The Human Fossil Record, Part 2: Bipedality

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January 5, 2011 Tags: Human Origins

Today's entry was written by James Kidder. Please note the views expressed here are those of the author, not necessarily of The BioLogos Foundation. You can read more about what we believe here.

This is the second part of a series by James Kidder on the human fossil record. The first part can be found here.

One of the most fruitful and exciting areas of research in palaeoanthropology is the search for the last common ancestor to the higher apes and humans. This question is inextricably tied to concepts of what separates humanity from the animals around us. This is a question that has spiritual as well as physical ramifications. In this set of posts, we are dealing with what makes us human from a biophysical perspective.

Traditionally, paleoanthropologists have considered the hallmark of humanity to be habitual bipedalism. While we share many characteristics in common with the higher apes, this trait alone is practiced by no other animal. Some animals practice facultative bipedalism, allowing them to go short distances on two legs when necessary, but only humans use it as their only form of locomotion. Put a man on all fours and even a squirrel can outrun him. Bipedalism is a skill that we learn early in life, before we are sentient and even understand what makes us different from the animals around us. It is programmed into us.

Bipedalism is marked by a number of anatomical modifications to the standard primate body. These center on the pelvis and involve changes in the head (cranium) and the rest of the body (postcranium), reflecting a shifting of the center of balance from the abdominal cavity to the hip. In mammals, the hip is composed of three mirrored sets of bones: the ilium, the ischium and the pubis (Figure 1). The top part of the leg fits into the bottom-rear portion of the ilium, into a round socket called the acetabulum. It is one of two ball-and-socket joints in the body, the other being where the arm fits into the scapula at the top of your shoulder.

Where the two pubis bones fit together in the front and the two ilia meet in the back with the sacrum forms the birth canal. In chimpanzees and gorillas, the ilium is narrow and tall (Figure 2). Consequently, the connection to the upper leg bone, the femur, is straight up and down. In humans, the ilium is flat and flared, creating an outward bowing of the top of the femur, which allows for the balance necessary for walking upright (see Figure 1). This, in turn, creates what is known as the valgus knee, where the bottom of the femur meets the top of the large lower leg bone, the tibia, at an angle. The fact that the two bones meet at an angle provides for a better balance of the body mass for upright walking. In contrast, when higher apes such as gorillas and chimpanzees stand, the femur and the tibia are both perpendicular to the ground, resulting in a straight knee joint. Consequently, when chimpanzees walk upright, they swing side to side in an ungainly fashion to simulate the balance that is inherent in human walking.

Other changes are present above the hip, as well. Because they are quadrupedal, chimpanzees, gorillas and orangutans have a straight backbone, or vertebral column (Figure 3). In humans, the vertebral column resembles a double “s” shape, which balances the torso above the hip (and creates the back problems we suffer later in life). At the top of the spinal column, the top vertebra, the atlas, has facets that balance the head and the second vertebra, the axis, has a prong that fits directly into a hole in the skull. This hole, which is called the foramen magnum, is at the back of the skull in higher apes, as in all quadrupedal animals. This allows the animal to keep its head up while it is trotting along the ground. In humans, the foramen magnum is at the base of the skull, allowing us to look forward as we walk. It also makes it hard to look forward when we crawl on all fours. Each of these modifications is diagnostic of humans and easily recognizable in the fossil record in specimens for which these anatomical areas are present.

Ardipithecus ramidus and the Origins of Bipedality

The origins of bipedality have traditionally been understood as having evolved at the end of the Miocene epoch, around 6 to 8 million years ago (Crompton, Sellers and Thorpe 2010) when the climate began to dry out and cool. Unfortunately, there are only scattered presumed hominin remains from this time period, all of which are taxonomically controversial and fragmentary and none of which have diagnostic postcranial remains. It has also been thought that the transition to bipedality likely did not happen all at once but in mosaic fashion (as evolution often proceeds) and this has recently supported by the fossil record. Up until a few years ago, the most widely-accepted model was that bipedality originated among a group of large-bodied hominoids that had adapted to the savannah-jungle fringe. The jungle, itself, was ceded to the precursors of the modern chimpanzees and gorillas and the savannah to the precursors of the modern baboons and other terrestrial monkeys. As a result, some workers (Crompton et al. 2010) suggested that both arboreal (tree-dwelling) and terrestrial locomotion might have been present in our earliest ancestors. Recent evidence has corroborated some parts of this model, but not others.

