>The Aquatic phase of human evolution, unfortunately, falls into
>the "Fossil Gap" that lies between Lucy (the first fully bipedal
>human ancestor, and apparently the immediate successor to the
>Aquatic Ape, if such a thing ever existed) and the earlier common
>ancestors of the modern pongid apes (including Homo), whose existence
>is almost as poorly documented in the fossil record as the existence
>of any hypothetical wading hominids is.
Well, the Aquatic Ape theory holds that. However, there's really no reason
the aquatic phase had to be then. The aquatic phase could have been between
Habilis and Erectus, or between Erectus and us. There could have been
multiple aquatic phases, for that matter. AAT wants to explain bipedalism
via an aquatic existence but that's hardly the only way to explain
bipedalism.
Indeed, the gracile bone structure that distinguishes us from other hominids
is rather a mystery, but if we were semi-aquatic and the other hominids
weren't, it would at least serve some purpose. We don't know whether other
hominids had any of the other purported aquatic adaptations, such as
hairlessness, sweating, subcutaneous fat, or a diving reflex; there's none
left. I understand there's evidence that Erectus was quite a runner, though,
and that would make one expect sweating at least.