after using the arrows on the top left in the best creature screen to look through past generations, i've discovered that the fastest creature has been bouncing back and forth from avg speeds of about 12 m/s to about 13 m/s and hasn't ever reached anything higher. i don't know how the fastest creature for one generation could possibly be slower than the previous because i have the "keep fastest creature for next gen" on. it's really weird. I don't think my "Muscle Beasts" can evolve any further. They should be but it's just not working right
edit: after looking through past generations i discovered it has been going from about 11 m/s to 13 m/s for hundreds of generations
edit: it actually got to 14 m/s at some points
edit: ok so they've been like that for over 2000 generations lol