Not sure how much money to put on this gemome study, but it's all over the papers today.
Supposedly about 900 Ka for an extended period, the population ancestral to humanity (incl Nean and Denisovans) was drastically reduced to some 1300 individuals (probably some African refuge?). This coincided with the Early to Middle #Pleistocene transition with its big Ice Age oscillations, and may have led to evolution of a new species as common ancestor of us, Neanderthals and Denisovans (called H heidelbergensis here, but not everyone would agree with that).
https://www.nature.com/articles/d41586-023-02712-4