In 1994, the remains of a remarkable hominin, dated to 4.4 million years ago, were unearthed in the Afar Triangle of Northeastern Ethiopia. Examination of the surrounding deposits, however, yielded a conclusion that this hominin lived in a woodland environment, rather than a savannah/forest fringe environment (White et al. 2009a). Requiring over ten years of extrication from the surrounding rock and painstaking reconstruction, this fossil form, Ardipithecus ramidus (now represented by 110 individuals) yields diagnostic parts of the pelvis (Figure 4), as well as sections of the arms and skull (Figure 5) (White et al. 2009b). Although the base of the skull is not preserved, one striking aspect of humanity is present in the teeth. The canine (eye tooth) does not extend beyond the tooth row. Humans are the only hominins for which this is the case. In all other ape species, fossil and extant, the canine projects well beyond the tooth row.

Biomechanics specialist Owen Lovejoy and colleagues (Lovejoy et al. 2009) write about this species:

“The gluteal muscles had been repositioned so that Ar. Ramidus could walk without shifting its center of mass from side to side. This is made clear not only by the shape of its ilium, but by the appearance of a special growth site unique to hominids among all primates (the anterior inferior iliac spine). However, its lower pelvis was still almost entirely ape-like, presumably because it still had massive hindlimb muscles for active climbing.”

Figure 6 shows the intermediate nature of the pelvis of Ardipithecus ramidus compared to later hominins (Homo sapiens, Au. Afarensis) and chimpanzees (P. troglodytes).

Ardipithecus, then, represents a shift away from the primitive locomotion employed by the last common ancestor of our line and that of modern chimpanzees. Here is a hominin that maintained a link with its tree-dwelling past and yet had progressed toward the bipedal future. This evidence is striking because it firmly demonstrates that a species had arisen that was advanced in the human direction. Whether or not it led to the hominin forms that followed is not known but it clearly represents a phenomenal example of a transitional form in the human fossil record.

From this point on, the forms become noticeably more human in appearance, leading eventually our own species some four million years later. In his infinite wisdom, God had set us on a path toward our eventual communion with Him. That this path took such a long period of time and through so many varied forms of humanity is a testament to His creative power and patience.

Next, the successors to Ardipithecus and true human walking.

Sources

Crompton, R., W. Sellers & S. Thorpe (2010) Arboreality, terrestriality and bipedalism. Philosophical Transactions of the Royal Society B: Biological Sciences, 365, 3301.

Lovejoy, C. O., G. Suwa, L. Spurlock, B. Asfaw & T. D. White (2009) The Pelvis and Femur of Ardipithecus ramidus: The Emergence of Upright Walking. Science, 326, 71, 71e1-71e6.

White, T. D., S. H. Ambrose, G. Suwa, D. F. Su, D. DeGusta, R. L. Bernor, J.-R. Boisserie, M. Brunet, E. Delson, S. Frost, N. Garcia, I. X. Giaourtsakis, Y. Haile-Selassie, F. C. Howell, T. Lehmann, A. Likius, C. Pehlevan, H. Saegusa, G. Semprebon, M. Teaford & E. Vrba (2009a) Macrovertebrate Paleontology and the Pliocene Habitat of Ardipithecus ramidus. Science, 326, 67, 87-93.

White, T. D., B. Asfaw, Y. Beyene, Y. Haile-Selassie, C. O. Lovejoy, G. Suwa & G. WoldeGabriel (2009b) Ardipithecus ramidus and the Paleobiology of Early Hominids. Science, 326, 64, 75-86.

