We've always been a manifestation of the physical - whether we were adams/atoms or not physical manifestation is what we are.
If you mean in the form that are currently in - the the answer is simple and not to complex -- EXPERIENCE.
Energy is neither lost or destroy - and that is what we are 100% energy. The first manifestation on this planet is as so-called black hue-mans -
Nevertheless, we always were and always will be - time-space travelers on every level coming in and out of different realities.
Peace
Ru2religious