What went Wrong with Polygenism

I read that polygenism is pseudo-science, so I looked up some definitions:

Polygenism is a theory of human origins which posits the view that humans are of different origins (polygenesis).

Polygenism is the theory that the human races originated from multiple independent ancestral lines rather than descending from a common progenitor population.

So why is this wrong? Apparently because it competes with Out of Africa.

The Out of Africa theory is really two theories. The original Out of Africa I, which is considered disproved. And Out of Africa II, which is commonly accepted.

I found the explanations confusing and contradictory. Here is what I could figure out.

The human races did develop separately on separate continents, and racial differences are attributable to this separate development. To this extent, polygenism is true. Where it goes wrong is to say that human similarities are from convergent evolution. It is believed that those similarities are from common genes, as inherited from common ancestors.

Humans are believed to have descended from African apes who lived 5 million years ago. Out of Africa I said that all humans are direct descendants from Africans who migrated out 200K years ago. This cannot be right because of genetic evidence of interbreeding with European Neanderthals and Asian Denisovans.

Out of Africa II scales these claims back, and says that humans have mostly African ancestry, from a migration about 50K years ago. This is an attempt to salvage some of the Out of Africa I theory. Maybe 60% of your ancestry came from that migration, we do not know.

These theories are interesting to the extent that they help define what it means to be human, but they leave a lot of questions unanswered.

Africa appears to have had some apes walking upright, but those were not really human.

The main point of the Out of Africa theories was to explain (1) why humans have all the same potential; (2) why other human species like Neanderthals went extinct; and (3) why there has been no human evolution in the last 50K years. But all of this is now known to be false.

We still do not know why human ancestors evolved language and intelligence. It appears that Neanderthals evolved big brains about 1M years ago, long before the Out of Africa II migrations. And there appear to be some fossil gaps and population bottlenecks in the last 1M years. That may be when our ancestors became distinctly human.

We also do not know if it means anything to be mostly of African descent. The Neanderthal-African hybrids seemed to be more successful than either the Neanderthals or the Africans. So it is unknown which genes were more important.

Some people who write on this subject want to emphasize human similarities, and even similarities with apes. Others want to emphasize differences. We need both for an accurate scientific picture.