Isn't the development of bipedalism and good hands prior to the
bigtime encephalization increase made at bit more explicable by
the Aquatic Ape theory that keeps showing up in the subject line
without being discussed much? Bipedalism would allow a broader
wading range (since presumably the duration of the aquatic clade
was too short for the development of true swimming adaptations such
as blubber and flippers), and good hands would be needed for
exploring muddy lakebeds for food. If this take on things is so,
then we would expect the aquatic clade to have existed sometime
shortly before afarensis (AKA Lucy)... sometime in the four to five
million years ago range.
If an earlier aquatic habitat accounts for many of Lucy's features,
then perhaps Calvin is right in that a post-Lucy stonethrowing ape
accounts for the later encephalization, *particularly* if Calvin
is right in claiming that stonethrowing adaptations are deeply
connected to the development of language, which is what vastly
accelerated cultural evolution.
Another puzzling piece of this puzzle is the molecular-clock stuff.
Last time I looked into this (admittedly a long time ago), I recall
someone arguing rather strenuously that the pongid radiation (chimps,
gorillas, and homo) could not have taken place more than three or
four million years ago. Since Lucy looks pretty solidly on the Homo
branch of that radiation (although evolution has done stranger
things than allow a clade of afarensis to "backslide" into chimps
and gorillas) I would guess that the estimated date for the pongid
radiation has been pushed back to before the time of the Lucy
fossils, but here I'm guessing. Would anyone like to elaborate on
any of these points?
-- Eric Watt Forste ++ arkuat@pobox.com ++ http://www.pobox.com/~arkuat/