Then it could also have "arisen independently" many hundreds and thousands of times and descended along many unrelated lines. That is not the theory of evolution as taught in the classroom.
To assume that the speciation of microscopic lifeforms proves that all species evolved from other species is a giant logical leap. It's a non-sequitur. It just does not follow that observing speciation proves that all species speciate, much less that all species are descended from one single common ancestor. The theory of evolution is built upon a mountain of such logical fallacies. For example, your argument appealing to the authority of the Pope does not help make the case that evolution is not a religious belief based entirely on faith and philosophic world-view.
This article sure seems to support that.
So species don't speciate - unless they do - and at many thousands of times the usual rate?
The evidence - of Endogenous Retrovirus - of gene families - of nested hierarchies of similarity in DNA - and others - all support the common descent of species.
Observing speciation doesn't mean that all species will speciate. That is correct. But any species that uses DNA will be subject to change. Change is inevitable. DNA replication itself causes change.
I am not appealing to the authority of the Pope that evolution is true - just that it is consistent with a faith in God. If you state something cannot be - that one cannot accept evolution and have faith in God - then it would be incumbent upon you to explain how the Pope and many other millions of Christians have no faith in God.
But that is a theological argument - if you want to argue the evidence - read up on endogenous retroviral sequences and get back to me.
When you have a basic understanding of the evidence then you might credibly argue the nature of the evidence.