Final answer:
Natural selection requires heritable variation in traits, differential reproductive success, and competition for resources. It does not require an inner need to evolve, a catastrophe, or an evolutionary goal.
Step-by-step explanation:
For natural selection to occur, certain conditions must be present in a population.
First, there must be heritable variation in traits among individuals. This variation is critical, as it provides the raw material upon which natural selection can act.
Secondly, individuals in the population must differ in terms of reproductive success; in other words, some individuals are more successful at leaving offspring than others.
Lastly, competition for resources often acts as a pressure for natural selection, as those with traits better adapted to their environment tend to have more offspring that survive to reproduce. It is not necessary for there to be an inner need to evolve, a catastrophe, or an evolutionary goal.