I tend to believe what really, really clever people have researched and offered proof and evidence for.
So you are willing to place your faith in anothers research on the basis that " these ones " appear to be clever.
How would you define intelligence?
There never has been conclusive evidence presented to show cross-species evolution and to say that there wouldn't be because this process may take millions of years is a fine theory, but hardly objectively proven.
I would suggest that you do not take for granted everything the secular rationalists say as absolute.