Figure 1: http://www.bikemonkey.net/2010/01/3-series-tune-up-checking-the-pelvic-girdle/

Figure 2: http://www.boneclones.com/KO-303-P.htm

Figure 3: http://www.fixscoliosis.com/entries/13-The-Human-Spine-and-Idiopathic-Scoliosis

Figure 4: Bone Clones

Figure 5: National Geographic Images

Figure 6: from Lovejoy et al. 2009


James Kidder holds a Ph.D. in Biological Anthropology from the University of Tennessee (UT). He currently employed as an instructor at UT, and as a science research librarian at Oak Ridge National Laboratory. He has been involved in the Veritas Forum at UT and runs the blog "Science and Religion: A View from an Evolutionary Creationist/Theistic Evolutionist."

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Martin Rizley - #47220

January 14th 2011

Argon,  I don’t know enough about genetics to argue with what you’re saying on the basis of the data, I know that there are degreed biologists like marine biologist Dr. Robert Carter who would disagree with you.  He actually believes the genetic data can be interpreted in a way that supports the ‘bottleneck’ you say couldn’t possibly have generated the patter of genetic diversity presently found among human beings— http://creation.com/noah-and-genetics  I think the main reason why I remain unconvinced by scientific pronouncements that seem to contradict clear biblical teachings (clear to me, anyway) is that science, being based on human observation and deduction from a finite perspective, can never overcome the inherent fallibility which belongs to finitude, whereas the prophetic Scriptures, being sourced ultimately out of the infinite mind of God the Holy Spirit who ‘breathed out’ every word of Scripture, has a character of infallibility that is ‘no match’ for science.  If the Scriptures seem clearly to teach, therefore, that all modern humans have descended from one man (Acts 17:26), then I must believe that, even if I cannot explain the physical data that might SEEM to contradict that.


Martin Rizley - #47226

January 14th 2011

Jon Garvey,  I appreciate your taking the time to interact on this subject.  I would perhaps attribute more symbolism to the Genesis narrative than I do, were it not for two things:  1) the structure of Genesis itself as a flowing narrative involving genealogies which tie Adam to Noah and Abraham and the patriarchs—with no textual indication of a movement from ‘myth’ to history; 2) the perspective of the New Testament writers and their inspired commentaries on particular aspects of the Genesis narrative, which show a greater literalism in their understanding of Genesis than many modern moderns want to confess.  I find no away to get around the ‘historical’ implications of Paul’s theology at several points:  1) that sin entered the world through one man and one sin (how else can one explain Romans 5:16-19?); 2)  that God created one man, then subsequently created one woman from the body of that man;  3)  that all modern humans are descended from this couple;  4) that the world was created in a ‘very good’ state, but was later subjected to frustration, bondage and ‘groaning’ on account of man’s sin (in other words, it underwent changes).  These convictions hinder me from accepting neo-Darwinism.


Argon - #47229

January 14th 2011

I’m a degreed biologist too (biochemist, actually). Carter basically makes old arguments that don’t match observations about the rates and patterns of genetic divergence not just for humans but also in animals which would have survived on Noah’s Ark.

Martin Rizley - #47220: If the Scriptures seem clearly to teach, therefore, that all modern humans have descended from one man (Acts 17:26), then I must believe that, even if I cannot explain the physical data that might SEEM to contradict that.

Fair enough but that doesn’t mean one should accept the weak reasoning and poor science that currently characterizes most of the contradictory arguments (something Todd Wood rightly disparages).


Jimpithecus - #47239

January 14th 2011

Nedbrek writes in 47152: “So, if there were miracles involved in Creation and the Flood, science cannot investigate those events, right?  Jim, would you agree?”

Here is the problem: if God decided to create the world miraculously and create the flood miraculously, then He has done two things: He has covered his tracks inordinately well (He is God, after all) and he has also managed to create a HUGE body of evidence that a world-wide flood is exactly what did NOT happen.  It is not that there is a little bit of evidence for a world-wide flood, it is that there is contra-evidence.  That isn’t a miracle, that is deception.


