When similar environmental pressures, such as permafrost in low-altitude tundra and permafrost in high-altitude alpine tundra, cause genetically distantly related organisms to evolve similar structures for survival and reproduction under similar conditions, has occurred.

Convergent evolution has occurred.

Explanation:

"Convergent evolution is the process in which organisms that are not closely related independently evolve similar features. Adaptions may take the form of similar body forms, colors, organs and other adaptions which make up the organism’s phenotype."

Reference: Editors, BD. “Convergent Evolution.” Biology Dictionary, 28 Apr. 2017

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