Your assuming that evolution is a natural process that occurs. Sadly, there is no evidence or observed proof that anything has every turned from one animal into another.
The ‘by chance part’ applies to the idea of the very first organism that formed from primordial stew. Also, never has happened or never observed happening.
Sadly, there are literal mountains of evidence which some people studiously ignore & deny.
What that evidence shows is that most all evolution happens over long periods with many intermediate forms.
Sure, some people pretend there are no intermediate forms, but only by keeping their eyes tightly shut.