This question is sure to open a massive can of worms. In my opinion, it's a theory that's not observable or provable. Which doesn't make it scientifically viable. Biologists have proven that it is a scientific impossibility for a reptilian DNA to mutate into bird DNA. Yes, species do adapt to environment and other pressures but never to the extent that they become another species. The scary thing is that they are teaching evolutionary theory to our kids as scientific fact. Therefore something that cannot be proven has to be taken as truth by faith. Sounds like religion to me, and I thought they didn't want that in the schools. Sounds like another agenda here.
All you need for something to sound plausible these days is just find someone who knows a heap of big words, put them together with some dodgy artwork and maybe a few titles behind their name and now you have scientific fact. Like I said, very scary.