The rodents’ vast litters incidentally offered up much raw material to the blind sculptors of natural selection; their evolutionary rate was ferociou… - Stephen Baxter

Superstition! A fatal flaw for a regime whose legitimacy comes entirely from religion.

It (i. e., agriculture) was the most profound revolution in hominid living since Homo erectus had left the forest and committed themselves to the savannah. Compared to this phase shift, the advances of the future—even genetic engineering—were details. There would never be so significant a change again, not until humans themselves disappeared from the planet.

Nothing mankind had done in its short and bloody history had made the slightest bit of difference to this patient geographical realignment.
Meanwhile the Earth, left to its own devices, had deployed a variety of healing mechanisms, physical, chemical, biological, and geological, to recover from the devastating interventions of its human inhabitants. Air pollutants had been broken up by sunlight and dispersed. Bog ore had absorbed much metallic waste. Vegetation had recolonized abandoned landscapes, roots breaking up concrete and asphalt, overgrowing ditches and canals. Erosion by wind and water had caused the final collapse of the last structures, washing it all into sand.
Meanwhile the relentless processes of variation and selection had worked to fill an empty world.