The extra "souls" are produced by the Wathan generators emplaced by the Ethicals.
This makes no sense. And I read the entire Riverworld series!
The assumption is that a person can be born who doesn't have a soul. There would have to be 'androids' who were born without souls before the Watham generator was constructed on a planet.
A 'android' would talk and act like a real person, but not have true 'consciousness' or 'feeling'. Everything they did would be a mechanical response. The Watham generator could modulate that response by giving the organism 'free will'. However, the soul would not affect the responses of the body and brain that evolved by natural selection. The main thing the Watham generator would do is give the response 'meaning'.
The first Watham generator was build by an android scientist who accidentally infused new souls into the newborns of his or her or its planet. The scientist himself never had a soul and neither did his contemporaries.
Everyone on a planet only has a soul if the Watham generator can keep up with the birthrate. However, the Watham generator can not determine the birthrate. If the Watham generator is not sufficiently productive for some reason, there will be those born without souls.
This in fact occurred on Riverworld because the Riverworld does not have a Watham generator. It has a computer that stores souls but not a generator that makes souls. When a body was resurrected, a soul was provided by the master computer. However, these souls had already been manufactured by the Watham generators planted on Earth before it was destroyed.
Or was the earth destroyed? Farmer said so early in the series through Monet. However, Monet turned out to be an undercover Ethical. So his story may have been a fabrication for his cover. This is n't relevant to the thread, however.
People were given birth control medication in their rations. However, some people resurrected in the Tower figured it out. Read 'Gods of River World'. They refused the medication. The result was that infants were born without souls. However, there would have been even more if the people on the Riverbanks had avoided birth control.
The salient point for this thread is the following. A shortage of souls would not reduce the birth rate on earth. Infants would simply be born without souls. So the OP can't logically use a decrease in birth rate as evidence that the number of souls were running out.
It is just as possible that the young people don't have souls. The Millenials may be absolutely soul less. The Baby Boomers have absorbed all or most of the souls that were manufactured by the Watham generators. The Baby Boomers may be the only living generation with Soul!
The OP should be trying to determine methods of detecting souls. It could make a big difference in our entitlement programs. I would think that the Social Security program would gain a great deal from the OPs insights.
There could be problems when the Androids respond to the loss of entitlements. They could fight the older but souled generation. However, the older folk have drones now. We don't have to fight the Androids directly. We could just send explosive drones to eliminate the Android Young.
I forgot. Just where did Jose Farmer say that earth's Watham generator was located?