Re: AAH update (was: Bipe
Pat Dooley (patdooley@aol.com)
9 Jul 1995 19:45:55 -0400
Response to Alex Duncan
>
>In article <3t7ar6$7jq@newsbf02.news.aol.com> Pat Dooley,
>patdooley@aol.com writes:
>
>> According to the DNA evidence, Chimps and Bonobos are
>> our closest relatives, and we are more closely related to them
>> than they are to Gorillas. You would never believe that was
>> the case based on comparative anatomy.
>
>Have you ever taken an anatomy course?
No.
>The most astonishing thing about the anatomy of chimps,
>gorillas, and humans is how similar they are to
>one another. I can think of far more aspects of African hominoid anatomy
>in which we are nearly identical to chimps and gorillas than aspects that
>are different.
Well, you'd expect them to be pretty similar, given the degree of
relationship. In fact you'd expect them to be as similar as, say,
horses and the various zebra species. But simple observation tells
you there are major differences.
(i) Hairlessness
(ii) Bipedalism and the host of skeletal differences that come with
100% bipedalism.
(iii) The relative position of the larynx
(iv) Subcutaneous fat layer (Have you ever done a comparative
dissection of the various species under discussion)
(v) Downward pointing nostrils
(vi) Cooling mechanisms
(vii) Loss of oestrus in human females
(viii) Different structures for supplying blood to the brain
(ix) Radically different degree of adaptability to aquatic environments
I'd be more impressed with your statement of how similar we are
to apes if you could give some other examples of closely related
species that have more radical differences than there are between
humans and apes.
>As far as humans being more closely related to chimps
>than to gorillas -- 1) this notion is controversial, and not as well
>supported as you seem to think, and 2) there are a number of
>synapomorphies (e.g. early fusion of premaxillary suture) that we share
>with chimps and not with gorillas.
2) contradicts 1), Does it not?
>Are you familiar with the distinction between apomorphies and
plesiomorphies?
No.
I have not had the advantage of an anatomy course
>
>> What is even more surprising is the short time frame in which those
differences
>> emerged. Most of the skeletal transformation occurred in the
>> interval between the initial separation from the ape-line, say
>> 7.5 mya, and the appearance of fully bipedal Australopithecus,
>> say 4 mya.
>
>What exactly do you mean by saying Australopithecus was fully bipedal?
>Yes, they were bipeds, WHEN THEY WERE ON THE GROUND (and not in the
>trees). However, their bipedalism seems to have differed in some pretty
>substantial ways from that of modern humans. Most of the differences
>seem to be related to a "compromise anatomy" that enabled terrestrial
>bipedalism coupled with tree climbing capacities.
I just reread the section in Lucy's Child pages 194ff discussing this very
issue. Seems to be a point of contention as to the degree of bipedalism
versus arborealism displayed by Afarensis.
>> That is extremely rapid evolution, and could only
>> have come about due to a major environmental change; a change
>> that somehow seems to have bypassed just about every other
>> mammal group in Africa over the same time scale.
>
>How can you say how rapid it is until you've quantified it? To my eyes
>the most astonishing thing about the australopithecine skeleton is the
>similarity to those of the African apes. Contrary to what you've placed
>in other posts, the reorganization of the ape hind limb skeleton to
>arrive at an australopithecine hindlimb skeleton is not "major". Fairly
>minor changes involving the cranio-caudal length of the pelvis, the
>bicondylar angle of the knee, and some details of the foot seem to be the
>only real changes that occured. Relatively minor shifts in muscle
>placement and size probably accompanied these shifts in skeletal anatomy.
> Also, contrary to what you might think, Leakey & Lewin (and Johanson)
>are not authorities on functional anatomy. I suggest you read papers by
>Stern & Susman and their colleagues.
Page 200 of Lucy's Child shows Owen Lovejoy's reconstruction of Lucy's
pelvis compared to a human pelvis and a chimpanzee. What you desribe
as minor looks pretty major to my untrained eye. The chimpanzee pelvis
stands out as startlingly different.
Is there a little tension between L,L,L & J and S & S? It's pretty obvious
which side you are on.
> Finally, this change did not bypass every other mammal group in
>Africa. Bovids are arguably among the most successful creatures in
>Africa today, and they began their major radiation about the same time we
>see evidence for hominid divergence from apes.
>
>Alex Duncan
So, name three bovid species as closely related as humans, chimps and
gorillas, in genetic terms, yet just as different physically.
Pat Dooley
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