Ardi: Looking at the Latest Missing Link

Virtually everyone with any access to news last week probably heard about Ardi, a 4.4 million year old skeleton of a human ancestor found in Ethiopia. However, given the tendency of the mainstream media to cover every ancient primate discovery as “Scientists discover ‘missing link’ which ‘changes everything’” those who don’t track these things can easily become confused, or even rather suspicious of the whole thing.
So, what is Ardi, and why is this discovery a big deal?

Ardi is a 45% complete skeleton of a female individual from the hominin species Ardipithecus ramidus. This is not a new species: we’ve known about Ardipithecus ramidus since a small number of bones from a member of the species was found in 1992 and formally described and named in 1994. Living about 4.4 million years ago, Ardipithecus ramidus is also not the oldest human ancestor known or a common ancestor between humans and our apparent closest genetic living relatives, the chimps. However, the excitement about Ardi (found along with less complete remains of a number of other Ardipithecus ramidus individuals and also fossil evidence about the plants and animals present in their environment) is not just hype. It is a very important find. Here’s why:

Very Complete, Very Old
Invariably, Ardi has been compared to the other famous hominid find, Lucy who made headlines back in the 70s. However, Ardi is both more complete than Lucy and also over a million years older. Lucy was a 40% complete skeleton, about 3.2 million years old, belonging to the species Australopithecus afarensis.

We have a few fossil finds from hominid species which are older than Ardi, but we don’t know nearly as much about these species because the finds are much more fragmentary. Sahelanthropus tschadensis lived 6-7 million years ago, but the only fossils found so far of it are a partial skull. Orrorin tugenensis lived 6 million years ago, but all we have is a leg bone and a few fragments. So while basically all we know about these earlier species is that we have a few scraps of bone from a creature that looks to be a hominid and doesn’t belong to any other known species, we now have a very clear idea of what Ardipithecus ramidus looked like, and thus what hominids living 4.4 million years ago were like.

A Missing Link
Is Ardi a “missing link”? Well, she (and the other remains found in the same place — much more partial remains of 35 other individuals) is certainly a missing link in the sense that these fossils provide us with a lot of fascinating information about a certain stage in hominid evolution. But there is no single “missing link” in the hominid ancestry chain. Fossils of primates in general are so rare that piecing together the more distant periods of human ancestry is very, very hard. While the charts we see in books and articles suggest seamless lines of descent, the actual evidence we have is often quite fragmentary, and even the links of the chain that we do have are often only partial. One stage or even a whole species may be represented by only a partial skull or most of a leg — enough to tell it’s different from known species, but not enough to have a very complete picture of the species. The below chart (excuse my poor freehand drawing skills) shows the problem, and why there’s often dispute among biologists as to where the actual branches are, and whether we’re descendants or cousins of some hominid species.
What is often referred to as “the missing link” is the hope of finding a species which appears to be a direct ancestor of both modern chimps and modern humans. Ardipithecus ramidus is not such a link, and indeed, some researchers are suggesting that Ardi points to that common ancestor being more ancient that previously believed.

What Ardi Tells Us
One of the most interesting things about Ardi is what she seems to indicate about human/chimp divergence. It had been widely assumed at one point that the common ancestor between humans and primates probably looked a lot like a chimp. Our DNA shows that we’re closely related to chimps, and because we often have difficulty not thinking about evolution in terms of “progress” (especially when we’re talking about ourselves) it’s natural to think of chimps as the “ancient” form and to talk about “humans evolving from chimps”.

Lucy knocked a bit of a hole in this thinking back in the 70s by showing that upright posture went back to Australopithecus afarensis 3+ million years ago, putting to rest the already crumbling idea that hominids prior to Homo erectus had been “knuckle draggers”.

Now we have Ardi, who despite having a big toe that would have allowed her to grip things thing her feet, has a pelvis and legs which are clearly adapted to walking upright 4.4 million years ago. Even the leg bones we have from Orrorin tugenensis 6 million years ago appear to suggest a bi-pedal posture (though it’s harder to know from such incomplete remains). So with Ardi’s well preserved skeleton for confirmation, it’s starting to look very much like human ancestors have been bipedal for a very long time. Large brains and other adaptations are later, but it would appear that it may have been the chimps and gorillas who developed adaptations for arboreal life, and in the process shifted to walking on all fours and putting weight on the knuckles of their hands — rather than these being features that our ancestors shed.

