Around 2000 I read a novel where one thread was about a far future where humans evolved into species with progressively less intelligence. The framing device for this thread was a small military team (one woman, two or three men) whose stasis device malfunctions and they awake in the far future. The first vignette the no-longer-humans were only slightly less intelligent than current humans, but the passage of time is shown by the team waking up from stasis to find that some but not all components of their clothing have disintegrated.
At one point there was some tension because one or more of the male team members expected the sole woman to have children with all of them to perpetuate the human species in this future. That was just in passing, I think, and at least one of the men had sex with the not-quite-human women.
I'm not sure why, but I think eventually the humans ran into a bad situation and triggered another round of stasis to escape. At which point the evolution of the no-longer humans had continued and they were even less like us...
One of the later vignettes had our no-longer-human primate descendants walking on all fours and being herded by intelligent rodents. "After all, there are worse fates than being herded by rodents."
The one-way time-travel vignettes were framed by chapters of "current" political and social dynamics which were less memorable, but dealt with (I think) social and ecological collapse.
It doesn't seem to be Timescape by Benford.