Re: An alternative to ST and AAT
Gerrit Hanenburg (G.Hanenburg@inter.nl.net)
Fri, 22 Nov 1996 13:51:58 GMT
"John Waters" <jdwaters@dircon.co.uk> wrote:
>>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?
With a shorter femoral neck the mechanical disadvantage of the
abductor muscles would be greater.
>Nevertheless, it was still less efficient than a AMH. Is that right?
Possibly.
>> 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.
Lucy's pelvic width was 132 mm and the AP diameter was 75 mm,while in
modern human females the mean values are 134 and 104 mm respectively.
Relative to the cube root of body weight the inlet width in Lucy is
4.4 and the AP diameter is 2.5. In modern human females these values
are 3.5 and 2.7 respectively. As you can see Lucy's pelvic AP diameter
was not narrow relative to body weight (Rak,Y.(1991). Lucy's pelvic
anatomy:its role in bipedal gait. J.Hum.Evol.20:283-290).
>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.
We have no reason to believe that Lucy's infants were less precocial
than chimps since there are strong indications that Austrapithecines
had an ape-like developmental pattern.
There doesn't seem to be an obstetric reason for Lucy's relatively
wide pelvic inlet since she didn't have to deliver large brained
babies.
>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?
Another feature of Lucy's pelvis that attracts attention is that about
two thirds of the iliac blade is directed posteriorly (in modern
humans this is approximately half). This might indicate that the
gluteal musculature played a greater role in extension of the thigh,a
function that would have been important in vertical climbing.
Gerrit
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