Re: An alternative to ST and AAT

Gerrit Hanenburg (
Tue, 03 Dec 1996 17:23:11 GMT (Paul Crowley) wrote:

>Are there any discussions in the literature of the biomechanics
>involved in the alteration of the mother/infant dyad from a
>quadrupedal to a bipedal gait? They should focus on late
>infancy (about 3-4 years of age) when the weight of the infant
>would be a strongly inhibiting factor on the ability of the
>mother to adopt a bipedal stance.

There are indications that Australopithecines had a developmental
pattern similar to that of chimpanzees (Smith 1991).
Since chimpanzees achieve complete locomotor indepence at the age of
3.5-4.5 years (Goodall 1968) the biomechanics of infant carrying at
that age seems irrelevant. Australopithecine infants of a similar age
(e.g.Taung) may be expected to have achieved locomotor independence.
The biomechanical differences between quadrupedal and bipedal carrying
in early hominids depend on how exactly the infant held on to its
mother. Forces acting on the arms of the infant are likely to have
been tensile as in quadrupedal carrying but may have been either
tensile or compressive in the hindlimbs depending on whether the
foothold was above or below the level of the infant's hips. If we
assume a bodyweight similar to chimpanzee infants the forces in the
limbs would have been more less the same but would have been less if
the infant was supported by the mother.

Goodall,J.(1968), The behaviour of free-living chimpanzees in the
Gombe Stream Reserve. Animal Behaviour Monographs 1:161-311.

Smith,B.H.(1991), Dental development and the evolution of life history
in Hominidae. Am.J.Phys.Anth.86:157-174.