Aquatic Ape theory?

I took a semester of Physical Anthropology and read one of Mogans books. It was interesting but unfounded. The Savannah theory from what I remember was that the drastic climatic changes caused the Jungles to recede which in turn opened up enormous grasslands and a new niche to exploit. Early arboreal apes began to frequent these grassland and through the process of mutation and natural selection and tremendous amounts of time, evolved into bipedal apes. I just compressed this theory into a paragraph but thats the jist of it as far as I can remember, Forum members feel free to correct me.