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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Rich - #48266

January 19th 2011

Martin (continuing):

The tacit anti-Catholicism I spoke of (which I was careful to qualify as a thematic anti-Catholicism implicit in certain inadequate histories of the Church, not a personal animus against Catholic people on your part) is exhibited in this statement of yours:

“As a Protestant, I believe that aberrant beliefs and practices entered the church early on,  leading to a corruption of the church’s doctrinal purity.  This led to the misguided elevation of the Apocrypha to the level of inspired Scripture ...”

This portrait of early Church history, in which the first few generations of followers retain their doctrinal purity, and then fall inexplicably into semi-pagan darkness and error, producing the dastardly “Catholic” Church, which misleads the faithful for 1400 years until the heroic Reformers come along and bring back the glory days of the early Church in warm, loving places like Geneva (!), has always been beloved of anti-Catholic polemicists.  But as Church history, it’s complete rubbish, and no serious Protestant Church historian nowadays associates himself with such propaganda.  It is disconcerting to learn that there are still Protestant pastors who believe and promote such crudities.


Rich - #48268

January 19th 2011

Martin (concluding with some specific points):

A.  Major Premise [provided by Martin Rizley]:

“What cannot be demonstrated from the Scriptures to be true cannot be imposed on the conscience as divinely authoritative.”

Minor Premise [empirical fact]:

The Protestant canon of Scripture “cannot be demonstrated from the Scriptures” to be the correct canon.

Conclusion:

The Protestant canon of Scripture “cannot be imposed on the conscience” of Protestant churchgoers as “divinely authoritative.”

Better be careful about your premises, Martin.

B.  “Do you see why there must be some ‘highest authority’ which acts as the final arbiter of truth claims made by any church or by any church leader?”

Yes, I do; but unfortunately, that highest authority cannot be Scripture alone; for Scripture requires interpretation, and interpretation is done by fallible humans, and fallible humans differ over the meaning of Scriptural passages; and since no Church can survive with conflicting interpretations of Scriptural passages (where those passages are of central import for faith or morals), there has to be an authoritative *interpreter* of Scripture.  That interpreter is the Church, understood collectively.


Martin Rizley - #48269

January 19th 2011

Rich,
So as not to prolong unduly this dialogue—since it has deviated just a bit from the issue of bipedality in the fossil record!—I will make two final comments.  You can respond if you wish.  You say, “I have written of “Church” to mean the authoritative tradition of Christians Yet the various groups you mention—the Anglican Church, the Greek Orthodox Church, the Coptic Church, the Lutheran Church, the Reformed Church—differ so widely from each other on so many points of doctrine and practice, that it seems almost ludicrous to speak of one “authoritative tradition” which they share in common.  Where is this elusive tradition that you speak of, defined by no church in particular, but shared by all?  It seems that instead of one authoritative Christian tradition, one has to speak of various ‘traditions.’  The question then is, how do we know which tradition is most closely in line with the teaching of Christ’s apostles, and that requires a ‘higher standard’ by which to make that judgment.  (continued)


Martin Rizley - #48271

January 19th 2011

You also say, “Certainly if the Church—any Church, not just the Roman—is not infallible *at least* in its judgment concerning the canon, it will mislead its people, either by offering them false Scriptures, or by failing to provide them with a complete set of the true ones.”  A church which does not claim to be infallible in its decrees is not misleading people with false claims.  If it claims that God has given to it by special revelation an inspired ‘list’ of books which are canonical, then it is misleading people.  But no Protestant church makes that claim.  Rather, every Protestant church acknowledges its own fallibility as a church and the fallibility of its decrees.  Nevertheless, as a confessional body, it says, “Despite our human fallibility, we nevertheless believe and confess that these 66 books, and these only, are those to which the Holy Spirt has borne incontrovertible witness concerning their inspiration by God.”  Since Jesus taught that those who are willing to do His will be given spiritual discernment, those churches .which are most devoted to the apostolic gospel are the least likely to err in recognizing the limits of the canon.


Rich - #48277

January 19th 2011

Martin:

Oh, goody; I get the last word.

