Yes, that's one of the peculiarities. We human apes seem rather
better suited to an aquatic environment than most land mammals
(look how much money Californians spend on swimming pools, for
instance ;), and our closest relatives, the other apes, seem rather
less well suited to an aquatic environment than most land mammals.
Human beings also have a dive reflex built into the neurological
wiring that controls our breathing, similar to the dive reflex
found in pinnipeds, cetaceans, and other aquatic mammals. This dive
reflex (and voluntary control of the breath) seems to be missing
from our ape cousins, whose breathing seems to be as automatic and
involuntary as their heartbeat.
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.
FFI http://www.geocities.com/Athens/5168/aat.html, which is not
very academically oriented, but has the best available (that I
could find) single collection of links to a few sites and cites
that are academically oriented.
(And then there is the curious fact (?) that newborn human infants
know how to swim, and can apparently keep themselves alive without
difficulty in an aquatic environment, although the skill is lost
-- unless practiced? -- within a few weeks. I'm looking for further
recorded evidence of this. I have seen video footage of swimming
human infants, though.)
-- Eric Watt Forste ++ arkuat@pobox.com ++ expectation foils perception -pcd