Spiritual Explanation
According to indian history, There were
Hrishis &
Yogis 1000s of years B.C. Who were able to undergo spontaneous human combustion process with the power of
YOG ...Mahirshi Dadhichi is the best example of this process by which he converted his bones into a VAJRA through YOGA POWER which later on was used by demigod INDRA to defeat VRITRA ...
http://en.wikipedia.org/wiki/Dadhichi