ResearchBlogging.orgi-68d5312667866fe9103d6f046f7c6dff-orrorin_hip.jpgThe ape human split is a bit of a moving target. In the 1970s and early 1980s, there were geneticists who placed it at very recent (close to 4 million years ago) and palaeoanthropologists, using fossils, who placed it at much earlier. During the 1980s, the ape-human split moved back in time because of the importance of sivapithecus, then later in time when Sivapithecus slipped and fell out of the hominid/hominin (human ancestor) family tree. Meanwhile the geneticists were moving towards a more and more recent split. At one point not too long ago, all the evidence converged with the split being around five million years ago. The fossils and the genes agreed, and there were rumors (but nothing published) saying that palaeoanthropologists working in Ethiopia were prepared (soon) to announce that one of the fossils dating to this time had “less then fully developed” bipedalism.

But science marches on, and the kinds of questions we are asking of the human fossil record are more detailed than the fossil record usually gives up in a mere few decades of research. So new finds came along and everything changed again. Now, there is a new paper by Richmond and Jungers suggesting that one of the earliest hominid, Orrorin tugenensis, was just as bipedal as any australopith, yet is much farther back in time than, and in many ways, different from our genus (Homo).

The new finds that changed things included this hominid, discovered some time ago, as well as material recovered in Chad. These early hominids pushed the ape-human split back to closer to seven million years or more. The present paper provides a detailed analysis of the mechanics of bipedal locomotion in Orrorin.

From the paper in science:

… femora discovered in Kenya and attributed to Orrorin tugenensis, at 6 million years ago, purportedly provide the earliest postcranial evidence of hominin bipedalism, but their functional and phylogenetic affinities are controversial. We show that the O. tugenensis femur differs from those of apes and Homo and most strongly resembles those of Australopithecus and Paranthropus, indicating that O. tugenensis was bipedal but is not more closely related to Homo than to Australopithecus. Femoral morphology indicates that O. tugenensis shared distinctive hip biomechanics with australopiths, suggesting that this complex evolved early in human evolution and persisted for almost 4 million years…

The key result here is that one thing we already knew to be true … that early hominids had a form of bipedalism that was different than modern humans (or other, earlier members of our genus), and that many different species of had this feature, and that it was an adaptation that lasted a very, very long time. Now we continue to think that this is true, but with an added two million years or so of time.

Another key result is a salvo in the fight that has been going on among palaeoanthropologists. Certain features had previosuly suggested that Orrorin was similar enough to Homo that it, not the australopiths, was the “true human ancestor” … The present paper provided contradictory evidence. Orrorin is not more similar, according to these authors, to Homo than are the australopiths.

So what is the difference, or lack there of, that we are talking about? Look at the picture:

i-e9245debeb356013eb0187071f5d1c30-orrorin.jpg

It mainly comes down to one thing. Consider the hip joint to be the fulcrum of a lever. One arm of that lever goes out to the head of the femur, and the other arm goes out to some place on the pelivs. So the muscles that link your pelvis to your femur, which, among other things, move your legs around, are working across this lever system.

In australopiths and Orrorin, the lever arms are longer than in humans.

This means that greater force can be applied in the australopith-type hip than in the human-type hip in certain directions. Any of these earlier hominids would be noticeably different in their abilities in playing soccer than modern humans, on average. They would probably be better at both passing and scoring goals.

However, they would tire more quickly than modern humans, because a lot of soccer is about running back and forth and back and forth again and again without much else happening. Modern humans and our close relatives may be more efficient in walking and/or running over long distances than these earlier models of hominid.


Richmond, B.G., Jungers, W.L. (2008). Orrorin tugenensis Femoral Morphology and the Evolution of Hominin Bipedalism. Science, 319(5870), 1662-1665. DOI: 10.1126/science.1154197

Comments

  1. #1 Jim Thomerson
    March 27, 2008

    Modern thinking is that all the living (and fossil) great apes are in a single family, the Hominidae. So one should not be speaking of a human/ape dichotomy. As I understnd it, we think that modern humans are the sister group of chimps + bonobos. That we share a unique common ancestor not shared with other living great apes. Also there are various extinct lineages which are branches of the human lineage, and others which are branches of the chimp + bonobo lineage. If one is thinking cladistically, then identification of ancestors is impossible. All ancestors (nodes where branching occurs) are hypothetical. No cladist would ever say that some fossil creature was the ancestor of some living creature. One would rather attempt an analysis to determine where the branching point for the new fossil is in relation to other branching points.

    I think paleoanthropologists have been the group most reluctant to accept cladistics as a way of generating hypothesis of relationship. I’m not sure why this is.

  2. #2 Greg Laden
    March 28, 2008

    Jim,

    Some of the points you make are valid, but some are not IMHO. Any two living species can be said to have a common ancestor (as long as we have a single origin which so far has held up). If you extend your logic of humans and apes being in the same family because we need to have a cladistic view (if I’m understanding you correctly) and thus not having split, then humans and artichokes are also in the same family. There is without a doubt a tension between classification and phylogenetics in this area, and cladism is not a solution to that tension. (Nor is the system of classification that we use.)

