Writer and evolutionary theorist Elaine Morgan starts her TED talk by describing the ongoing paradigm: Chimps stayed in the trees and humans hit the savannas.
She argues that humans are just too different than the chimps to justify the ongoing paradigm–for instance, look at our naked (hairless) skin and bipedality. We didn’t evolve on savanna. Something else must of happened. She explains that there is a close connection between all of the naked animal species and water. Water life could also explain bipedality. Consider our distinctive layer of fat, which can’t be found in other primate species. Again, life in water would explain that layer in us (just like it explains that fat layer in whales). Consider also our speech. How is it that we can speak so well? Only the diving animals and diving birds have such incredible control of their breathing.
Morgan argues that it’s time to destroy the ongoing paradigm and declare that humans evolved in the water. According to Morgan, almost everybody likes the aquatic theory but almost everyone officially declares that it’s “rubbish.” But this is one of those cases where everyone could be wrong. She mentions David Attenborough and Daniel Dennett as recent converts to the aquatic ape theory.
[Note: some scholars have given detailed criticism of the aquatic ape hypothesis. For instance, see this entry at Wikipedia].
I've always been skeptical of the aquatic ape hypothesis because humans lack two basic adaptations that would be relatively easy to evolve and would present a huge advantage to an aquatic lifestyle: webbed hands and the ability to close our nostrils voluntarily.
I first heard of the aquatic theory in 1990 from Gonick's The Cartoon History of the Universe.
But a swamp-era makes more sense than a pure aquatic phase of our evolution. It better matches the now-known-to-be wet climate of the now-desert area where our earliest hominid ancestors have been found. Swamps also convey advantage to hairlessness and fat layers.
Ebonmuse: Modern Evolutionary theory states that environments select for advantageous traits. But environment does not apply pressure to create traits.
That's the essential difference between Darwin and modern evolution vs. Lamarck, Lysenko and their advocates such as Hitler and Stalin (all of whom spoke against Darwin's theories). Traits appear at random. Any new mutation may be fatal, advantageous, hampering, or neutral. Even beneficial traits can be weeded out by sexual selection or other social dynamics.
In the brief hypothetical aquatic or semi-aquatic phase of our evolution, only so many attributes may have appeared from which to be selected. Perhaps nimble fingers trumped webbing in a swamp, if it even manifested.
Here is a useful reference to anyone who wants to examine the data and ideas behind the Aquatic Ape theory: http://www.aquaticape.org