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Problems with AAT (was Speech in H. erectus)
Joerg Rhiemeier (rhiemeir@ibr.cs.tu-bs.de)
11 Jul 1995 13:45:30 GMT
In article <herwin-0907952138020001@192.0.2.1>,
Harry Erwin (herwin@gmu.edu) wrote:
>I just finished browsing Tattersall, the Fossil Trail. He makes some very
>good arguments about the probable lack of speech in early H. erectus. In
>particular, he points out three features in the KNMER-15000 skeleton that
>suggest the Turkana Boy lacked language:
>1. The evidence of the small diameter spinal column that his chest lacked
>the detailed motor control that we have,
>2. The flat base of the skull indicating that there was insufficient room
>for a laryngial tract that could support complex language, and
>3. The conical chest shape (similar to that of Lucy and better adapted to
>climbing than our enlarged chest) that indicates he lacked chest volume.
>
>This told me a second thing as well--he probably was not good at holding
>his breath while swimming.
Things like this are what buggers me about the aquatic ape hypothesis.
It tries to explain several features of the modern human by
postulating a (semi-)aquatic stage some 4 to 7 million years ago,
completely ignoring that virtually all of these features did not
appear at that time, but only much later. Yes, Australopithecus did
walk upright, no doubt. But it neither had downward-facing nostrils,
and it was almost as hairy as a chimp, etc. p.p. Actually, it looks
like that all those `aquatic' adaptations did not occur until 200 000
or 100 000 years before present, at least not to the degree to be
found in modern humans.
This means that, if there was a (semi-)aquatic stage at all, it must
be put later, immediately before the advent of modern humans. So our
ancestors left their semi-aquatic habitat (I think the assumption of a
semi-aquatic habitat, like that of beavers, otters or some human
communities makes much more sense than a fully aquatic one) perhaps
100 000 years ago, but when did they enter it? Either the
semi-aquatic period was rather short, beginning perhaps 300 000 years
ago, or all those Homo habilis and Homo erectus types are not our
ancestors, but dead-end side branches just like Australopithecus
robustus or Homo neandertalensis.
Perhaps the stem population from which the different Australopithecus
and Homo species lived at the shoreline of an East African lake.
First they weren't particularly adapted to a semi-aquatic lifestyle,
just occasionally wading chest-deep (which would suffice for the
explanation of upright walking and subcutaneous fat, but not for
downward-facing nostrils, hairless skin, webs, diving reflex etc.).
Later they became swimmers and even divers. From time to time, things
happended to drive parts of the population away from the water. The
first of these dry land branches would have been the Australopithecus
genus, which left the watery habitat at an early, wading-only stage,
to be followed by at least two or three other emigrations, until
something finally drove the rest of the population out of
their original habitat 100 000 years ago (perhaps the lake dried out,
combined with a massive epidemy of tsetse flies). This could account
for the fact that the different Australopithecus and Homo species
display a gradual progression from the rather ape-like
Australopithecus to the `water-adapted' modern human.
If the semi-aquatic stage was rather short (from 300 000 to 100 000
years before now), the human evolutionary tree need not be rewritten,
as it only affects the last part of the path, after the split-off of
the Neandertaleans. If it was long (perhaps starting 5 million years
ago), the tree needs overhaul and must rather look like this:
H. sapiens (modern human)
/
0.1 million * H. neandertalensis(+)
years ago | / |
diving /? |?
| / |
| * H. erectus(+)
0.3 million |/ / |
years ago | ?/ |?
| / |
swimming / H. habilis(+)
| * /
1 million |/ /
years ago? | /
| /
| *
2 million |/ Australopithecus sp.(+)
years ago? | /
| / (possibly more than one branch from main line)
| /
| *
4 million |/
years ago? | Pan sp. (chimp, bonobo)
wading /
| / % Transition to semi-aquatic life
%? / * Departure from semi-aquatic life
6 million \ /
years ago | retreat of East African rain forest begins
(Perhaps the transition from wading to swimming was earlier.)
However, this semi-aquatic main line is so far not accounted for
paleontologically, such that a shorter semi-aquatic stage seems more likely.
Two side notes:
1.) It could be possible that the evolution of human language is
connected with aquatic lifestyle. In muddy water, where one cannot
see very far (especially with poorly adapted eyes, like ours), complex
acoustic signals are a very valuable means of communication. (Why
does no land-living mammal -- except humans -- have an acoustic
signalling and communication system as complex as the songs of
whales?) Language evolved when our ancestors started spending more
time diving, instead of just wading and swimming at the surface.
2.) Some people have objected that aquatic mammals like whales or
manatees have reduced hind-legs, while human legs are longer than those
of most apes. This argument completely misses the point. Loss of
hind-legs is a usual adaptation for a *fully* aquatic animal with a
strong tail and a fluke, but not for a *semi-*aquatic tailless
hominid. Most semi-aquatic vertebrates have normally developed
hind-legs, some even have especially strong ones (e.g. frogs; note
that they are tail-less! If our ancestors hadn't been forced out of
their lake, they might have evolved into something outwardly grossly
resembling huge frogs, if they had been given some million years more
time.)
--
~~o~~| Joerg Rhiemeier, Drosselstieg 4, D-38108 Braunschweig, Germany
~/V\~| phone: +49-531-376134, e-mail: rhiemeir@ibr.cs.tu-bs.de
~~H~~| Visit the World Wrights' Web! http://www.cs.tu-bs.de/~rhiemeir/
~/_\~| "A spirit with a vision is a dream with a mission." -- Rush
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