Answer:
Variation, Inheritance, Selection, Time and adaptation.
Step-by-step explanation:
Variation : Some variation occur in the off spring in appearance and behavior.
Inheritance : These variation are consistently passed on from parent to offspring of next generation to become genetic trait of the species.
Selection : Differential survival and reproduction of these species.
Time and adaptation : These variations/ traits become common in the population. The result is a population that is better suited--better adapted--to some aspect of the environment than it was before.
Example : Legs once used for walking are modified for use as wings or flippers. Scales used for protection change colors to serve as camouflage.
Hope it helps..