
Marisa F. answered 01/04/21
Award-winning College Professor
Natural Selection is 1 of the 4 forces of evolution that directs species adaptation to their physical environment. Natural Selection can only act on heritable traits that already exist within a species. That means that every variation of a specific trait that exists in a given species is either selected for or against inclusion in the next generation. The traits that give an individual that ability to survive long enough to reproduce & pass their traits on to fertile offspring are typically the traits with the highest fitness and therefore show up in the next generation as long as the trait is advantageous in the species' particular environment. Which ever variation of a trait confers the best fitness for the environment will be passed on until the environment changes. This is what is meant by survival of the fittest -- it's not the biggest, strongest, or fastest individuals that survive, but those who possess traits with the best fitness for their environment that survive.