You should be patient; after all, it's hard to keep up with all those parts of evolutionary theory which have become discredited. Perhaps someone could post a link to a nice summary...
It was discredited by Darwin in 1859.
Back then, it was known from the fossil record that some kind of evolution (so-called "Law of faunal succession") had occured, it was just that no-one had any idea how it worked. Orthogenetic theory and Lamarckism proposed ad hoc explanations without any mechanism.
Then Darwin made the simple observation that the same mechanism that allows pigeon breeders to breed new breeds of pigeon is also at work in the natural world. He hypothesised that this accounts for all the diversity of life on earth.
He elevated this hypothesis to a theory by supporting it with lots of evidence, and by giving examples of how to falsify it.
Perhaps someone could post a link to a nice summary... Here's one