I never suggested that all of the Churches named shared the same traditions, doctrines, practices, or anything else.  I said that what they all had in common was that they all looked to *both* Scripture *and* the mind of their own Church (understood as in succession to the apostles) as authorities.  Even the Reformed and Lutherans do this, and even the free churches who pretend to a more radical version of sola Scriptura (though they, fooled by their own slogan, are generally unaware that they doing it).

You ask:  How do we know which tradition is most closely in line with the teaching of Christ’s apostles?  There is no non-circular answer to that question.  Any line of argument which anyone could possibly use to prove that Church X is more truly Christian than Church Y can always be shown, upon inspection, to bring in at least one (usually more than one) assumption that cannot be derived from Scripture.  All Churches of course use Scripture to prove that they are the true followers of Christ; but the way in which each Church reads Scripture is conditioned by different canons and different theological commitments, so there is no neutral confirmation of anyone’s position.


Jimpithecus - #48278

January 19th 2011

Martin wrote: “So as not to prolong unduly this dialogue—since it has deviated just a bit from the issue of bipedality in the fossil record!—”

Just a bit?  Ya think?


Rich - #48280

January 20th 2011

Martin (continuing from 48277):

Your claim that conservative Protestants champion a “non-absolute” view of the canon is ludicrous.  There is no “despite our human fallibility” preamble in, e.g., the Westminster Confession.  There is a list of 66 books declared to be Scripture, and a definitive statement that the Apocrypha are not part of Scripture—no ifs, ands, or buts.  I don’t see:  “We, your Church leaders who wrote this Confession, *believe* this is the canon, but gosh, we aren’t *sure*, so if you really really feel strongly that Revelation and James don’t belong, and want to refuse assent to all doctrines derived from them, that’s OK with us; and if you really really feel that 2 Maccabees should be included, and want to base a doctrine of purgatory on it, that’s OK with us, too.  We aren’t claiming to have had any divine revelation about this; we’re just regular guys doing the best we can.”

The Protestant affirmation of the canon is never made in such a spineless way.  The canon is treated as every bit as reliable as the doctrines of Incarnation, Trinity, Atonement, etc.  Indeed, without the firm conviction that the canon is flawless, all the other doctrines would be put in doubt.


Rich - #48283

January 20th 2011

Martin (concluding from 48280):

So we have an extra-Scriptural doctrine that the canon includes 66 definite books and no others.  All conservative Protestants accept at least this one extra-Scriptural doctrine.

You have only two choices for justifying your acceptance of this extra-Scriptural doctrine, Martin:  (a) “The wisest and most spiritual of my Church have researched this, thought it out, debated it, prayed about it, and decided on it by due process (approval of conferences, synods, etc.); it is incumbent upon me as a loyal member of the Church to accept the result approved by the leaders, who have apostolic authority”; or (b) “I don’t respect the authority of the duly appointed successors of the apostles to determine the canon; I decide which books are God’s for myself.  However, I personally feel that my Church has decided rightly, so I support the 66-book canon.  But if six weeks from now I think the book of James teaches works-righteousness, my canon will drop to 65.”

If you choose (a), you’re retracting your position regarding Church authority.  And if you choose (b), you have *zero* basis to condemn anyone who wants to excise 10 verses from Romans or any other part of Scripture.  Take your pick.


Martin Rizley - #48289

January 20th 2011

Rich,  I know I said I would give you the final word, but you’ll have to forgive me for responding to your last post.  There is a difference between being mistaken and being fallible.  A church may be firmly convinced that it is fallible—that is, capable of error, in principle—yet at the same time, be firmly convinced that it is not mistaken on some particular issue.  An individual Christian may say, “I know that I am personally fallible—capable of error—yet on this particular issue, I do not believe that I am mistaken, but have correctly discerned what is true.  Therefore, I will confess what I believe, not as something doubtful, but as something that is true.  That explains why all Protestant confessions state dogmatically that there are sixty-six books in the canon.  Because those churches are firmly convinced they are not mistaken on the issue of the limits of the canon.  Does a firm conviction that one is not mistaken on some particular article of faith add up to a claim of personal infallibility?  You may think it does; I disagree.  (continued)


Martin Rizley - #48290

January 20th 2011

The man born blind was not claiming personal infallibility when said in response to Jesus’ Messianic claim, Jesus “Lord, I believe.” He was simply confessing His faith, without reservation or qualification.  So to say “There are sixty-books in the canon” is not a claim to personal infallibiltiy.  It is a confession of faith, of strong, Spirit-given conviction.  The voice of faith always says,.  “I believe; therefore, I speak.”


