Re: An alternative to ST and AAT
John Waters (jdwaters@dircon.co.uk)
22 Nov 1996 08:37:07 GMT
Gerrit Hanenburg <G.Hanenburg@inter.nl.net> wrote in
article <56np55$2jp@news.NL.net>...
> "John Waters" <jdwaters@dircon.co.uk> wrote:
>
> >## With a long femur neck the angle of the femur from
the
> >hip to the knee is greater. Modern humans have less of
an
> >angle. The lateral support system is a series of
muscles,
> >the gluteus medium and minimum, that run from the crest
of
> >the iliac blade to the greater trochanter of the femur.
As
> >we lift one foot off the ground, the lateral support
system
> >fires and pulls our trunks toward the supported side so
we
> >don't fall over.##
>
> Lucy had a relatively wide pelvic inlet,and as result of
this also a
> relatively long bi-acetabular width (distance between the
hip-joints).
> Because the hip joint acts as the fulcrum of the lateral
balancing
> system she has a long body-weight lever arm resulting in
a greater
> pelvic tilt during the stance fase of walking. The
abductor muscles
> (gluteus medius and minimus) have to work harder to
counteract this.
> To compensate for the mechanical disadvantage of the
abductors Lucy
> has a wide laterally flaring iliac blade and a long
femoral neck.
> So,contrary to the above,a longer femoral neck would make
the lateral
> balancing system in Lucy more efficient.
JW: You mean more efficient than it would have been with a
short femoral neck? Nevertheless, it was still less
efficient than a AMH. Is that right?
> But why did she have such a wide pelvic inlet?
JW: Yes, relatively speaking wider than a AMH. But to
compensate the pelvic canal was much narrower from front to
rear. I don't know whether there would be any structural
advantages with such an arrangement, but if it led to
increased africial developments as some authorities
believe, this would seem a high price to pay. Mind you, the
increased alfricial development would have been very
slight, so I don't suppose there would have been much of a
relative disadvantage.
In addition, the leg bones are described as being very
dense, implying strong leg muscles. I imagine this is
similar to Chimpanzees, although I don't know. If it is,
then it might imply that a considerable amount of vertical
climbing was still part of the behaviour. In this regard, a
wide pelvis might give more leverage. Is this a
possibility?
John
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