Work by Belén Mercader.
The Natural Selection is the term used in biology for the process by which biologic traits become more or less common in population due to consistent affects upon the survival or reproduction of their bearers.
The evolution is the result of the natural selection plus the changes in the environment.
The natural selection consists in the survival of the strongest, one example is the birds’ beak, if there is an environment in which the principal aliment are the nuts, those birds with the strongest beak will survive and they will be good fed, but the birds who haven’t got a strong enough beak, they will have a lack of food and the specie could not survive.
The first paragraph: es.wikipedia.com/wiki/natural_selction