Amos said:

I expect "the total number of soul-driven organisms in existence from yesterday back to the big bang" is FAR greater a number than "the total number of soul-driven organisms on this planet today". If so, there is a huge SURPLUS, not scarcity, of souls capable of driving an organism ar one or another level of the complexity hierarchy.

Amos, I think you're missing something there (assuming I understand what you said). When a soul is reincarnated (assigned to another body after the death of the previous host) there is no net increase. So when the soul of Ughh, the caveman, was reborn as Urgha, the cavewoman, that soul would no longer be available until Urgha's demise. As that soul comes progressively down the line of beings, to become Uncle DaveO today, we'll say, all of that previous line of beings is now unavailable as a source of souls. Only after I kick off is my soul available for reassignment.   

Put another way, Adam and Eve accounted for two souls. Where did Cain and Abel get theirs, since Adam and Eve were still using what they had until their death a long time later?

If indeed there are souls, independent of bodies but attached to persons during earthly life, there has to be a continuous supply of new souls to keep the process going.

Dave Oesterreich