Final answer:
Natural selection requires variation in inherited traits, reproduction to pass on these traits, and advantageous traits that aid in survival and reproduction. Genetic mutations can introduce new traits and adaptations arise from genetic variations. An unchanging environment is not necessary for natural selection.
Step-by-step explanation:
In order for natural selection to occur, organisms must meet certain conditions. Firstly, there must be variation in inherited traits within a population. Without genetic variation, there would be no differential survival or reproduction based on these traits. Secondly, individuals must reproduce and pass on their traits to their offspring. If advantageous traits are to spread through a population, they must be heritable. Thirdly, these traits must provide some advantage in the environment, aiding survival or reproduction.
Genetic mutations can introduce new traits, and hence increase variation within a population. If a mutation results in an advantageous trait, it may become more common over generations through natural selection. Additionally, natural selection acts upon an organism's phenotype, which is the set of observable characteristics that result from the interaction of its genotype with the environment. Adaptations are the traits that allow an organism to survive and reproduce in its environment and can arise from these genetic variations.
Therefore, in summary, for natural selection to occur, organisms must possess advantageous traits (a), undergo genetic mutations occasionally to introduce new traits (b), and reproduce to pass on these traits (c). The environment does not need to be fixed and unchanging; in fact, changes in the environment can be a driving force in natural selection.