True, we cannot prove evolution, but nothing in science is provable, only disprovable. Science works on varying degrees of evidential support. Evolution happens to be one of the most supported scientific theories of all time. While evolution can never be proven, I do think we can be certain of it. Part of the confusion about evolution comes from the notion that evolution is both a fact and a theory. It is a fact that populations change over time (we can now directly observe this at the genetic level) and give rise to new species (
Observed Instances of Speciation). There's also the fossil record and genetic testing that creates the twin nested hierarchy; two separate lines of massive evidence that are parallel with each other and consistent/supporting evolutionary theory. The theory of evolution explains these facts and many more.
What is most striking about the clergy is that after the Clergy Letter Project was founded, a second project was undertaken as a response; the Creation Letter Project. The Creation Letter, started a few years ago, are signatures of clergy who reject evolution and accept creationism. What is really striking is that not even 300 signatures from Christian clergy could be collected in support of creationism. There are more than 40 times the amount of signatures for evolution than for creationism among Christian clergy! Just for another perspective, Judaism is literally about 0.2% of the world population where Christianity is a good 33%, and there are more signatures of Jewish scholars who accept evolution than there are of Christian clergy that reject it!
As for the Bible, both Christian and Judaic scholars, when using standard exegesis and hermeneutics, have concluded that Genesis is not meant to make any scientific claims about the world, this includes evolution. This analysis is held by scholars who do and don't accept evolution. Also, many Christians and most Jews view Genesis as metaphorical rather than a historical account (again supported by exegesis and hermeneutics). Essentially I am trying to say that for Christians who accept evolution, the Bible's message is true, however the creation accounts are not literally true.
I do think Catholics should be considered Christian and thus applied when doing statistics on Christianity. However if you want to exclude them, the majority of protestants also accept evolution. It isn't until you get into conservative circles do you see large numbers of creationists, and they just happen to be a vocal minority.
Red