You heard that headline here first,
but the authors’ citations indicate the thought has been percolating for decades. However, without a trait-based phylogenetic analysis, like the LRT (subset Fig 2), an alternate hypothesis of human origins remained nebulous coffee talk. If you want to play on this field you have to provide a better set of human ancestors than australopithecines (Fig 1). No cladogram has done that yet – other than the LRT.
Vanneechoutte et al 2023 wrote,
“In summary, hypotheses that attempt to explain how a semi-erect Homo/Pan last common ancestor transitioned into the bipedal australopithecines as an adaptation to life on the savannah appear to be ill-conceived and moreover seem to have been superfluous from the very start. We review the numerous similarities between australopithecines and extant African apes, suggesting that they are possibly not hominins and therefore not our direct ancestors. We suggest that we may have been barking up the wrong ancestral tree, for almost a century.”
“It appears that there was never a transition from a semi-erect (diagonograde) Homo/Pan ancestor to orthograde hominins, but instead there were separate transitions from an already orthograde hominine ancestor to the extant semi-erect chimpanzees and gorillas.”
That last common ancestor: (genus: Hylobates, Fig 1), is bipedal whenever terrestrial. That’s the ‘first step.’
“the savannah hypothesis was a narrative conceived to explain a transition that never happened.”
Or maybe it did somewhere else with a different clade of apes.
Figure 2. The gibbon lineage leading to humans. At right is Australopithecus, a bipedal ape by convergence with humans.
The authors explored
historical roots and offered critical considerations, but did not provide a phylogenetic analysis, like the LRT (subset Fig 2 from 2022).
Figure 2. Subset of the LRT focusing on primates after the addition of Australopithecus and Pongo.
The authors cited several earlier reports when they wrote,
“Keith [1923] recognized “the antiquity of orthograde posture”, pointing to hylobatids and to late-Oligocene/early-Miocene dryopithecines. Morton [1926] had also realized that the bipedalism of early hominoids is not in disagreement with the orthograde posture of extant hylobatids: “The gibbon’s primitive position in the anthropoid group has added value in that it strongly suggests the linking of our modern bipedalism with an early stage of erect arboreal habits in the ancestral anthropomorphous stem.” and that: “Tree life is the only form of environment, and brachiation the only locomotive habit whereby the structures about the hipjoints would be given the opportunity to become gradually modified for an erect posture.” A study of the frequency of bipedalism in almost 500 zoo-housed hominoids and cercopithecines found that all could move bipedally, with hylobatids engaging most frequently in bipedal locomotion”.
All these studies lacked was a trait-based
phylogenetic analysis (Fig 2).
In their conclusion Vaneechouette et al wrote,
“Furthermore, since orthogrady and, at the very least, facultative/postural bipedalism were already present in the Homo/Pan ancestor, it follows that our bipedalism can no longer be regarded as the initial and necessary condition that made possible our other numerous anomalous characters, including large brain size, also because brain size did not increase significantly during the millions of years that the bipedal—probably nonhominin—australopithecines and their predecessors existed.
Finally, considering australopithecines as possible ancestors of extant African apes, might help to resolve several enigmas, such as the counterintuitive lack of fossils of the once numerous African apes and the unexpected absence of PtERV-elements in our genome.”
The LRT (Fig 2) nested Australopithecus basal to Pan + Gorilla in 2022.
The LRT is a hypothesis of interrelationships still needing an independent study with a similar taxon list to confirm, refute or modify it.
References
Keith A 1923. Hunterian Lectures on Man’s posture: Its evolution and disorders: Given at the Royal College of Surgeons of England. British Medical Journal 1:451–454.
Morton DJ 1926. Evolution of man’s erect posture (preliminary report). Journal of Morphology 43: 147–179.
Vaneechouette M, Mansfield A, Munro S and Verhaegen M 2023. Have we been barking up the wrong ancestral tree? Australopithecines are probably not our ancestors. Nature Anthropology DOI: 10.35534/natanthropol.2023.10007
The Pterosaur Heresies 