Answer:
Variation. There must be variation in the traits of the individuals in the population, and some of this variation must be heritable, meaning it can be passed on to offspring.
Inheritance. The traits that vary among individuals must be encoded in the genes or have a genetic basis. Otherwise, they could not be inherited by the next generation.
Differential survival and reproduction. Individuals with certain traits must survive and reproduce more successfully than others in a given environment. This means that they have a higher fitness, or reproductive success, than others.
Time. Evolution by natural selection takes place over many generations. It is not a one-time event, but a gradual process of change in the population.
If these factors are present, then natural selection is likely to be the mechanism of evolution for that species. Natural selection causes populations to become adapted, or increasingly well-suited, to their environments over time2.
Step-by-step explanation: