Still doesn’t make sense, surely a geneticist can look at rats and mice and document all the genetic differences between them.
Lets say for argument sake there are 100 total differences, and let’s say the argument you’re makings, is that there is this separate population of rats, each developed some of these traits individually, until the entire population gained all the traits over time and became mice. Surely, there is at one point, one individual member of the population that was the 1st to have all one hundred of these traits. That prior to that there were many with almost all of them, but none had all of them, until this individual mice came along.
There are not 100 total differences in genetics between rats and mice - there would be an AVERAGE difference between a typical mouse and a typical rat - different for each particular individuals you cared to compare.
If you invent iron clad criteria - you will often find nothing but disappointment when reality fails to comport well with the artificial criteria you invented.