Also what are they called?
remember the essential requirements for selection with the handy acronym V.I.S.T
V = Variation: All life forms vary genetically within a population. It is this genetic variation upon which selection works.
I = Inheritance: Genetic traits are inherited from parents and are passed on to offspring.
S = Selection: Organisms with traits that are favorable to their survival get to live and pass on their genes to the next generation.
T = Time: Evolution takes time. Evolution can happen in a few generations, but major change, such as speciation, often takes long periods of time.