Question

Over time, the variation that gives an Press enter key to drop response here.Response input area becomes more common in the population – Press enter key to drop response here.Response input area selection.
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Answer 1

Sounds like you're asking which process makes a beneficial variant become more common.

Answer: natural selection.

Briefly: if individuals vary for a heritable trait and one variant gives higher survival or reproduction, those individuals leave more offspring, so the advantageous variant increases in frequency over generations. When one extreme is favored and the population average shifts in that direction, this is called directional (or positive) selection.

Example: a mutation causing antibiotic resistance spreads in a bacterial population under antibiotic treatment.