over generations. A mutation supplies the raw novelty; selection does the sorting. Even a slight, steady advantage sweeps a trait through a whole population surprisingly fast:
Even a small, steady advantage sweeps a trait through a population in a modest number of generations — the S-curve of natural selection. Bigger advantage or higher starting frequency → faster fixation.