Final answer:
Similar insulating skin coverings like fur in mammals and feathers in birds have evolved due to convergent evolution, where species independently develop similar traits to adapt to comparable environmental conditions.
Step-by-step explanation:
The evolution of similar insulating skin coverings such as fur, hair, and feathers in mammals and birds is a result of convergent evolution. This occurs when similar traits evolve independently in different species due to exposure to similar environmental conditions and selection pressures. For instance, both the arctic fox and the ptarmigan develop white coverings during winter to blend in with the snow and evade predators, despite one having fur and the other having feathers. This convergence is not due to a common ancestry; rather, it is the result of natural selection favoring characteristics that offer a survival advantage in similar environments.