Jimpithecus - #47240

January 14th 2011

Martin wrote in #47220 “If the Scriptures seem clearly to teach, therefore, that all modern humans have descended from one man (Acts 17:26), then I must believe that, even if I cannot explain the physical data that might SEEM to contradict that.”

Martin, why do you think God created the physical data that indicates a long creation and biological evolution?


Jimpithecus - #47241

January 14th 2011

Martin wrote in #47226 “I find no away to get around the ‘historical’ implications of Paul’s theology at several points:  1) that sin entered the world through one man and one sin (how else can one explain Romans 5:16-19?); 2)  that God created one man, then subsequently created one woman from the body of that man;  3)  that all modern humans are descended from this couple;  4) that the world was created in a ‘very good’ state, but was later subjected to frustration, bondage and ‘groaning’ on account of man’s sin (in other words, it underwent changes).  These convictions hinder me from accepting neo-Darwinism.”

In 50 A.D., Paul had no knowledge of quantum physics, geology, astrophysics, palaentology, radiometrics, biology, microbiology or the evidence that any of them have produced.  Why would he write differently?


Martin Rizley - #47246

January 14th 2011

Argon,  I’m not a geneticist, so I do not have the competence to judge the scientific merits of your arguments, as opposed to Carter’s.  Those why I, and other non-science people like myself, ultimately accept the Bible’s teaching about the past on ‘faith’  is because of its divine inspiration, which merits our implicit trust.  I notice that you mention “rates and patterns” of genetic divergence, which tells me that the science on which you rest your conclusions is based on the assumption that “the present is the key to the past.”  And that’s a fair assumption—for most of history.  However, I’m not sure it’s a safe assumption when it comes to those peculiar moments of history when God performed repeated miraculous interventions.  I believe in the economy of miracles, but I don’t think that means that God has done few miracles in history, but that there have been few MOMENTS in history when God did miracles in abundance.  The Exodus was one such moment;  as was the ministries of Elijah and Elisha, and Jesus and the apostles. So was the Flood and its aftermath—which means that the maxim ‘the present is the key to the past’ might not be a safe assumption during that unique moment in history.


Martin Rizley - #47248

January 14th 2011

Jimpithecus,
You say, “Paul had no knowledge of quantum physics, geology, astrophysics, etc. . . why would he write differently?’ 
In and of himself, neither did Paul have knowledge of the pre-existence of Christ, His incarnation as a human being,  the way of salvation of salvation through faith in Him, His future coming in judgment, heaven and hell, etc.  These things he knew only by divine revelation ONLY.  And the same God who revealed THESE things to him is certainly capable of revealing past historical truth to him, as well, such as the historical fact of Eve’s creation from the body of Adam, sin entering the world through Adam’s one sin, and the changes that took place in nature following the fall.  It is true that the Darwinian paradigm explains a lot of the physical data adequately and makes ‘good sense’ according to the canons of modern science.  But it does not take into account biblical teaching about the past, and that’s where(in my view) it goes wrong.  (continued)


Martin Rizley - #47250

January 14th 2011

Let’s say you walked past an apple tree on a windy day and saw a bunch of apples lying at the base of the tree.  While you were standing there, the wind blew and an apple fell from the tree in your presence.  What is the simplest, the most obvious theory that explains how ALL those apples ended up at the base of the tree?  Applying Occam’s razor (one of the canons of science), we would conclude the wind blew them all down.  What if I told you that instead a boy had plucked one of those apples and threw it down?  You would say that I was complicating the picture unnecessarily.  The ‘windfall’ explanation is the simplest and most obvious.  But if I picked up an apple and showed you that it had teeth marks on it, that might cause you to reconsider the adequacy of the ‘windfall’ explanation to account for all the data.  In my judgment, biblical teaching about what certain events in the past (such as the creation of Eve) are the ‘teethmarks on the apple” that the scientific community in its attempt to reconstruct human origins does not want to consider, because to do so would violate the canons of modern, secular science.


