Feb 17 2011

Lucy’s Feet

Lucy is one of the most famous fossil specimens of a human ancestor we have. It is a fossil of a female Australopithecus afarensis, a species that lived from 3.7 to 2.9 million years ago. This is soon after the split from our common ancestor with the chimpanzees (about 6-8 million years ago). It therefore tells us a great deal about the evolutionary forces that were shaping the hominid line.

One question of great significance is the extent to which A afarensis was bipedal. Was it bipedalism that defined the hominid line and made humans what they are, or was bipedalism a later adaptation?

The consensus has been that A. afarensis was indeed bipedal. This comes from multiple independent lines of evidence – the shape of the pelvis, the articulation with the femur, and details of the spine, for example. However, at the same time examination of the upper extremities reveals retained adaptations for life in the trees, such as strong curved fingers for gripping branches.

This makes A. afarensis a nice transitional species. We can easily imagine that this is a species that has partly come down from the trees and has evolved bipedalism in order to wander the expanding African savannah to hunt and scavenge. But at the same time these creatures were probably returning to the trees for shelter and safety. They are on their way to being fully bipedal, but have still not left the trees behind completely.

One question that has remained open was the anatomy of A afarensis feet – how adapted were they to bipedalism? The more similar they were to modern human feet, then the more time it is likely that A. afarensis spent walking rather than swinging from branches.

A newly published analysis of a 3.2 million year old afarensis fourth metatarsal (foot bone), in conjunction with examination of other afarensis foot specimens, indicates that A. afarensis likely had arched feet. An arched foot is a key adaptation to bipedalism and is a marker of the hominid line. The authors report:

A complete fourth metatarsal of A. afarensis was recently discovered at Hadar, Ethiopia. It exhibits torsion of the head relative to the base, a direct correlate of a transverse arch in humans. The orientation of the proximal and distal ends of the bone reflects a longitudinal arch. Further, the deep, flat base and tarsal facets imply that its midfoot had no ape-like midtarsal break. These features show that the A. afarensis foot was functionally like that of modern humans and support the hypothesis that this species was a committed terrestrial biped.

Pretty cool. This new find supports the other lines of evidence that A. afarensis was not only bipedal, but was committed to bipedalism.

For laughs I like to see what the creationists have to say (if anything) when a new find like this is published. I was referred to Ken Ham’s Answers in Genesis page. The discussion of this news item was particularly weak, which is saying a lot given the ordinarily thin standards of creationist propaganda. I can sum up the entire intellectual content of Ham’s analysis in two words: “Oh, yeah!”

He writes:

Scientists have pointed out that most of Lucy’s features, especially her head and jaw, are distinctly apelike, with wrist bones suggesting she walked on all fours. These observations are difficult to reconcile with the claim that her pelvis and leg bones are evidence of upright walking, although creationists have attacked that claim as speculative. And, of course, the general incompleteness of Lucy’s skeleton casts doubt on the certainty of any interpretation.

This is not hard to reconcile at all – Lucy has a mixture of ape-like and human features because she is part of  the way evolutionarily between our ape common ancestor and humans. Lucy is what all creationists dread and try desperately to deny, a transitional fossil.

Ham also characterizes the Lucy specimen as incomplete. While this is technically true in that all fossil specimens are incomplete, Lucy is actually a relatively complete specimen. That is part of what makes Lucy famous. She is complete enough that she provides a great deal of fossil information, but Ham would have you believe she is a poor specimen that “casts doubt on the certainty of any interpretation.” This is classic denialism.

Take a look at the picture of the Lucy fossils. This is a fabulous specimen. Also keep in mind the bilateral symmetry of the human body – so every bone can be reflected in the other side. For example if we found a specimen that was the entire left side of a hominid, only 50% complete, that would be as good as a 100% complete specimen.

And Lucy is not the only afarensis specimen we have. There are many specimens, including one rich site in Ethiopia, AL 333, with over 200 bones from an estimated 17 individuals. This is the source of the metatarsal bone in the current analysis, along with 35 other foot bones.

Of course paleontology is an inexact science that attempts to make the best inferential reconstruction of the past from incomplete data. It is like a horrifically complex puzzle and we don’t have all the pieces. There is therefore room for contrary opinions and doubt. But that is not the same thing as saying that we know nothing and does not allow for the evidence we do have to be brushed aside.

The denialist strategy is to exaggerate doubt and declare any evidence as being insufficient. Ham writes:

As with many high-profile fossils, a layer of interpretation lies between what the creature was really like and our idea of what the creature was like. This interpretive layer thickens the less complete a fossil is, and Lucy is a perfect example of that. Even if australopithecines sported an arched foot, it does not mean they were our ancestors; even if the outer portion of some australopithecines’ feet were arched, it does not mean their entire foot was; even if certain foot bones were twisted in a certain manner, it only “suggests” the outer portion of their feet was arched; and so on—at each step, the scientists have made a jump from the evidence to the conclusion. Moreover, how partial and interpretation-laden are the 35 fossils used in this analysis, and how certain is their connection to Lucy?

The is pure denialism. The fact is we have a large amount of hard and compelling evidence. This allows us to make some very confident broad brush-stroke conclusion – for example that humans and modern apes share a common ancestor, that the hominin line leading to modern humans has been evolving from our common ancestor for 6-8 million years, and that bipedality was an early adaptation of our line. As we try to make finer and finer details claims, it gets more tricky, and we need more lines of evidence (and always more specimens) to resolve differences of interpretation.

