Re: Bipedalism and theorizing... was Re: Morgan and creationists

22 Jul 1996 20:02:26 GMT

The following has been trimmed...

Gerrit Hanenburg ( wrote:
: Paul Crowley <> wrote:

: ---trimmed---

: >Walking or running with infant attached is a very different matter
: >from just sitting with one. It's absurd to say it's "just another
: >form of orthograde positional behaviour".

: But it *is* another form of orthograde positional behavior,meaning
: that it is positional behaviour in which the long axis of the body is
: more or less perpendicular to the horizontal plane,just like in
: brachiating,suspension and vertical climbing and leaping.
: In al these forms of orthograde positional behavior primate infants
: are able to cling,whether or not these movements are slow or fast.

Oxnard has some wonderful pictures of this in some of his books.


: >Ape infants, when they're born, have arms and legs that are long
: >enough to reach the mother's sides and have grasping hands and
: >feet that are strong enough to hold and bear its weight. It's a
: >design that goes a very long way back in primate evolution, maybe
: >over 100 Myr. It was probably *the* distinctive primate
: >adaptation. (Is there a primatologist in the house?) It required
: >singleton births and suggests a nomadic arboreal existence.

: The earliest primates,the plesiadapiforms,are from the
: Paleocene.That's less than 66 mya.
: (with the possible exception of Purgatorius ceratops,which is only
: know from a single tooth from the late Cretaceous)
: The plesiadapiforms did not yet have the long limbs and the hallucial
: grasping mechanism of the later primates.
: Singleton births are not required since the Callitrichidae (tamarins
: and marmosets) normally give birth to twins.

Actually, there's some question whether the plesiadapiforms or the bats
are more closely related to euprimates. The p. were short-legged and used
claws to hang on. The advanced primates (monkeys, apes, etc) were
pronograde quadrupeds until the late Miocene. It's definitely not clear
where having a single infant came into the picture. I suspect the Miocene.

: >The abandonment of this basic primate behaviour was undoubtedly
: >*the* distinctive hominid achievement. I'm sure it occurred prior
: >to bipedalism, and was a necessary condition for it.

Huh? I don't follow this argument.


: >And why should early hominids have been hairy? The parsimonious
: >and normal assumption is that all the distinctive features of a
: >species were adopted at the point of speciation. Fossil or other
: >data may modify this assumption, but we have no reason to modify
: >it in respect of hair.

: You must have mist the phenomenon of "mosaic evolution" that
: characterizes not only the hominid clade but many others.
: It may be reasonable to assume that reduced bodyhair characterizes the
: origin of Homo sapiens but it is not reasonable to shift this to
: A.afarensis without an indication.A.afarensis may well have retained
: the primitive state.
: Parsimony is not in question.The hypotheses that reduced bodyhair
: originated first in A.afarensis or in H.sapiens are equally
: parsimonious.

And completely untestable without much better material than we have. I
suspect body hair reduction occured with the emergence of H. erectus.
Note that long body hair does occur (rarely) in H. sapiens, but no
population (even those habitually naked in colder environments) is


: >> Since Australopithecines had brains not much
: >> bigger than chimps it's not likely they had the pattern of postnatal
: >> braingrowth of humans,but a pattern similar to chimps.We may therefore
: >> assume that they had precocial infants that could cling to their
: >> mothers shotly after birth.

: >This is appalling logic. I know it's standard. That makes it even
: >more appalling.

: Precociality is the primitive state in primates.Since the early
: australopithecines were apelike in many aspects of their anatomy (a.o.
: skull,brain and their adaptions to arboreality) it's likely that their
: pattern of development was apelike.
: Their is no reason to think that if they,like other apes,were able to
: carry their infants during orthograde positions in the trees,they
: suddenly had to put them down when descending to the ground and move
: bipedally.There's seems to be nothing physically or anatomically that
: makes clinging to an orthograde bipedal body more difficult than to an
: orthograde arboreal body,as long as the mother has hair and the infant
: can grasp.

: Gerrit


Harry Erwin, Internet:, Web Page:
49 year old PhD student in computational neuroscience ("how bats do it" 8)
and lecturer for CS 211 (data structures and advanced C++)