While all zebras have stripes, no two zebras share the same pattern. Variation, overpopulation or adaptation

Variation

Explanation:

"Overpopulation" describes an issue in which there are too many of a certain organism.

"Adaptation" describes a phenomena where an organism evolves to adapt in its environment.

Well, lets compare zebra stripes to fingerprints. Fingerprints have nothing to do with overpopulation, and unique fingerprint patterns have nothing to do with adaptation, but the seemingly infinite variation in both fingerprints and zebra stripes is definitely there. So, the uniqueness of the patterns throughout  each zebra individual is variation.