FWIW the populations weren't actually as small as a lot of these articles (including about human bottlenecks) allege in the popular press. This comes from a knowledge gap in the public compared to a biologists understanding here. The biologists are talking about effective population size (1) in most all these cases. This is an idealized sort of population size based on the idea of using the smallest possible population size that can fully capture the observed genetic diversity. It makes sense to use this measure, considering you are never fully sure how large a real population can be beyond its effective population size. So you just use the effective population size and implicitly acknowledge its assumptions.

This is well past HS biology though so popular press just skips that nuance and equates it to true population size.

https://en.wikipedia.org/wiki/Effective_population_size

There's new evidences that even Sapiens "introduction" in Europe happend multiple times in the scale of thousand years with migratory waves comming from Africa/Middle East.

There's a 12h Collège de France course from Jean-Jacques Hublin that display new understandings that is really captivating. It's in French though

I didn’t see it mentioned in the article, but I think it’s hard to fully appreciate how at risk they were to predators and that they were certainly not the top of the food chain yet. Humans and similar aren’t naturally adept for survival in the wilderness. We developed coping mechanisms but it took some time. Had to extinct a few big cats, bears, wolfs, etc along the way.

Why was this the case? I thought they were at least as intelligent as modern humans and had more muscle mass, used rudimentary tools and had control over fire. They lived in a climate without a lot of dangerous animals or a lot of disease and disease vectors at least compared to the jungles of Africa.