Evolution of the Human Foot

Nature News has an interesting examination of how the human foot evolved the arch, the singular most important aspect in the ability to perform bipedal locomotion.  Glen Lichtwark and Luke Kelly write:

Humans evolved to walk and run effectively on the ground using two feet. Our arched foot, which is not a characteristic of other primates, is a unique feature crucial for human bipedalism. The arch provides the foot with the stiffness necessary to act as a lever that transmits the forces generated by leg muscles as they push against the ground. The arch also retains sufficient flexibility to function like a spring to store and then release mechanical energy. Writing in Nature, Venkadesan et al.1 present a new view of how foot stiffness is regulated. Their finding not only has exciting implications for understanding foot evolution, but also provides a possible framework when considering foot health and how to design better footwear.

The authors note that there are two different arches present in the human foot, the longitudinal arch, which is more familiar to people and the transverse arch. They argue that the transverse arch (across the top of the foot) is as important for walking as the longitudinal arch. The authors note that the transverse arch has been neglected in sports and medicine and that more research needs to be done in this area. 

Upright Ape?

Multiple outlets are reporting on the discovery of a fossil ape that appears to have at least a partially facultatively bipedal stance.  Here is the Fox News version of events:

The remains of an 11 million-year-old ape suggest that our ancestors started to stand upright millions of years earlier, according to scientists.

A team of researchers claims the fossilized partial skeleton of a male ape that lived in the humid forests of what is now southern Germany bears a striking resemblance to modern human bones. In a paper published on Wednesday by the journal Nature, they concluded that the new species — dubbed Danuvius guggenmosi — could walk on two legs but also climb like an ape.

The findings “raise fundamental questions about our previous understanding of the evolution of the great apes and humans,” Madelaine Boehme of the University of Tuebingen, Germany, who led the research, told The Associated Press.

Here is how the Nature paper actually reads:

Here we describe the fossil ape Danuvius guggenmosi (from the Allgäu region of Bavaria) for which complete limb bones are preserved, which provides evidence of a newly identified form of positional behaviour—extended limb clambering. The 11.62-millionyear-old Danuvius is a great ape that is dentally most similar to Dryopithecus and other European late Miocene apes. With a broad thorax, long lumbar spine and extended hips and knees, as in bipeds, and elongated and fully extended forelimbs, as in all apes (hominoids), Danuvius combines the adaptations of bipeds and suspensory apes, and provides a model for the common ancestor of great apes and humans.

First, this is way-the-heck back there, some five and a half million years before the first actual evidence of bipedalism (Orrorin). Second, there are no “hip” remains. The only post-cranial remains are long bones.  Much is inferred.  In hominins, the femoral neck and the connection to the femoral head provide much diagnostic locomotion information.  The fossil remains for this region are very scant, consisting only of a partial head.  Much of the argument for even some bipedality rests with the tibial angle, to wit:

The near perpendicular tibial angle is a shared character between hominins and Danuvius and supports the inference of a habitual valgus knee position and bipedalism for the new genus.

I think a new genus designation is certainly warranted. I have grave reservations about the “bipedalism” designation. We have possible evidence from Crete at 5.5 million years for bipedalism in the form of footprints. That is as far north as it gets.  All of the other evidence we have for the emergence of hominins and bipedalism comes from North Africa.  It is far more likely that this represents an independent adaptation/homoplasy for this hominoid.   If we had more evidence from later in the Miocene or, better yet, the Pliocene, then this might carry more weight.

More Evidence For Bipedality at 4.5 MYA

Out of Case Western Reserve comes a study of some new fossil material that sheds like on early human bipedal adaptation.  From ScienceDaily:

Scott W. Simpson, PhD, led an analysis of a 4.5 million-year-old fragmentary female skeleton of the human ancestor Ardipithecus ramidus that was discovered in the Gona Project study area in the Afar Regional State of Ethiopia.

The newly analyzed fossils document a greater, but far from perfect, adaptation to bipedalism in the Ar. ramidus ankle and hallux (big toe) than previously recognized. "Our research shows that while Ardipithecus was a lousy biped, she was somewhat better than we thought before," said Simpson.