Martin Rizley - #47252

January 14th 2011

Jimpithecus,
As far as believing the Bible’s teaching AGAINST contrary evidence, is there not a sense in which God at time calls His people to do just that?  Look at Abraham when God called him to sacrifice Isaac.  Abraham knew that the cruel pagan gods of that day called for blood sacrifice.  His own autonomous judgment might have told him, therefore, that for God to ask such a thing of him proved that He was cruel. Either that, or God was ‘deceiving ’ him by asking him to do something that He would later put a stop to.  The test for Abraham’s faith was to believe that God really had commanded him to sacrifice Isaac, but that didn’t make God cruel or a deceiver.  To go on believing God, Abraham had to subordinate his own judgment to what He knew God was saying.  In like manner, God sometimes tests our faith by requiring us to go on believing in the truth of what He is saying, even though it may seem contradicted by the evidence, or may seem to cast a shadow on God’s character, as if He were out to deceive us.


Martin Rizley - #47254

January 14th 2011

In the end, Jim, both you and I must be faithful to what we believe God is saying in His Word.  You may believe that He is NOT saying what I think He IS saying—that ‘s why I am in no position to judge your heart, any more than you can judge mine.  Rather, both of us must seek to live in accordance with the understanding that God has given us to each one of us personally.


Jon Garvey - #47324

January 15th 2011

@Martin Rizley - #47226

There are models that accommodate all the key points of Pauline theology, as you know. But for the NT writers to handle the Genesis texts, whether or not they (or the Holy Spirit) were aware of symbolic, mythical or whatever elements that might be present, they still wanted to communicate the any truth in those statements to people who had never had reason to debate the matter of genre.

If I were drawing the truths from “Pilgrim’s Progress”, I would relate to the story as if it were factually true, rather than trying to explain at every turn, “Of course, there wasn’t really a man called Christian who met a giant; that’s just an allegorical fiction.” I’d be more likely simply to say, “what giants in our lives imprison us?” etc, because to a Christian, every element in the book truly relates to spiritual life.

That’s not to say that factual history isn’t important in these matters, but that using Scripture as God’s truth for spiritual teaching is a different activity from that of doing apologetics on the literal historicity of the text.


Martin Rizley - #47338

January 15th 2011

Jon,  I grant the fact that ‘we know in part,’ as Paul confessed in 1 Corinthians 13.  Even the apostles knew ‘only in part.’  I also grant the fact that symbolism occurs in the Bible, and that the OT prophets often saw the future substantial realities of God’s kingdom in terms of earthly types that foreshadowed them.  I am not a hyper-literalist with regard to OT prophecy.  I don’t believe that the temple will be re-built in Jerusalem, or the sacrifcial system will be re-instituted.  However, I believe it is grossly irresponsible, and in some cases, heretical, to relegate to the realm of symbolism what is clearly to be understood as historical fact.  A person who relegates Jesus’ resurrection to the realm of spiritual/theological only, and denies that the body that into the tomb Friday came out of the tomb in a glorified condition on Sunday, leaving the tomb empty, is not a Christian, no matter how religious he may be or how highly he may regard the ethical teachings of Jesus, etc.  Likewise, the person who denies the historical fall and the corruption and condemnation of all mankind in one man according to Romans 5 is, in my judgment, denying a “key point in Pauline theology.”  (continued)


Martin Rizley - #47342

January 15th 2011

I do not think one can make that denial without denying to some degree, the biblical teaching on the fall and a corresondingly ‘full’ understanding of redemption—for Paul wants us to understand in Romans 5 that sinners are ‘put right’ with God in the VERY SAME WAY that they were ‘put wrong’ with Him—that is, through the representative work of another who acts on their behalf.  Denial of the imputation of Adam’s sin and guilt—which follows from the denial of sin’s entrance into the world from one man—leads, in terms of biblical logic, to the denial of the imputation of Christ’s righteousness as the sole ground of our ‘right standing’ before God.  So I do not think that the denial of Adam’s historicity should be regarded as a minor matter.  It threatens the whole structure of a full-orbed, biblical theology on sin and salvation.  Moreover, it seems to me that Paul also strongly asserts that Christ redeemed the creation itself from a fallen condition by His death on the cross.  This, too, is a “key element in Paul’s theology.”  The creation will be set free ?God’s curse and from its bondage to corruption, implying that nature fell from an originally pristine condition, which Darwinism completely denies.


