Describe the principles of natural and artificial selection?

Natural selection occurs when ecological pressures "select" for one trait over another. For example, if it is cold, an animal with a heavier coat will survive longer than one with a thin coat. The one with the heavy coat will have more offspring and that gene will be more frequent in the gene pool than the gene for a thin coat.

Artifical selection occurs when a desirable trait is selected and an undesirable one is not. For example, a long flowing coat on a dog may be more desirable to a breeder than a short, ragged coat. The breeder selects the genes.