While the weight of evidence has always a bit more than slightly favored the facultative bipedality of Ardipithecus ramidus, this research provides greater support for this hypothesis.  In my class, I stress the difference between facultative bipedality (practiced by Ardipithecus) and obligate bipedality (practiced by every other hominin).  Additionally, from the article¹:

The more complete adoption of bipedality in the australopiths resulted in the loss of functionally critical adaptations to arboreality present in Ardipithecus such as a grasping, opposable hallux, an antero-posteriorly broad pelvis with reorganization of the origin (and most likely function) of the hamstring muscles, and a more derived humero-femoral ratio. The changes in the size and structure of the dentition in the subsequent australopiths (larger molar and premolar crowns, increased enamel thickness, more robust mandibles) indicates a major behavioral and dietary shift for most hominins (perhaps excluding the species indicated by the Burtele foot) that occurred about 4.2 Ma with the earliest appearance of Australopithecus (Leakey et al., 1995, White et al., 2006).

Many of these changes, then, appear to have occurred somewhat rapidly, once the early hominins moved away from the forest and into the fringe.  Once we thought that bipedality originated in the forest/fringe.  The Ardipithecus data have killed this hypothesis. 


¹Scott W. Simpson, Naomi E. Levin, Jay Quade, Michael J. Rogers, Sileshi Semaw. Ardipithecus ramidus postcrania from the Gona Project area, Afar Regional State, Ethiopia. Journal of Human Evolution, 2019; 129: 1 DOI: 10.1016/j.jhevol.2018.12.005

New Laetoli Footprints Demonstrate Full Bipedality

A story running in Newsweek and the Washington Post (and other outlets, presumably), details research into the newly discovered fossil footprints at Laetoli dated to 3.6 mya that clearly show a modern human gait.

Two sites in Laetoli, Tanzania, feature footprints of human ancestors who lived about 3.6 million years ago. They were members of the genus Australopithecus. That's the genus of “Lucy,” the 3.2 million-year-old human ancestor whose fossilized bones were discovered in Ethiopia in 1974.

David Raichlen, an evolutionary anthropologist at the University of Arizona, has studied the Laetoli footprints and compared them to footprints made by human volunteers in laboratory settings. He examined footprints of individuals walking normally and also those walking with bent knees and bent hips. (Scientists who study locomotion use the acronym BKBH). The Laetoli footprints more closely match modern human footprints.

“Upright, humanlike bipedal walking goes back 4 to 5 million years,” Raichlen told The Washington Post in advance of a symposium on the evolution of human locomotion, which took place Sunday at the Experimental Biology 2018 conference in San Diego.

This dovetails with the recent findings that Ardipithecus, a hominin dated to around 4.4 mya, likely could travel equally well on the ground or in the trees.  Oddly, the WaPo article doesn't mention this.  

3.3 Million Year Old Vertebral Column Confirms Human Pattern of Au. afarensis

The science site PhysOrg has posted a story on a study of the 3.3 million year old fossil from the site of Dikika, in the Afar Triangle.  The fossil, known as Selam, is an almost complete skeleton of a 2 ½ year-old child. From the story:

Many features of the human spinal column and rib cage are shared among primates. But the human spine also reflects our distinctive mode of walking upright on two feet. For instance, humans have fewer rib-bearing vertebrae - bones of the back - than those of our closest primate relatives. Humans also have more vertebrae in the lower back, which allows us to walk effectively. When and how this pattern evolved has been unknown until now because complete sets of vertebrae are rarely preserved in the fossil record.

"For many years we have known of fragmentary remains of early fossil species that suggest that the shift from rib-bearing, or thoracic, vertebrae to lumbar, or lower back, vertebrae was positioned higher in the spinal column than in living humans. But we have not been able to determine how many vertebrae our early ancestors had," said Carol Ward, a Curator's Distinguished Professor of Pathology and Anatomical Sciences in the University of Missouri School of Medicine, and lead author on the study. "Selam has provided us the first glimpse into how our early ancestors' spines were organized."

This gives us much better evidence of how bipedality was practiced in some of the earliest hominins. We know, from the footprints at Laetoli and the hip remains of Lucy, that Au. afarensis was bipedal but now we know that the rib structure had evolved into a more human pattern. 

Science Daily: "Anthropologists Confirm Link Between Cranial Anatomy and Two-Legged Walking"

This sort of fits under the category of "gee, who knew" but it is nice to finally have confirmation of something that has been tacitly understood for almost ninety years.  Science Daily writes:

The study, published in a forthcoming issue of the Journal of Human Evolution, confirms a controversial finding made by anatomist Raymond Dart, who discovered the first known two-legged walking (bipedal) human ancestor, Australopithecus africanus. Since Dart's discovery in 1925, physical anthropologists have continued to debate whether this feature of the cranial base can serve as a direct link to bipedal fossil species.

