Re: HP-LCA foot not chimp-like?
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Assuming Ardipithecus is close to a “common ancestor” of Homo and Pan in foot osteology is almost as unlikely as assuming such a “common ancestor” was Pan like in foot osteology. There is no evidence such a “common ancestor” existed, and considerable genetic and fossil evidence both Pan and Homo are results of mosaic, not linear, evolution. That both are complex hybrids including HGT and inter-specific gene flow events even from other distantly related Old World monkeys. And an HGT event from baboons to Pan has been detected. A plethora of symplesiomorhpies of course, that does not seem to add anything in favor of or against their arguments. Of course all extant Hominid feet share many plesiomorphorphic trasits, this hardly needs to be stated, one can easily see this just by looking at fossil and extant Hominid feet.
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From: Marc Verhaegen
Sent: Friday, March 11, 2022 3:53 PM
Subject: [AAT] HP-LCA foot not chimp-like?
The foot of the human-chimpanzee last common ancestor was not African
a response to Prang (2019)
Morgan E Chaney ... CO Lovejoy 2021 JHE
keywords: Ardipithecus, Cuboid, Midfoot
Huxley (1863) & Darwin (1871) speculated that African apes were humans’
closest living relatives,
so the notion that the HP-LCA was essentially a chimp has pervaded
inferences about its locomotor behavior.
Robust refutations of these notions are now available (Machnicki & Reno
2020, Reno 2014, Sayers cs 2012, White cs 2015),
but relying only on an examination of foot-bone lengths from
Ardipith.ramidus ARA-6/500, Prang (2019) argued that the HP-LCA foot was
likely similar to modern African apes, although it exhibits a plethora
A.ramidus lacks advanced grasping-related adaptations evident in the
feet of extant great apes, e.g.
- decreased dorso-plantar heights of their metatarso-cuneiform joint
- proximo-distal (PD) shortening of their mid-foot tarsals (Lovejoy cs
Prang (2019: 8) concluded: “modern humans evolved from an ancestor with
an African ape-like foot, ass.x terrestrial plantigrady & vertical
We contend here that data do not support this assertion over earlier
conclusions that the HP-LCA was a predom.above-branch clambering
quadruped (Lovejoy cs 2009c).
Prang’s (2019) analysis is insufficient for 3 reasons:
1) his results support only the simple conclusion that the HP-LCA
relative forefoot bone lengths were similar to extant African apes.
2) intrinsic foot proportions are at least partially reflective of body
mass. Because the body size of ARA-VP-6/500 & the HP-LCA was likely
similar to chimps, their proximity to the latter in Prang’s (2019)
phylomorpho-space plots is unsurprising & uninformative.
3) numerous primitive soft-tissue retentions in the human foot are
uniquely derived in Pan & Gorilla (Lovejoy cs 2009).
(the HP-LCA had a flat foot? --mv)