In https://www.upf.edu/cexs/news/genetica.html we find the following quote:
What also became clear to the researchers was the complexity of the evolutionary history of chimpanzees in comparison with humans. The patterns of genetic diversity were consistent with a vast genetic flux or migration between ancestral populations with sudden expansions in population size, followed by accidents.
"Humans", conversely, "have a relatively simple evolutionary history", say the authors. "It is clear that in the last few million years chimpanzee populations fluctuated enormously in size and complexity." The basis of these population collapses is clear but it coincides, in part, with a period of time in which the human population began to prosper.