What is Natural Selection?
Natural Selection is one of the mechanisms which drives evolution. It is popularly characterized as "survival of the fittest," though that is not always the most accurate description. It is the tendency for life forms which are best suited to their environments to have a better chance to reproduce than those that are not. For example, in a cold environment, an animal with lots of fur is more likely to reproduce than a bald animal, since the bald animals will die more quickly.
[ References: Wikipedia: Natural Selection ]