Ardi did have proportionally much longer arms than more modern human ancestors, and her fingers were long for gripping branches. Her feet could still grip better than ours can (though not as well as modern great apes). Her brain was about the same size as that of a chimp, and she stood about four feet tall (the height of my seven-year-old.) But while she probably did not possess any of the traits that we see as uniquely human (language, higher consciousness, reason, complex tool-making, etc.) she looked less “like an ape” than expectations would have been in the past.

For more detailed information, the following are interesting links:

At long last, meet Ardipithecus ramidus

Ardipithecus: We Meet At Last

And if you really want the mother lode, the journal Science (which put out a special issue with all the original research papers on Ardi) has taken the unprecedented step of making all of the papers available on their site if you fill out a free registration. The Science Magazine Ardipithecus site is here.

12 Responses to Ardi: Looking at the Latest Missing Link

  • Tito Edwards says:

    Another point that needs to be made is the highly inaccurate art of dating these fossils. Combine that with the fact that you can never find one group of geologists and/or geneticists to even agree with either anthropologists and/or archeologists.

    For example, Lucy’s bones were found within a 32 square mile radius. What kind of science is that?

    I can find a chupacabra within a smaller radius just by piecing together dog and chicken bones together.

    Just my two cents worth.

    Oh, and don’t get me started on carbon-14 dating.

  • American Knight says:

    It is almost like someone very, very intelligent wrote the DNA code that created human animal bodies (like a single pair) for a human soul to be infused into and in that wisdom allowed nature to take its course and develop cousins who only have a corporeal soul to animate them. Hmm. Makes you think.

    Nah, that sounds like a fantasy. It is obvious that a random, infinite universe accidentally manufactured life and that undirected life evolved from amino acids into human beings who other than being smarter are no different than other animals. That makes much more sense. Randomness, yeah, thats far more rational so it must be scientific.

    Thanks for posting that. I was curious and I think there is a show on Discovery or National Geographic. It piqued my interest but I dread watching becuase they paint evolution infallible and prove the Law of Evolution before they can even postulate something probable for the origin of life. I’m lazy and it takes too much effort to pull the facts out from their nihilistic fantasy.

    It irks me being caught between neo-pagan ‘scientists’ and young-earth creationists. As if God isn’t wise enough to develop evolution and wait 15 billion years for Adam and Eve.

    Do you ever feel insane becuase ‘intellectuals’ think you are a superstitious troglodyte and fundementalists/evangelicals think your an apostate?

  • e. says:

    Do you ever feel insane becuase ‘intellectuals’ think you are a superstitious troglodyte…

    In the Words of The Great Picard:

    “Horrifying… Dr. Barron, your report describes how rational these people are. Millennia ago, they abandoned their belief in the supernatural. Now you are asking me to sabotage that achievement, to send them back into the dark ages of superstition and ignorance and fear? No!

  • Anthony says:

    Picard has 3 bad Star Trek movies to his name and 1 good one. Kirk is good even in bad Star Trek movies. :)

    Fascinating read. Thanks for the post, Darwin.

    I’m happy to discover from the above drawing that it appears the makeup in the original Planet of the Apes may actually not be that unrealistic.

  • e. says:

    Actually, the Planet of the Apes movies (as opposed to its incredibly inferior reincarnated version on TV) were quite thought-provoking.

    Just one of many interesting questions it raised: would it be considered ethical to kill Hitler when he was a child knowing full well the horrors that would inevitably result if he were allowed to live?

  • Blackadder says:

    e,

    I’ll admit it’s been a while since I’ve seen the Planet of the Apes movies, but I don’t recall there being anything in there about killing Hitler as a child. Which of the films are you thinking of?

