Selective breeding... a
systematic breeding in order to change certain
qualities.
Thousands of years before Gregor Mendel discovered the magic that is genetics, people were picking and choosing plants and animals for certain traits.
A hen that laid fewer eggs than another would be killed. One that laid a few more would be put with the best rooster.
This carried on throughout the millenia as chickens laid more eggs, cattle produced more milk and flowers subtley changed in shades.
And techniques improved. Records of what had been bred to what were kept, genes were discovered and we learned that things like temperament can be genetic also, and in more recent years science has affected animals directly through cloning and gene splicing.