Ring species are examples of species formation in progress. It's an illustration of one of the fundamental processes in evolution.
Thats a stretch... for an example of how scales became feathers.. How gills became lungs.. or even flowers became eggs.. The simplest explanation is probably the one most closely resembling the truth.. the Adam and Eve metaphor..
However Donkeys, Horses and Zebras may be related.. Metamorphosis is real.. but evolution may be a tall tale.. A yarn masked as Satans Gospel.. You know Satans gospel.. That God helps those that help themselves.. i.e. The Tree of the Knowledge of Good and Evil..