This is the Aquatic Ape hypothesis, which has been around for many years, and Elaine Morgan has been the main proponent of it. Personally I have long been attracted to the idea. The opponents of it say that she is being selective in her choice of evidences. But similar things were said about Wegener's continental drift ideas. I've not seen adequate answers to all the points she makes. Here she is in her own words:-http://www.ted.com/talks/elaine_morgan_says_we_evolved_from_aquatic_apes.html