Final answer:
Natural selection is a fundamental biological process where individuals with advantageous heritable traits are more likely to survive and reproduce, leading to those traits becoming more prevalent in the population over time.
Step-by-step explanation:
Natural selection is a critical mechanism of evolutionary change and occurs when individuals within a population have heritable traits that provide a selective advantage in their environment. For example, selective pressures such as predators, food scarcity, or mate selection can influence which individuals survive and reproduce. A phenotype that enhances an organism's ability to avoid predation, for instance, would likely increase that organism's viability and fecundity. It's important to note that successful traits need to be passed to offspring for natural selection to effect changes within a population. Over time, the favorable traits become more common in the population, leading to adaptive evolution.
Adaptive evolution, however, is constrained by existing genetic variance within the population and cannot create new traits from nothing. Mutation and gene flow can introduce new alleles, some of which may offer additional advantages or disadvantages under environmental selection. Traits that confer an advantage can lead to increased representation of the beneficial alleles in subsequent generations if the environmental conditions remain consistent. This results in an evolutionary change, shaping the population to be better adapted to their environment.