Jon Garvey - #47356

January 15th 2011

@Martin Rizley - #47342

The more I look at Romans 8, the more unlikely it seems that it is referring to the existence of death in the animal realm. I put some tentative thoughts down a few months ago, giving more questions than answers. Although my thinking has developed a little since then, I don’t believe it teaches a “pristine creation” (and neither does Genesis, which uses the word “good”, with a very different semantic range from “pristine”).

http://www.jongarvey.co.uk/download/pdf/Romans8.pdf


Martin Rizley - #47359

January 15th 2011

Jon,    I read your article, and I agree that nature’s slavery to corruption may include the fact of its ‘defilement’ through the shedding of innocent blood; surely, the earth will be liberated decisively from such defilement when Christ returns.  I also agree that life on a paradisal world would not necessarily involve the total absence of animal death and their resulting decomposition.  Francis Schaeffer made a distinction between ‘peaceful’ animal death (such as an old dog expiring by the fire place)—which he considered believed could have existed from the beginning—and nature being ‘red in tooth and claw’ through violent predation, which he saw as a natural evil resulting from the fall (a view that is suggested by the language of Isaiah 11:6-7, which indicates that there is something not quite right about violence in the animal kingdom—even if the language of the prophecy involves symbolism.) .  If Schaeffer’s theory is correct, there could have been carnivory from the beginning on a limited scale, if certain animals were created as ‘scavengers,’ but no predation.  (continued)


Martin Rizley - #47360

January 15th 2011

Genesis 1:29 would then be emphasizing the lack of predation in the pre-fallen world and the predominance of an herbivorous diet for all living creatures—not necessarily the total absence of carnivory in the form of scavaging.  What I find most difficult to reconcile with the Bible’s teaching is the view that violent predation and painful, degenerative diseases like cancer—both found in the fossil record—existed from the beginning in God’s ‘very good’ world.  Most of all, however, it seems to me that to deny any changes at all taking place in the natural world runs into serious difficulty with the fact that God is said to have ‘cursed’ the ground for man’s sake.  God didn’t simply make human life more difficult; He pronounced a curse on the ground itself.  The earth has come under a curse because of man’s sin.  Surely that is the background of Paul’s teaching in Romans 8 and his teaching in Colossians 1:20 on God reconciling ‘all things’ to Himself through Christ The earth needs ‘reconciling’ precisely because it fell under God’s curse.  If the earth ‘came under’ God’s curse, that means there was a time BEFORE that.


Martin Rizley - #47368

January 15th 2011

Jon
One further question.  I’m sure you saw the images from Haiti after the earthquake that devastated that country last year—the images of untold human suffering that resulted from the collapse of buildings burying people alive, crushing imbs, separating families.  The wailing, the crying that went up as a result of this disaster—can it be seriously suggested that these things would have been found in the ‘very good’ world that God made and beheld in Genesis 1:31?  Clearly not.  So however nature was affected by the fall, one thing is certain.  Prior to man’s fall into sin, individuals and communities would not have been devastated by natural disasters in the way the people of Haiti word.  Such tragedies are a testimony to the fact that we live in a fallen world, an abnormal world.  That tells me that modern scientific theories which ignore the biblical teaching and interpret the physical data in a straightforward manner according to the natrualistic, unifromitarian assumptions of modern science are bound to err..


nedbrek - #47370

January 15th 2011

Jimpithecus (47239) “Here is the problem: if God decided to create the world miraculously and create the flood miraculously, then He has done two things: He has covered his tracks inordinately well (He is God, after all) and he has also managed to create a HUGE body of evidence that a world-wide flood is exactly what did NOT happen.  It is not that there is a little bit of evidence for a world-wide flood, it is that there is contra-evidence.  That isn’t a miracle, that is deception.”

What do you believe is the greatest evidence against recent creation of the Earth, and a world wide flood?

Thanks


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