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

Gerrit Hanenburg (
Mon, 22 Jul 1996 11:20:32 GMT

Paul Crowley <> wrote:

>Apes at rest commonly adopt an orthograde sitting position and,
>as you suggest, their infants have no difficulty in clinging on.
>Similarly when feeding in trees an othograde position is normal;
>but then the mother's movements are slow and careful and the
>infant's safety is regularly checked; think how a modern h.s.s.
>mother would manage with an infant when climbing trees! OK, an
>early bipedal hominid might find it easier, but not much easier.

If the infant was able to cling to the mother (either ventrally or
dorsally) without additional support then both her arms could be used
in climbing,and thus it would be much easier for an early hominid to

>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.

>You should be able to see its near impossibility from my ascii drawing; to go beyond that
>I'd need an animated cartoon.

Frankly,I do not have much faith in this ascii method of judging
physical phenomena.
Just presenting such an image without any further physical explanation
(or perhaps even some experimental data) is handwaving.

>> Neither have you made it clear why it easier to hang on underneath the
>> mother with nothing to support the infant.

>I shouldn't need to. It's basic physics/engineering. You can
>hold onto a horizontal branch of a tree, wrapping your legs and
>arms around it -- even if it moves around; but you can't hold
>onto the vertical trunk of a tree unless you have good foot- and
>hand-holds; and if the vertical trunk starts moving along,
>bouncing up and down, you've got no chance of staying on.

The point is that I do not have to cling to vertical trunks during any
phase of my life,and are not thus adapted,but did you perform the
experiment with apes and monkeys?

>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.

>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.

And what do you have to back up your confidence?

>We have an excellent living model for a bipedal ape. Its brainsize
>may be bigger than we'd like, but that has little relevance to its
>locomotory behaviour. Its infant carrying behaviour is likely to
>be much closer to that of early bipedal hominids than that of a
>quadrupedal chimp.

If we have to use an extant species as a model I imagine that it's
infant carrying behavior is more like that of a vertically
climbing,brachiating or otherwise orthograde moving chimp.

>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

>> The pattern of postnatal braingrowth is
>> part of a pattern of delayed development in modern humans which causes
>> secondary altriciality.

>The cause of secondary altriciality in infant hominids is their
>inability to learn normal locomotory behaviour within a reasonable

But what causes this inability?
Why are they different from apes in this respect?

>They can't stand for the first year and competent loco-
>motion is not generally acquired until the third year. This is an
>extraordinary state of affairs which applies to no other species.
>Without normal locomotion, an infant is necessarily altricial; it
>can't fetch its food; it has to be carried everywhere (or be put
>down). No one has ever suggested that early hominid infants
>would be any different.

See Stanley,S.M.(1992),An Ecological Theory for the Origin of Homo,
Paleobiology 18(3):237-257,in which the australopithecine adaptive
complex and pattern of development is compared with that of Homo.
Also interesting is Falk, al.(1989),"Reassessment of the Taung
early hominid from a neurological perspective",Journal of Human
Evolution 18:485-482,in which they conclude that the shape of the
brain of this juvenile hominid is apelike.
Probable consequence being that Australopithecus had an apelike
pattern of (motor)development.

> If anything, they'd be worse. It's got
>nothing to do with brain size and everything to do with bipedalism.
>Imagine what it is like to have both legs amputated. You'd be
>just as "altricial" (i.e helpless).

>> 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.