  • Tito,

    The Hadar formation where Lucy and the remains of a number of other australopithecus individuals were found is pretty large, but the accounts I’ve read of the find have all indicated that all the bones from the individual nicknamed Lucy (the one 40% complete skeleton) were found in close proximity in a single gully.

    It’s true there are certain controversies regarding dating, but honestly you’re not generally going to see huge reversals on these thing. At this point, stratography-based dating is pretty good in most areas.

    American Knight,

    Well, I’d want to point out that “random” in the scientific sense doesn’t make a philosophical or theological statement as to whether something is intended or created by God, it just has to do with whether it’s predictable. So God’s providence and “random” evolution are not necessarily at all contradictory.

    But yes, it does get really old on the one hand trying to explain scientific findings to other Christians, and on the other hand having a bunch of New Atheist scientists in the background howling that science has disproved God.

    I suppose the bright side is that we’ve been dealing with this kind of silliness ever since St. Augustine’s time. He talks about the same conflict in Confessions, and Galileo quoted him in his letter to the Grand Duchess Christina.

  • e. says:

    I believe it was the last one, if not, the one before the final one.

    From what I vaguely recall, they were attempting to make a decision whether or not to kill the offspring of the two parent apes, who was said to be the very one that would bring about the future world where apes were rulers of men.

    It was, I believe, some general who attempted to make the analogy of whether it would be right to kill Hitler if he were only a child.

    Obviously, he was endeavouring to draw a parallel between the would-be leader of the future world of Apes who would conquer man to Hitler.

  • e. says:

    Blackadder:

    Just found it!!

    It was “Escape from the Planet of the Apes”:

    ESCAPE FROM THE PLANET OF THE APES
    *** (out of four)
    DVD Grades: Image A Sound B

    Arguably the most dated franchise entry (in terms of production values), Don Taylor’s Escape soars regardless, thanks to fine performances, the touching couplehood of Cornelius and Zira (McDowall (returning to the role after his absence in Beneath) and Hunter disappear into the make-up more than ever before), and a thought-provoking climax that carries genuine tragic weight.

    Whaddya know, another downed spacecraft! Cornelius and Zira exit Taylor’s repaired vessel only to find themselves in present day America. Initially the toast of champagne society, the media quickly turns on them when details of Taylor’s fate surface through interrogations.

    A shady Washington official (Eric Braeden) moves to sacrifice Zira’s child upon birth, arguing the Hitler clause (as in, knowing what you know, would you murder Hitler in his youth?), a predication that masks inter-species racism–er, specism?

    SOURCE: http://www.filmfreakcentral.net/dvdreviews/plotaevolution.htm

  • e. says:

    DarwinCatholic:

    But yes, it does get really old on the one hand trying to explain scientific findings to other Christians, and on the other hand having a bunch of New Atheist scientists in the background howling that science has disproved God.

    When confronting Protestants (in my own immediate experience, Evangelicals in particular), it would be prudent to simply take the Catholic Church’s stand concerning Faith & Reason and not yield to their cries of Apostasy simply because we Catholics are broadminded enough to consider the fact that scientific truth need not contradict Truth itself.

    A similar event in our historical past should prove a very apt & cautionary tale:

    The heliocentric model posited a moving Earth orbiting the sun just as the other planets did.

    Although viciously attacked by Protestants for its alleged opposition to Holy Scripture, the Copernican system was subject to no formal Catholic censure until the Galileo case… (p 69)

    The Church, sensitive to Protestant charges that Catholics did not pay proper regard to the Bible, hesitated to permit the suggestion that the literal meaning of Scripture – which at times appeared to imply a motionless Earth – should be set aside in order to accomodate an unproven scientific theory. (p 72)

    SOURCE: http://books.google.com/books?id=zVDR2ZePzvUC&pg=PA69&lpg=PA69&dq=thomas+woods+how+the+catholic+church+built+western+civilization+galileo+protestant&source=bl&ots=JeHccIr-iK&sig=4DG0lgRSw-xJntSnaxA4usYc3EI&hl=en&ei=MW_OSve1G5fymwOipYX9Ag&sa=X&oi=book_result&ct=result&resnum=3&ved=0CA0Q6AEwAg#v=onepage&q=&f=false

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