Complex sentence: He found that children of rats that had learned the maze were able to run it faster--the first rats would get it wrong 165 times before being able to run it perfectly each time, but after a few generations it was down to 20.
Split into simpler sentences: He found that children of rats that had learned the maze were able to run it faster. The first rats would get it wrong 165 times before being able to run it perfectly each time, but after a few generations it was down to 20.