It's not an "absurd idea", it's an observed phenomenon called "descent with modifications".
Genetic mutations happen in every generation of every species.
Most mutations have no effect on the appearance or functions of an organism because they occur in regions sometimes referred to as "junk DNA".
And for perfectly adapted species, those mutations which do change an organism are almost invariably negative and are therefore weeded out of the gene-pool by "natural selection".
That's why many generations can pass by, with no obvious changes.
But when the environment itself changes (becoming cooler, warmer, wetter, dryer, a new predator, etc.), then some mutations will increase an individual's chance of survival and reproduction, and so the species can begin to evolve again.
So a new species arises (by definition) whenever two sub-species have been separated in different environments so long they no longer successfully interbreed.
And we can see this in the process of happening, amongst horses, donkeys & zebras, to pick just one example.
None of this is "nonsense", and there's no "belief" (in a religious sense) involved.
These are simply very careful scientific observations, confirmed through innumerable repetitions.
In short, they are facts.
annalex: "It all can be summed up in a short statement: the account of creation is inerrant; God created all things visible and invisible; Adam and Eve are our historical protoparents.
If one wants to squeeze God-directed evolution in that, he is free to do so.
If one does not want to believe in evolution, he is also free to do so.
If one wants to deny historicity of Adam and Eve, or believe in evolution NOT directed by God, he is no longer Catholic."
That is also more or less the teaching of most Protestant and Orthodox denominations -- by my estimate along with Catholics totaling 80% of all Christians.
"Youg earth", anti-evolution and really, anti-science, is a distinct minority doctrine, even among Christian churches.
Yes. That is the belief -- in the superstitious sense. No one has observed that, no one has reproduced that in a sufficiently complex species, no one has really explained how two birth defects on the same kind would occur in two specimens within the mating range, but we believe it anyway.
Evolution as a scientific proposition is junk.
Now, miracles happen. That God can make it so two turkeys of the opposite sex would spontaneously mutate into bald eagles, -- or, to that matter into sabertooth tigers, -- and live happily ever after, -- that I can believe because I am Christian who evidences miracles on a regular basis. Not because of some ape with a science degree who thought it up.