What is natural selection?

Natural selection is part of Charles Darwin's theory of evolution.
It is when a species adapts to changes in the environment, allowing them to survive. If natural selection doesn't favour a species, it will become extinct as it cannot survive in the environment.
It is the idea of the 'survival of the fittest' - meaning species who have evolved more useful adaptations, like webbed feet or camouflaged skin, are more likely to survive, breed and pass on their adaptations to their offspring.Eventually this adaptation will become more common in the gene pool, allowing the species to adapt and survive.