Re: An alternative to ST and AAT
Thomas Clarke (clarke@acme.ucf.edu)
9 Nov 1996 15:43:39 GMT
In article <3283F0DE.1421@scn.org> Phillip Bigelow <bh162@scn.org> writes:
>> Thomas Clarke wrote:
>> > There are lots of saltative bipeds in Australia.
>Are they saltative in EXACTLY the same way?
Of course not. But a kangaroo rat is more alike in saltation to a kangaroo,
than either is to a human's bipedal locomotion.
>> > There were lots of bipedal (tripedal?) dinosaurs.
>Were they bipedal in EXACTLY the same way?
Again. Tyrannosaurus moved more like a velociraptor, than either resembled
a hominid in locomotion.
>> > But only one who walks like a man.
>This is not true. Brachiating arboreal primates "walk like a
>man" when they find themselves (infrequently) on the ground.
>The only difference is that, morphologically, they don't
>locomote EXACTLY in a human style gait. But that is to be
>expected. After all, Tom, they ARE different species.
Do they have locking knees?
This type of discussion is, of course, a matter of degree.
Can a brachiating arboreal primate walk twenty miles?
I just perceive a larger difference than you do, I guess.
Actually, as I think about this, I will concentrate on the
knee. I think the human (australopithicene?) knee is unique.
>> > Does this not suggest the possibility of special evolutionary
>> > circumstances? If the circumstances were not special then why
>> > are there not lots of animals that walk like a man?
>Why are there not lots of birds that walk (and run) JUST like an
>ostrich? Why are there not lots of birds that walk JUST like
>a stork? Why are there not lots of birds that walk JUST like
>a grouse?
OK. Now my question can be more precise. Do ostrich's and storks
have unique anatomical features related to their style of walking?
> The answer (at the risk of sounding like I am teaching a pre-
>schooler)
Since it does some like a pre-school teacher, I will cut it off.
....
>Example: Rheas and ostriches both shared a common adaptive
>circumstance that led to their loss of flight (geographic
>isolation; abundant ground food; loss of major predation).
>Yet, these runner-specialized birds have a different pedal
>count (three for the rhea; two for the ostrich), and a different
>stride pattern and different stride length.
I would argue that number of toes and stride length/pattern
are not essential differences. They could easily result from
genetic drift and other random factors.
>Similar environmental pressures for each of them; yet two different
>morphological outcomes.
As I said, I don't see the significance of the morphological
differences. Perhaps this is specism, perhaps not.
Human hands and other primate hands are pretty similar. I don't
feel any great need for a special explanation of how the human
hand developed. Even the human face is pretty much a modified
ape face - the variability among canine faces shows how plastic
this is. Even the human brain can be seen as just an enlarged
primate brain.
Howeever, the human foot and human knee are a lot
different from the corresponging primate features.
>Tom, it amazes me that you still insist on some type of "special"
>origin for hominids. It also amazes me that, in spite of us having
>a similar conversation on this topic last year, you still make the
>same statements today.
You did not convince me. I just tired of discussion on the net for a while.
Hominids are unique. The fact that we are conversing in this
way on this medium proves it.
If the circumstances leading to the unique species of which I am
a member were not unique, then why did it not happen before?
I suppose it could be just dumb luck that primates became
bipedal/intelligent first (or should I write it the other way?)
and since human history seems to show that the existence of
one intelligent species precludes the existence of others,
primates are it.
But .... this is a science group and just saying "dumb luck"
is not very satisfactory. One would like to know why and how.
What made primates the lucky ones and not some bird or reptile?
Why not bears?
Tom Clarke
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