Even as a child watching the show, I always thought the Ed was not only special in that he could talk, but his brain must have been more highly developed from an ordinary horse, I mean he could talk about adult human concepts, problem solve, dial a telephone, work a TV, etc... pretty much anything Wilbur can do.

I always pictured a horse, or most any non-human animal to have the mind of a small child basically, so even if a horse could talk, there's no reason to think it could communicate effectively with a human and wouldn't just babble incoherent nonsense

I know it's just a show, but it would be interesting to know how Ed was so highly evolved

I think some animals are highly evolved. Mr. Ed is one of those. :)