But uncertainty at the finer levels of detail does not call into question the big picture. That again is a denialist strategy – focus on tiny details as if they cast doubt on the big picture.

Ham also ignores the massive problems that the A afarensis specimens represent for the young-earth creationist position. According to that mythology there is no reason for a creature like A. afarensis to exist at all. But evolution predicts that a species like A afarensis should have existed at some point in the past few million years. What exact twists and turns evolutionary history actually took is still a matter to be determined, slowly, as we accumulate more specimens. But something with a mixture of human and ape features had to exist in the past if humans share a common ancestor with apes, as evolution predicts.

Ham’s caviling in nothing but pathetic denialism. Meanwhile, paleontologists continue to pull more and more fossils out of the ground, each one a little validation of the fact of evolution while teaching us more about the small details of the course of evolution.

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9 responses so far

9 Responses to “Lucy’s Feet”

  1. HHCon 17 Feb 2011 at 4:05 pm

    Given the pelvic, knee, and foot structure of Lucy, would she most likely lunge forward instead of using conventional walking steps?

  2. sonicon 17 Feb 2011 at 8:18 pm

    Of course one could look to modern studies of foot biomechanics to get a second opinion on these proclamations (warning-long article)–
    http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0014432

    A good summery as it applies to this situation-
    http://content.usatoday.com/communities/sciencefair/post/2011/02/paleontology-lucys-feet-made-for-walking/1

    “…interpretations of the function of the early hominin foot based on morphology of even partial feet, let alone single bones, are likely to be unreliable and certainly ungeneralizable to species level.”

    So it seems Hams analysis of the situation with regards the interpretation of the foot function based on a single bone is in agreement with the current science.

    I believe it would be illogical to conclude that ‘pathetic denialism’ is synonymous with correctness in all cases.

  3. HHCon 17 Feb 2011 at 8:57 pm

    If Lucy’s spinal development resembles Scheuermann Disease then lifting, climbing, and acrobatic activities would be dominant daily activities.

  4. Myk Dowlingon 18 Feb 2011 at 1:10 am

    @sonic, your reading of the Reaction Roundup seems a bit biased.

    ” The paper’s bottom line is that the species “was a committed terrestrial biped.” Agreed. Despite a whole host of analyses purporting to show otherwise over the decades, that is what the original interpretation (made largely Owen Lovejoy and colleagues) was when we named this species in the late 1970s. ”

    – paleoanthropologist Tim White of the University of California, Berkeley

    This seems a fairly ringing endorsement, as does this one:

    ” This is a great piece of work; fossil foot bones are very rare which is why many of us have started to look at fossil footprints so any new discovery is really exciting. The work clearly shows that A. afarensis had lost many of the characteristics associated with apes and was well on the way to having a fully modern foot function. The next key step is to understand what happened around 1.5 million years ago when we get the transition to Homo and endurance walking and running. ”

    – environmental geologist Matthew Bennett of the United Kingdom’s Bournemouth University

    Out of three comments, you have leaped on the only one that casts doubt.

    Crompton’s reference to Lucy’s possible asymptotic flat-footedness doesn’t really seem relevant to this new work based on fossils other than Lucy.

  5. BillyJoe7on 18 Feb 2011 at 4:33 am

    Sonic,

    “So it seems Hams analysis of the situation with regards the interpretation of the foot function based on a single bone is in agreement with the current science.”

    That was the opinion of one scientist.
    The other two scientists whose opinion was quoted agreed with the interpretation of bipedalism on the basis of the anatomy of the 4th metatarsal.

    So it seems to me that it is a bit of a stretch to say that “Hams analysis … is in agreement with the current science”.

  6. Steven Novellaon 18 Feb 2011 at 8:05 am

    Of course there are dissenting opinions among scientists. That’s part of the process.

    The pathetic denialism is in pointing to the inevitable dissent and arguing that it means the science is worthless, or just to sow as much doubt and confusion as possible. Denialism is all about spreading doubt – and not the good kind of doubt that leads to investigation, but knee-jerk doubt just to deny the science.

    Further, the denialism is in the argument that because there are disagreements about the tiny details, that the big picture of evolution is in doubt. The bigger implication here is that we have fossils of half-apes, half-humans – whatever the details are about how developed A. afarensis bepedalism was.

  7. sonicon 18 Feb 2011 at 3:57 pm

    Dr. N.-
    First- sorry for the tone of that last.
    It’s just that a couple days ago you wrote such an excellent piece about preliminary studies. It seems this is a case where the researchers don’t know the latest about foot function (why would they- the research is very new) and are making statements that go well beyond what the evidence will bear.
    As to what Ham says-
    ‘…the general incompleteness of Lucy’s skeleton casts doubt on the certainty of any interpretation.’ is exactly in alignment with what the foot anatomy experts seem to be saying.
    It seems you want to make a bigger point about evolution or denialism. That is fine- I’m just questioning this as a good example.

    Myk Dowling, BillyJoe 7–
    I am biased by the fact that of the three comments one is based on the best current understanding of foot function and how it relates to anatomy, the other two comments are not. This is about foot anatomy and conclusions one can draw from evidence-

  8. BillyJoe7on 19 Feb 2011 at 4:33 am

    Sorry, I didn’t see Myk Dowling’s response, which makes mine superfluous.

  9. HHCon 28 Feb 2011 at 2:11 pm

    Lucy could mostly lunge/ walk, sprint, lift, and do acrobatics while climbing. Being a female, she had to frequently choose the flight pattern of the “fight or flight” adaptation.

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