Why are certain traits adaptations in one environment but not another
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An adaptation must fit the environment
Different environments require different skills and abilities to survive there. For example elephants' ears have a lot of surface area, and elephant skin is exposed with relatively little hair. These features are adaptations in their hot environments where they need to give off heat and cool down, but elephants would not be adaptations in very cold, arctic environments where they would need to retain heat. Same applies for fish as they can live inside water but if they are forced to live in earth they cannot live there because they cannot adapt the environment.
Answer:
Adaptation must fit the environment.
Explanation:
Adaptations are the behavioral, structural or functional modifications exhibited by living beings to make themselves better fitted in their respective habitat. Since different habitats have different environmental conditions, certain trait can serve as adaptations in one environment but not another.
Example: Reduction of leaves into spines is adaptive feature in dry environment to reduce the water loss. But it is not desirable in tropical environmental conditions where ample of water is available.