unnatural selection
How have humans , elves , dwarves, and halflings, and orcs managed to survive the pressures of natural selection in the worlds of Golarion or Faerun ? There are hoards of beings at least as intelligent ( if not more ) as them but with far more adaptable qualities. Drow , githyanki, numerous shape shifting humanoids and colossal intelligent beings... giants, dragons... Even with ingenuity and perseverance , the evolutionary niche of the intelligent humanoids I mentioned is far outclassed by numerous fey, demons, devils, and hybrids. There's no place for the species. All should be at least fully hybridized by now with all the more adaptive available options for crossbreeding with dragons, demons, and angels. The level of diversity just doesn't make any sense. Not to mention the extra selection pressure from apex predators like tyrannosaurus rex, otyughs, drakes, etc.