https://phys.org/news/2020-03-regular-climbing-behavior-human-ancestor.html Research identifies regular climbing behavior in a human ancestor: A new study led by the University of Kent has found evidence that human ancestors as recent as two million years ago may have regularly climbed trees. Walking on two legs has long been a defining feature to differentiate modern humans, as well as extinct species on our lineage (aka hominins), from our closest living ape relatives: chimpanzees, gorillas and orangutans. This new research, based on analysis of fossil leg bones, provides evidence that a hominin species (believed to be either Paranthropus robustus or early Homo) regularly adopted highly flexed hip joints; a posture that in other non-human apes is associated with climbing trees. These findings came from analysing and comparing the internal bone structures of two fossil leg bones from South Africa, discovered over 60 years ago and believed to have lived between 1 and 3 million years ago. For both fossils, the external shape of the bones were very similar showing a more human-like than ape-like hip joint, suggesting they were both walking on two legs. The researchers examined the internal bone structure because it remodels during life based on how individuals use their limbs. Unexpectedly, when the team analysed the inside of the spherical head of the femur, it showed that they were loading their hip joints in different ways. more at link...... the paper: https://www.pnas.org/content/early/2020/03/25/1914481117 Evidence for habitual climbing in a Pleistocene hominin in South Africa: Significance Here we present evidence of hominin locomotor behavior from the trabecular bone of the femur. We show evidence for habitual use of highly flexed hip postures, which could potentially indicate regular climbing in a South African hominin from Sterkfontein, which is either Paranthropus robustus or Homo. Second, we present evidence that Australopithecus africanus likely did not climb at the frequencies seen in extant nonhuman apes, and exhibits a modern, human-like pattern of loading at the hip joint. These results challenge the prevailing view of a single transition to bipedalism within the hominin clade by providing evidence of climbing in a more recent, non-Australopithecus South African hominin, and add to the increasing evidence for locomotor diversity in the hominin clade. Abstract Bipedalism is a defining trait of the hominin lineage, associated with a transition from a more arboreal to a more terrestrial environment. While there is debate about when modern human-like bipedalism first appeared in hominins, all known South African hominins show morphological adaptations to bipedalism, suggesting that this was their predominant mode of locomotion. Here we present evidence that hominins preserved in the Sterkfontein Caves practiced two different locomotor repertoires. The trabecular structure of a proximal femur (StW 522) attributed to Australopithecus africanus exhibits a modern human-like bipedal locomotor pattern, while that of a geologically younger specimen (StW 311) attributed to either Homo sp. or Paranthropus robustus exhibits a pattern more similar to nonhuman apes, potentially suggesting regular bouts of both climbing and terrestrial bipedalism. Our results demonstrate distinct morphological differences, linked to behavioral differences between Australopithecus and later hominins in South Africa and contribute to the increasing evidence of locomotor diversity within the hominin clade.
This outstanding video may explain a lot about the reasons why humans left the safety of the trees, and entered the much more dangerous environment of the plains. This seems very much like what "nerds" experience in today's schools. Nerds are the brainy ones, who are usually not very good at sports, but end up becoming scientists and artists. Watch this and marvel at the hidden power of mathematical function in primates in general and humans in particular and why this was causal to human evolution of cooperation and sharing of resources outside the abundant natural food supply of the forest. If this does not put to rest any question about our common lineage, the task becomes hopeless.
I was watching an episode of something about early upright hominoids, and apparently there's evidence it (bipedalism) appeared at least 6.9 mya, and possibly >11 mya. And there is now fresh debate about whether it appeared first in Africa. The accepted wisdom is that it made a walking ape more able to move between trees, and these were thinning out; an animal that could move efficiently from one patch of trees to another had an advantage. Our lineage might have climbed trees to sleep in a safe place, chimpanzees do this. Sleeping in trees might have been the only option, until we started using fire.
That would have made a quadruped of them, like all other mammalian tree - to - ground dwellers - including the baboons, the ground squirrels, and so forth. There is no advantage in slow, energy intensive, incompetent, bipedal locomotion on the ground.
I've seen a few articles by presumably informed people that say bipedal locomotion is more efficient than quadrupedal, but maybe that's for apes in general. And I feel the overall explanation for this locomotory behaviour emerging, has to include why some other apes can do it, notably the chimp and the orangutan. Orangutans are tree-dwellers, they don't spend much time on the ground usually. So they walk upright along branches in general.
Yep. One of the leading theories is that our more-efficient form of locomotion allowed us to hunt prey that was faster than us - but tired more easily.
Let's also note that the accepted wisdom is under revision as new fossil evidence emerges. To have fossil evidence of upright stance, you need leg bones is the ah, accepted wisdom. The evolutionary principle too, that species evolve due to more than one environmental pressure, implies that the savannafication of eastern Africa and the gradual disappearance of continuous forest wasn't the only reason apes walked upright, eventually. That doesn't exclude that upright-walking apes managed to colonise eastern Africa from elsewhere, where they had already evolved bipedal behaviour, for other reasons.
