Which of the following is true of a population that is evolving by means of natural selection

For a population that is evolving through natural selection the Organisms best adapted to their environment have the highest fitness. As these organisims have adapted to their environment in the best means possible.

Evolution is the change in a population through genetic variation over time. Natural selection may be through (1) differential reproduction, that is, not all organisms are able to reproduce to their fullest capacity because nature cannot simply sustain it and (2) acquire genes, that is heredity.