Okay, first, the controversial nature of this is being massively overstated. There is very little doubt, based on comparative anatomical studies, that the placement of the foramen magnum is directly indicative of the kind of locomotor pattern that a given animal employs. That is what clued Dart in to the whole idea that the Taung child represented a biped in the first place. Its foramen magnum was not in the place that you would have expected it to be if the individual had been either a quadrupedal baboon or extinct ape (of which there were none in South Africa). It was, however, located in the same place as in bipedal humans. Further studies demonstrated that if you placed the Taung skull on a quadrupedal animal, it didn't work. The animal would have its face pointed down all of the time, instead of out, like your average quadruped. Put simply, the Taung child was an early biped and there was no reason to think anything differently.

Once again, comparative anatomical studies to the rescue!

As part of the study, the researchers measured the position of the foramen magnum in 71 species from three mammalian groups: marsupials, rodents and primates. By comparing foramen magnum position broadly across mammals, the researchers were able to rule out other potential explanations for a forward-shifted foramen magnum, such as differences in brain size.

According to the findings, a foramen magnum positioned toward the base of the skull is found not only in humans, but in other habitually bipedal mammals as well. Kangaroos, kangaroo rats and jerboas all have a more forward-shifted foramen magnum compared with their quadrupedal (four-legged walking) close relatives.

Well, now we know for sure...sort of.   

Did Competition Put Us On Our Feet?

Simply, yes. That is not earth-shattering. Cambridge News has a story on work done with chimpanzees that seems to confirm that behavioral alterations in higher level primates help with competitiveness. They write:

Anthropologists studying chimpanzees found the great apes, who usually walk on all fours, walk upright and free their hands for carrying when they need to grab more hard-to-find resources in one go, in the face of competition.

The team from the University of Cambridge and Kyoto University in Japan believe the benefit of “first come, first served” and getting a bigger share of scarce food supplies could, over a long period of time, have led some of our earliest “hominin” ancestors to evolve into “bipedal” primates walking on two legs permanently instead of four.

This has always been part of the bipedality model, that early hominins exploited the forest/fringe environment where they could get what they needed from the trees and from the savannas. The fact that Ardipithecus ramidus demonstrated bipedality in a forested environment sort of threw cold water on the more conservative of those models but it is also clear that even the level of bipedality continued to evolve over time and that, by the time later australopithecines had completely human, obligate bipedal locomotion, these hominins were living in the open and competing for those resources. It was at this point that our brains began to expand as well.

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The Role of Savannahs in Human Evolution

It now appears that grassland savannahs stretched further than originally thought during the critical time when human precursors became bipedal. As the Gence France Presse reports:

"There have been open habitats for all of the last six million years in the environments in eastern Africa where some of the most significant early human fossils were found," said Thure Cerling, a professor at the University of Utah and lead researcher of the study.

"Wherever we find human ancestors, we find evidence for open habitats similar to savannahs - much more open and savannah-like than forested," he said in a statement.

It still remains to be explained how Ardipithecus developed a bipedal gait within a forest environment, though.

BioLogos Post

The third BioLogos post, on the origins of bipedality and Ardipithecus, is up. Darrel actually changed the title a bit from “Bipedality—the Hallmark of Humanity” to just “Bipedality” to prevent a potential critical backlash. That is understandable.

As Darrel correctly pointed out, the hallmark of humanity is entrance into the Kingdom of God. It is important when reading the post that you keep this in your mind. That it looks like God took His time with us does not change that in any way. We are creations of God and His chosen creation. Let me know what you think.

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Ardipithecus Meets Modern Technology

The question of whether or how well Ardipithecus could walk has been hot since the discovery and description of the find were announced last year. Now a company that specializes in three-dimensional biomechanical reconstructions has taken an interest. According to the story in Send2Press:

LifeModeler, Inc. has reason to pay close attention. The company's LifeMOD™ biomechanical simulation software helped researchers understand how the 4.4 million-year-old Ardipithecus ramidus female walked and moved.

LifeModeler's founder, Shawn McGuan, worked with anthropologist C. Owen Lovejoy of Kent State University to create 3D models of the bones and muscles of this specimen first discovered in 1992.

Not only were they seeking information as to how her bones and muscles fit together, they also wanted to visualize the range of motion she was capable of, based on her anatomy. A detailed model of Ardi's foot provided particular insight for Lovejoy and the extensive team working on the project which was first disclosed last week in the journal Science.

The LifeMOD software determined that Ardi was the first fossil hominid to have had an opposable big toe, meaning she was able to live in the tree canopy and walk nearly upright on the ground. Research shows that a small bone inside a tendon maintained rigidity in her big toe.

