From
https://paleoanthropology.org/ojs/index.php/paleo/article/view/1140/1087

Hallucal Proximal Phalanx Robusticity in
Chimpanzees, Humans, and Fossil Hominins

Humans and chimpanzees have different bipedal
foot biomechanics. One defining characteristic
of humans is the lateral-to-medial shift in
the center of pressure (COP) from midstance
into toe-off. At midstance, a larger portion
of weight is supported by the lateral forefoot,
typically under the metatarsals. At toe-off,
more of the weight is supported by the hallucal
phalanges as the hallux is the last toe to
leave the ground. In chimpanzees, COP during
stance is more variable, but tends to be
centralized under the foot, with more weight
supported by the lateral phalanges rather than
the hallux at toe-off. When human-like greater
hallucal weight-support at toe-off evolved is
unclear despite morphological studies of
chimpanzee, human, and fossil hominin hallucal
metatarsals (Mt1). Because hallucal phalanges,
and not the Mt1, comes off the ground last in
humans, investigating robusticity of the
former in chimpanzees and hominins may provide
new insight into the evolution of hallucal
toe-off biomechanics. We quantified from
μCT/CT images midshaft polar moment of area
(PMA), a proxy for bending/torsional strength,
of the hallucal proximal phalanx (HPP) in
chimpanzees (n=44) and humans (n=35). When
scaled to bone length, human HPPs are
significantly more robust (p<0.05). We then
used published AP and ML midshaft diameters
to estimate PMA, modeled as a solid beam
(sPMA), to assess relative HPP robusticity
in fossil hominins. This approach was
validated by a significant correlation
(p<0.05) between PMA and sPMA in both humans
(r2=0.72) and chimpanzees (r2=0.98); sPMA
from external diameters only overestimates
true PMA by 2–3% in both groups. Notably,
the Burtele HPP (BRT-VP-2/73g) is weak like
chimpanzees, while HPPs of Homo
neanderthalensis and H. antecessor
(ADT6-30/31) display strength comparable to
humans. HPPs of H. naledi (U.W.101-082/1452)
and H. floresiensis (LB10), however, are
weaker than humans, suggesting diverse
hallucal toe-off biomechanics among Homo
species in the Pleistocene.

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On 1.6.2024. 19:06, JTEM wrote:

 Primum Sapienti wrote:

Humans and chimpanzees have different bipedal
foot biomechanics.

Seeing how Chimps aren't bipedal, that isn't exactly
a shocker.

The LCA, what Chimps evolved from WAS bipedal. But
Chimps evolved a great deal since that time, adapting
to the forest.

That conclusion can get only somebody who doesn't know anything. Our
foot is completely different than any other foot. The midline moved, in
animals it goes over middle toe, in humans it is between big and long toe.
Further, somebody could conclude that our big toe stretched out so
that it reaches the length of other toes. The reality is actually that
other toes were cut to the length of big toe.
Furthermore, somebody may conclude that our big toe adducted to other
toes. The reality is that it were actually the other way around, other
toes adducted to the big toe.
So, from the above you can easily see that the whole foot adjusted for
the big toe:
- midline moved towards big toe
- other toes were cut to be the same length as big toe (so that they
form an arrow, with big toe and long toe at its pick)
- big toe stood at its own place, while other toes moved towards it
In primates, big toe is the most robust toe. This is the toe which you
can place on cliff bulge, and which is robust enough to hold your body
weight on it.
What other apes have has nothing to to with the changes that our foot
has. You cannot undone our modifications, once you get them, they stay.
Other apes never had those modifications, so other apes were never like
us (although other apes could have been bipedal).

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On 2.6.2024. 20:48, JTEM wrote:

 Mario Petrinovic wrote:

The LCA, what Chimps evolved from WAS bipedal. But
Chimps evolved a great deal since that time, adapting
to the forest.

         That conclusion can get only somebody who doesn't know anything.

Lol!  What a maroon...

Bipedalism is known from the fossil record to be significantly
older than any LCA. Chimps are NOT know from the fossil record
at all, not exactly. There are HALF a million year old chimp
teeth, supposedly, but teeth are far from definitive.

        ...if teeth are definitive than we had a bipedal ancestor living in Europe some 10 million years ago... something that
looked like Ardipithecus if not Australopithecus.

Skip down to the:  ***

But that's another reason why we know that paleo anthropology
is not a real science. It just kind of moves the goalpost on
a whim... or where it's bias needs it to be.

So bipedalism goes back over 6 million years, more like 7
million, at a rock bottom minimum, while our oldest Chimp
fossils are 0.5 million years old, and we can't even be
absolutely sure that it is a Chimp we're looking at!

I have postulated... Oo! That sounds so much better than
"Thought."

"I didn't think it, I POSTULATED it!"

So I have long POSTULATED that humans invented Chimps.

I fully agree with the good Doctor's model.

Not claiming that he has every little detail correct but,
nobody said he needs to. He may have the timing or the species
wrong but, Chimps arose from Australopithecus or something
along those lines.

I place the Homo/Pan split at 3.7 million years ago, the final
break, but it may have taken as much as another 2 million
years in the evolutionary crockpot to cook up something we want
to call a new Genus.

***

Long story short:  Chimps are an evolutionarily recent arrival.
They're not that old. They're not in the fossil record because
they don't exist. Least not in a form that we recognize as a
Chimp.

Our foot is completely different than any other foot.

And for how long has THAT been true?

For starters, it's NOT that different. There are differences,
of course, but there's differences within human populations
TODAY. As in "Right now."

What makes the typical human foot "so different" from any other
Ape came about... when? Not that long ago, speaking in evolutionary
terms.

         Further, somebody could conclude that our big toe stretched >> out so that it reaches the length of other toes.

This is true for many probably most people. But not all.

My big toe is just a tad shorter. I don't really know how typical
that is, but I do know it's largely irrelevant.

         Furthermore, somebody may conclude that our big toe adducted
to other toes. The reality is that it were actually the other way
around, other toes adducted to the big toe.
         So, from the above you can easily see that the whole foot >> adjusted for the big toe:

Again, WHEN do you think this all happened?

The good Doctor has pointed this out many times:

Most or the biggest changes occur long after bipedalism. So they
may not rightly be associated with bipedal locomotion but something
else instead. He posits Aquatic Ape.

He doesn't mean that Aquatic Ape only started some millions of
years after bipedalism arose. And the way that I interpret his
model is that it came down to exclusivity, or near so. Meaning,
the more the Waterside group dominated the gene pool, the more the
foot changed to that particular lifestyle.

And it makes sense, date wise. Because bipedalism is *way* older
than the Pan/Homo split, and in all but certainty as old or older
than the split with Gorillas... probably stretching back much
further.

When do I think this all happened? Well, whoever cares about such
things, he could search for it himself, I don't care.

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On 3.6.2024. 18:38, JTEM wrote:

 Mario Petrinovic wrote:

         When do I think this all happened? Well, whoever cares about
such things, he could search for it himself

WOW!  Your narcissism is off the scales!

People can "Research" your thoughts?

Just say what YOU think. That's what I asked. Narcissists seek
to shut down any conversation they can't control...

This is not a question of "control", but a question of logic. Conversation got to have sense.
What do you think they found in Trachilos? Chimp feet? "Bipedal" feet?
Human feet.

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