Re: Bipedalism and theorizing... was Re: Morgan and creationists
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Fri, 26 Jul 1996 16:08:56 GMT
Paul Crowley <Paul@crowleyp.demon.co.uk> wrote:
>> I wouldn't be so sure about this.Clark and Tobias in their article
>> about the Sterkfontein footbones (Stw 573) write:"It is becoming clear
>> that Australopithecus was likely not an obligate biped,but rather a
>> facultative biped and climber.The exact proportion of its activities
>> spent on the ground and in the trees is at present indeterminate."
>What do you think they would have said if (assuming that they knew
>nothing of real chimps) they'd found a chimpanzee foot? Or a
>female/juvenile gorilla foot? My guess is that they'd have said
>"Here's a 100% arboreal animal".
Possibly,but the situation is artifical.
The fact is that they *do* know chimps and if they find a fossil of a
chimp foot then no one is going to say "100% arboreal" until at least
they've got remains of the upper limb too.It is only on the basis of
total morphological pattern that such a conclusion is justified.
But being mistaken even then is not impossible.We can only hope that
other data will correct us.
On the basis of comparative anatomy it is concluded that the
Australopithecines possessed an arboreal adaptive complex.It is
unlikely that such an adaptive complex would have been non-functional
and maintained for so long if it wasn't selected for.
The extent to which they were arboreal is uncertain though and may
have ranged from 10% to 50% or more.
It is premature to conclude that they must have been more terrestrial
than modern chimps since modern chimps may not represent the ancestral
locomotory condition.As terrestrial knuckle-walkers they are possibly
too derived.
>Bones are only a good guide to lifestyle or niche if you can compare them with close relatives
>whose actual niche is known.
And the conclusion is that Australopithecines had a unique niche that
was different from modern chimps.
>Predation generates great interest and excitement. AFAIR males get
>10% of the diet from it. They would certainly snatch a baby from an
>australopithecine female if they found her unprotected by a group.
>In spite of the fear inspired in them by modern hss, they have
>snatched babies in the Gombe area in recent times.
Goodall reports only two cases prior to her arrival as a researcher at
Gombe.That's not significant number from the point of view of
population dynamics.
In "The Chimpanzees of Gombe" (p.233) you can see that the total
consumption of meat by chimps never exceeds 10% of the diet in any
month and is much less most of the time.
At Gombe 80% of the prey species consists of Red Colobus,an animal
that is much smaller than an australopithecine.
So,I don't think that even if they were sympatric,predation on
australopithecines by chimps would have been significant.
>> Predation pressure by chimps also implies extensive sympatry,which may
>> not have been the case.
>Sympatry has to be assumed, especially since the recent finding near
>Lake Chad.
You may assume sympatry when fossils of different species are found in
the same strata and at the same location.
The finding (KT 12/H1,a partial mandible) you are refering to was not
found near Lake Chad but quite some distance northeast of it near Bahr
el Ghazal.
The associated fauna shows closest resemblances to that from Hadar
(with no chimps).The paleontological and sedimentological data are
described as being "compatible with a likeside environment,with both
perrenial and permanent streams,and a vegetational mosaic of gallery
forest and wooded savannah with open grassy patches".
The associated fauna consists of a.o.
Proboscidea,Giraffidae,Perissodactyla,Crocodilia.Doesn't look like
chimp habitat.
(Brunet,M.et al.(1995),The first australopithecine 2,500 kilometres
west of the Rift Valley (Chad),Nature 378:273-275)
>I doubt if we need to go deep here. Hss infants could not possibly
>develop any significant predator-avoidance behaviour or other useful
>activity in their early years. There is no purpose in having early
>development of the neuromuscular system prior to language and some
>cognitive awareness. The little that exists is usually dangerous.
This wasn't about predator-avoidance behaviour but about development
of motorbehaviour in relation to clinging.
Surely development of the neuromuscular system is important in
relation to this,because motorbehaviour ultimately depends on it.
If the infant has a delayed development of the neuromuscular system it
is likely that it cannot hold on to its mother shortly after birth.
Simply stating that human infants take longer to learn certain
motorbehaviours only touches the surface.
>OTOH, infant chimps need to able to avoid predators (especially
>dangerous males of their own species); when quite young they can get
>their food; in fact, they can get fruit further out on small branches
>that bigger chimps can't reach. If such early development was an
>advantage to hss, I'm sure it would be there.
It may have been impossible because its brain was not ready for it at
an early age.Nevertheless this disadvantage was apparently more than
compensated for by the advantages of a big brain later in
life,otherwise natural selection would not have let it pass.
>You've picked a case that makes my point. Why were those bare
>patches on Spindle's loins unusual? -- Because he was male.
>Goodall relates how exactly the same happened to another young
>male, Pax, when he later adopted Mel. You never see bare patches
>on females, neither on the loins nor where the infant's hands hold
>on. It's probably because female chimps have shorter body hair, or
>it may be the different shape of their loins or (unlikely) they may
>have tougher skin at those points.
Nevertheless is shows that the infant holds on to the hair.It is
possible that the sexual difference was selected for,since male
chimpanzees do not normally carry infants.
>Anyhow, take a good look at the picture of Spindle carrying Mel.
>Do you really think that there is the remotest possibility that
>Spindle would adopt a bipedal stance while carrying Mel? -- Or
>decide to carry him while walking bipedally for a few miles?
Not for a few miles,but that's because he is a modern knuckle-walking
chimp,not an ancestral hominid.
But just turn the picture 90 deg. and imagine Spindle climbing up a
treetrunk as they so often do while carrying an infant.Why should it
suddenly become physically impossible for the infant to hold on?
And what makes it physically impossible when the direction of movement
is horizontal instead of vertical?
>All other primates use the ventral position and it was, of course,
>the ancestral one. At the point of hominid speciation either one
>of two things happened: (a) the proto-hominid female did what you
>suggest; OR (b) the proto-hominid female first put the child down
>and then straightened up her back. Which is most likely?
If there are no physical objections,retention of the ancestral
condition until secondary altriciality evolves.
Gerrit.
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