If we are all the result of past accumulated Karma that would seemingly suggest that if you reverse the process back in time sufficiently, there would be a point in the past where we have no accumulated Karma. Thusly, would one assume a mind absent from accumulated conditioning is pure, and if so - why would a pure mind manifest ignorance leading to the accumulation of current Karma?
 
I am aware the Buddha said there is no discernible beginning in the Tipitika. This is more for fun / speculative purpose. 

Metta

Perhaps there's never been a beginning. There's always been mind. There's always been karma.

-or-

Maybe this goes against Dharma theory, but perhaps it is wrong to assume at "the beginning" of mind, it was pure. What if it was born into illusion? 

< insert metaphysical speculation noble silence here >