Hello Lang !
Thank you for your contribution.
Fascinating indeed. It is but a summary. Elaboration on the details can be found here and there all over the Site.
All is cause and effect. That includes kammic energy. An (over-) simplication, just for the purposes of my contribution here, would be: Avijja, abhisankhara, tanha, upadhana, javana citta (kammic energy) = hadaya vatthu + pasada rupa = bhava, jati etc.(that is composed of both ‘life’ and inert matter).
My own summary is: for any being, just like a circle, that sequence has no starting point throughout the beginningless past. That is what ‘Life’ is, in any of the 31 realms, along with the accompanying relative degree of suffering. But it can be brought to an end through the attainment of Arahanthood. Then it is an altogether different kind of ‘existence’ but with no suffering at all at any time, and forever. I have no other conception of Nibbana. But that does not matter for the time being. .