Not exactly a nail in the coffin, but this will go a long way to establishing Ardipithecus as a real hominid. Much of the debate focused on the reconstruction of the pelvis and the foot anatomy was, for the most part, uncontroversial. More to come, I am sure.


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New 3.6 Million Year Old A. afarensis Remains

Science Daily reports that Yohannes Haile-Selassie's team in Ethiopia have found the remains of a 3.6 million year old Australopithecus afarensis individual that preserves enough of the post-cranium (below the head) to determine that bipedalism had completely taken hold of this species by this time. Of the individual, which is taller than Lucy (AL-288), he says this:

"As a result of this discovery, we can now confidently say that Lucy and her relatives were almost as proficient as we are walking on two legs, and that the elongation of our legs came earlier in our evolution than previously thought," he said in a statement. He explained, "

"All of our understanding of Australopithecus afarenis' locomotion was dependent on 'Lucy.' Because she was an exceptionally small female with absolutely short legs, this gave some researchers the impression that she was not fully adapted to upright walking. This new skeleton falsifies that impression because if 'Lucy's' frame had been as large as this specimen, her legs would also have been proportionally longer."

There is, thus, considerable variability in A. afarensis (this may yet revive the multiple species hypothesis that was put forth in the late 1970s about this material) This finding is expected, however, if the tracks at Laetoli are those of A. afarensis. We have good evidence that those are the tracks of a completely bipedal hominid.

If Ardipithecus ramidus ('Ardi') represents an ancestor to Australopithecus afarensis, then a considerable amount of evolution in bipedality occurred within 800 k years. A check of PNAS reveals that the paper is not out yet, but should be in a few days. Within the context of the debate concerning Ardipithecus' place on the fossil bush and the status of the reconstruction, it is important to remember what Owen Lovejoy wrote concerning Ardipithecus:

Ardipithecus ramidus now reveals that the early hominid evolutionary trajectory differed profoundly from those of our ape relatives from our clade’s very beginning. Ar. ramidus was already well-adapted to bipedality, even though it retained arboreal capabilities. Its postcranial anatomy reveals that locomotion in the chimpanzee/human last common ancestor (hereafter the CLCA) must have retained generalized above-branch quadrupedality, never relying sufficiently on suspension, vertical climbing, or knuckle walking to have elicited any musculoskeletal adaptations to these behaviors.

It is clear that, by 3.6 million years ago, those arboreal tendencies were gone. While it is still being debated whether or not Ardipithecus developed bipedality in the forest or in the forest fringe, the dessication of the landscape continued during the late Pliocene, and the remains of Kadanuumuu strongly suggest that early A. afarensis had completely adapted to this landscape.

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Not Out of the Trees?

The Independent has a story about research indicating that our earliest human precursors might not have been as arboreal as originally thought. Michael McCarthy writes:

Humanity's immediate predecessors may have had trouble climbing trees, research suggests – so they may not have been as ape
-like as many experts believe.

Scientists have arrived at this conclusion after making a close study of the way chimpanzees scale trees – virtually vertically and with ease – and then comparing chimpanzee ankle joints with those of hominins, humans' ancestors.

The hominins lived between 1.5 and 4.1 million years ago, a relatively short time after proto-humans and chimpanzees split from a common ancestor (generally thought to have been between four and eight million years ago). Many experts have argued that this ancestor was probably quite chimpanzee-like, and as a result it has been widely assumed that the earliest humans were ape-like, too.

Given what we know about the bipedalism of Ardipithecus and Australopithecus afarensis, this doesn't seem to me to be too much of a surprise. It is quite possible that bipedality evolved due to selective pressures for a more terrestrial lifestyle, perhaps because they were being out competed by the precursors of modern chimpanzees.

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Bipedalism and Tool Use: Connected?

It has been generally thought that the evolution of bipedality, which we now suspect took place in a forested environment sometime between 4.5 and 5.0 megayears ago, spurred on the invention of and use of stone tools such as the Oldowan and Developed Oldowan. Now it is being suggested that this link is greater than originally thought:

"This goes back to Darwin''s The Descent of Man," said Campbell Rolian, a scientist from the University of Calgary in Canada who led the study.

"Charles Darwin was among the first to consider the relationship between stone tool technology and bipedalism," he said.

"His idea was that they were separate events and they happened sequentially - that bipedalism freed the hand to evolve for other purposes," he added.

"What we showed was that the changes in the hand and foot are similar developments and changes in one would have side-effects manifesting in the other," he explained.

The connexion gets stronger.

