1. Random mutation, and then
If you don't buy into this inane tautology, then "you don't understand evolution. It's simply too complicated a branch of fake science for you.
There could not be thousands of papers, hundreds of books and videos and lectures challenging the archaic notion proposed by Darwin and earlier by others. "A new scientific truth does not advance by convincing its opponents, and making them see the light, but rather because its opponents eventually die." - Max Planck