They have never been proven.

Drosophila - fruit fly mutants that died out due to mutations damaging them. This proves evolution doesn't happen and darwinism is wrong. Ian T. Taylor has an amazingly poignant quote about this matter in his book, "In the Minds of Men":

Experimentation with fruit flies began in the 1920s with
Thomas Hunt Morgan and today is still a minor "industry"
among researchers. The stubborn fruit fly has endured
every genetic indignity possible, but so far not one has
ever produced anything except another fruit fly.