Changelings are not truly counted as one of the races in their own right due to how rare they are.
Those with the changelings traits are typically produced when denizens of the Feywild couple with those on Roshar. Sometimes this may be due to blessings, or curses, placed on persons and bloodline. Oftentimes the true origin of the changeling appearing is unknown.
Changelings differ from what others collectively refer to Shapechangers due to their lack of an “original form”. Upon death a changeling will not revert immediately to a particular form, such as a Doppelganger will, but will instead slowly revert at around the same rate as decomposition. The changeling will revert to what they would often term their “natural form”.
The natural form for a changeling is the form which a changeling would subconsciously assume, and scholars hold to reflect their own self actualised image. Due to this theory, scholars hold that a changelings natural form may vary drastically over time, particularly should the individual experience significant or traumatic changes in their life.