Rich - #48306

January 20th 2011

Martin:

Thanks for clarifying what you meant, but it doesn’t advance the discussion, because I never once used the word “infallible” (an apparent obsession of yours) to describe the Protestant position on the canon or to describe anything else.  You may have thought that I was promoting or defending some conception of “infallible” authority, but I was not.  I was talking about everyday authority, “authority” as the word is used by normal people.  We say that someone has authority over something because he has been entrusted with the *power to decide*, not because he always makes correct decisions.  It’s correct to say that the leaders of the Church had authority over the canon, since, being in direct apostolic succession, they had the responsibility to ascertain which books were inspired and which were not, and the power to make their decision binding.  In Protestantism they exercised this authority to establish 66 books.  In other Churches they came up with more.  It is immaterial to my argument which Church picked the books that God wanted.  The canonical buck has to stop somewhere, and it stops with the Church.  Which Church chose rightly is known only to God.


penman - #48336

January 20th 2011

Martin Rizley #48230

=Sola Scriptura says that while tradition—in the form of creeds, confessions, commentaries, etc.—may be helpful in clarifying the meaning of the Scriptures, since godly people have been reflecting and meditating on the meaning of the Sciptures for centuries, tradition is always subject to judgment by some higher, overruling authority which judges the value of that tradition and the faithfulness and teaching of every church leader— and that higher, overruling authoirty is the Scripture itself.=

I don’t see how that’s going to work. It leaves us with the same question we started with: how do we know what the higher, overruling authority says? We’re left with the task of INTERPRETATION. And it’s no part of catholic, Lutheran, or Reformed teaching that one can extract onself from the historic believing community & deliver personal or sectarian interpretations as authoritative (although one can hold them privately, on matters outside the “rule of faith” in the creeds).

I lean more to Martin’s view on the coherence of scipture, but I think Rich is right to keep pointing out the dangers of uncritically identifying a narrow YEC Protestantism with the “clear” & “obvious” teaching of scripture.


James Foard - #73052

September 24th 2012

Thank you for your forum. I would like to respond on a few points to Professor Kidder’s statement that “it has become an article of faith for those espousing both the young earth creation (hereafter YEC) model and many who hold to the intelligent design model that transitional fossils do not exist and therefore evolution has not taken place.”

My first response is that this is not entirely an article of faith at all. YEC’s do not pull some kind of dogma out of their back pocket and ask their members to subscribe to it blindly. In fact, they often quote evolutionists themselves who admit as much, that transitional fossils are well nigh non-existent. Stephen Jay Gould, Eldredge & Tattersall, N.D. Newell, A. G. Fisher, Colin Patterson, and even Richard Dawkins have famously remarked on the paucity of transitional fossils, (see http://www.thedarwinpapers.com/MatthewstheInquisitor.htm).

My second point is that indeed, it would seem that Professor Kidder’s assertion is something akin to “the pot calling the kettle black”. When I read the literature, is looks to me as though it has become an article of faith for those espousing both the old earth creation (hereafter OEC) model and many who hold to the evolutionist model that transitional fossils do exist and therefore evolution has taken place.

My third point is that Professor Kidder’s illustrations of the anthropological “tree of life” and it’s “branches”, leaves much to the imagination. We all know, I hope by now at least. that 99.9% of this tree of life illustration does not exist; it was a fantasy even in Darwin’s day. The branches were penciled in to represent what was supposed to be millions of years of transitional forms, however all that we ever had were the tips and the roots of the tree; the “branches” had as much reality as Spocks ears do on Star Trek. 

Regarding human and ape transitional fossils, it looks as though Mr. Luskin has adequately addressed those issues in his book. I would also refer the reader to two chapters in my online book, The Darwin Papers, where this is discussed @ http://www.thedarwinpapers.com/oldsite/number9/Darwin9Part1.htm

and http://www.thedarwinpapers.com/oldsite/number9/Darwin9Part2.htm

If the editors of this forum feel that these two chapters listed above may lack the academic polish worthy of most articles on the subject, they are free to omit the links if my response is posted.

James Foard

 

 


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