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Casey Luskin and Ardipithecus

Much to my chagrin, I missed this a few weeks back, when Casey Luskin put up an article on the new Ardipithecus remains. Hyperbollically titled Artificially Reconstructed “Ardi” Overturns Prevailing Evolutionary Hypotheses of Human Evolution, Luskin writes:

The missing link presently being touted in the media, Ardipithecus ramidus, has had more reconstructive surgery than Michael Jackson. Assuming that their "extensive digital reconstruction" of its "badly crushed and distorted bones" is accurate, what does A. ramidus (or “Ardi” as the fawning media is affectionately calling it) really show us that we didn’t already know? We already knew of upright walking / tree-climbing, small-brained hominids—that’s what Lucy, an australopithecine, was. We already knew that there were australopithecine fossils dating back to before 4 million years, and this fossil is only a little bit older. So what does this fossil teach us? Assuming all the reconstructions of Ardi's crushed bones are objective and accurate, this fossil teaches us at least one very important thing: prevailing evolutionary explanations about how upright walking supposedly evolved in humans, confidently taught in countless college-level anthropology classes, were basically wrong.

The Ardipithecus remains were painstakingly reconstructed over a period of ten years, during which clues about her morphology were extracted. Mr. Luskin is not correct in his assertion that we already knew about australopithecine fossils before 4 gigayears ago. The earliest clear evidence that we had for bipedality dated to around 3.6 mya. It is clear that bipedality was established by that time but we didn't have anything before that. The description of the Ardipithecus remains tells us that bipedality was incipient 4.4 mya.

He is also wrong about what was being taught. It has never been clear how bipedality arose and there have been competing models to explain its development that have been nothing more than hypothetical because we didn't have anything to test them on. The most popular model was the "forest/fringe" model in which bipedality arose as the climate cooled and the savannas expanded. The precursors of the Gorillas and Chimpanzees adapted to the forest proper, while the baboons and their ilk took to the grasslands. That left the area in between where a hominid could develop that could take advantage of both. Guess what? That model turned out to be wrong. So what? Now we know that bipedality arose in a forested environment and our models can proceed from that knowledge. That is how science works. It learns from its mistakes.

Luskin is also wrong about what else it tells us. It tells us that this early biped was also completely adapted to the trees, and was, thus, in a position to take advantage of the shrinking forests when the dessication began around 4 mya. We still don't know exactly how bipedality developed, but we know that it did.

Luskin also writes:

It’s rarely discussed, but there are a number of upright-walking, forest-dwelling ape-like species known from prior to 10 million years ago that are thought to be far removed from human ancestors. This implies that bipedalism in a hominoid does not necessarily qualify an individual as a human ancestor, and it also casts doubt on classical explanations for the evolution of bipedalism.

WHAT???? Which ape-like species is he talking about? There are absolutely no bipedal apes of any kind in the Miocene prior to seven million years ago. If there had been, this would have been huge news! He, of course, cites no information here. It isn't rarely discussed. Its not discussed at all!! I have written Mr. Luskin and asked him which remains he is referring to. I know it ain't Dryopithecus, Sivapithecus, Oreopithecus, Kenyapithecus or Gigantopithecus.

Luskin, correctly, does point out that there is some skepticism in the palaeoanthropological community about whether the case for bipedality holds up, notably from Bill Jungers at Stony Brook and Bernard Wood, at GW, in Washington, D.C., although Wood states that the head has better evidence for bipedality. This is, perhaps, true and we do need to be cautious about hanging our hats on one specimen, but the evidence, as presented by White, Asfaw and Lovejoy, is compelling. Luskin concludes thus:

So what do we have with “Ardi”? We have an extremely crushed “Irish stew” fossil that has undergone extensive reconstruction in order to become part of a PR campaign to make bold claims of ancestral status to the human line, even though at base its qualities are very similar to previously known fossils, and there's a lot of skepticism about the claims being made. In other words, we have the typical media circus that we find every time a new "missing link" is found.

For one thing, Luskin has just finished saying our models are wrong. The only reason that our models are wrong is because Ardipithecus ramidus isn't similar to other previously known fossils. That is why it is generating the buzz. The remains are completely, radically, different from the fossils that we have that come after, when bipedality is firmly established. The only reason it became part of a PR campaign at all is because it was so unusual. Hundreds of fossils have been yanked out of the ground in the last decade, none of which made the front page because they confirmed what we had already suspected about human evolution. Ardipithecus ramidus didn't. It suggested new things to think about and new models to work from. That is how science proceeds. Casey Luskin doesn't seem to like that.

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