Around genes there are areas that control their expression. Since their function is really important, scientists thought they would have few mutations. However, in the DNA of man and chimpanzee it has been proven that these areas have numerous harmful mutations. In contrast, in rat and rat regulators there is much less mutation.
It seems that the populations of rodents have crossed each other more, so the existence of mutations in regulators would have very negative effects. However, human and chimpanzee populations have not crossed so much, so the consequences of mutations have not been so serious.