    This may help make it more understandable: The term “ape” used in my post was not a taxonomic term. It was a word that means “one or more species of ape.” I could have used chimpanzee for part of that discussion but not for all of it, thus I used ape (see below).

    (Actually, I don’t meet very man cladists who really understand cladism from a philosophical or evolutionary point of view. Most cladists are mechanics. Have you read Hennig?)

    The extinct species that are called apes are probably best divided into two groups that have not been renamed formally because it is somewhat controversial. It is remotely possible that together they are not monophyletic with respect to other primates that are not called apes. Most of the named species of Miocene apes would not be in the same clade as the living apes (humans included).

    There is a chimpanzee-human split because there are apes and there are humans. Chimps and humans happen to be closest living sister taxa. I used the term “ape” because I was speaking about an historical framework in which a number of different species were being considered. In the early part of that thinking (and we are straying a great distance from the point of the post here) it was assumed that chimpanzees and gorillas were closest living sister taxa to the exclusion of human. Later in that historical framework that changed. Therefore, “ape” was the correct word.

    Palaeoanthropologists have embraced cladistics by and large.

  3. #3 Jim Thomerson
    March 28, 2008

    Yes, I have read Hennig. As you know, cladistics burst on the US scene in 1966 with the publication of Hennig in English. To cite Hennig is somewhat comparable to citing Darwin in terms of illustrating modern thinking (I am not sure which school of cladists I belong to these days). It took cladistics a while to catch on, in part because of the way it was presented to us old fogies (synonym for non cladist). Sarcastic references to the “Cladistic Religion” had more than a grain of truth. In any case, it was the late 90′s before I published my first cladistic analysis based on morphology (not supported by later DNA studies). So I have been a fairly reluctant convert.

    My professional work has been largely in fish taxonomy at the species to genus level. I am used to the Linnaean system and do not see that it conflicts with phylogeny. There have been a number of articles over the years addressing the issue. One issue is that a phylogeny may need more names for clades that those formally available. One solution is to create non-formal names to fill the gaps as needed. Another issue is that although species may be real, higher taxonomic levels are created by fools like me. This means that the amount of diversity in one genus may be greatly different than diversity in another genus, and so on. This gives a certain fuzziness to the practice of counting differences in numbers of genera, families, etc to compare diversities.

    Anyway, I understand what you are saying. Have you read Jared Diamonds’s “The Third Champanzee”?

  4. #4 Anne Gilbert
    March 28, 2008

    Hmmmmmm. . . . It sounds like Orrorin tugenensis wouldn’t have had the sort of problems I’ve been having lately(no, they’re not serious). I pulled a muscle in my hip on Tuesday. I was in an exercise class. It wasn’t pretty. Fortunately, I’m recovering at a fairly decent pace, and I will be going back to those exercise classes as of next week. But I doubt if O. tugeniensis would have had that kind of problem, by the sound of it!
    Anne G

  5. #5 Elizabeth
    March 28, 2008

    I think I had a step aerobics instructor named O’Tugeniensis … an Irish Girl … who really kicked ass.

  6. #6 David Marjanovi?
    March 28, 2008

    Modern thinking is that all the living (and fossil) great apes are in a single family, the Hominidae.

    This is not modern thinking, this is modern nomenclature. Nomenclature is not science, it is convention. The shape of the tree has not changed, we just apply the label Hominidae to another node in it.

    If one is thinking cladistically, then identification of ancestors is impossible.

    Well, proof that anything is an ancestor is impossible, but that’s not news — science cannot prove, only disprove. If something lacks autapomorphies and has the right age, it enters consideration for being an ancestor of what appears in the cladogram as its sister-group.

    I think paleoanthropologists have been the group most reluctant to accept cladistics as a way of generating hypothesis of relationship.

    No: entomologists (ironically), malacologists, conodont workers… both paleo- and neo- in the first two cases.

    I’m not sure why this is.

    The weight of tradition.

    To cite Hennig is somewhat comparable to citing Darwin in terms of illustrating modern thinking

    Exactly.

    (I am not sure which school of cladists I belong to these days).

    Are there any left? The pattern cladists have practically died out…

    This gives a certain fuzziness to the practice of counting differences in numbers of genera, families, etc to compare diversities.

    This is a drastic understatement. If you want to quantify biodiversity, you have to quantify biodiversity instead of trying to count the uncountable. I’ll post references to Faith’s Phylogenetic Diversity Index tomorrow.

  7. #7 Greg Laden
    March 28, 2008

    Hennig is available in English? SO much must be lost in translation….

    I’m preoccupied with some things that require that I not engage in this debate at this time. But I honestly do want to continue the discussion.

  8. #8 Jim Thomerson
    March 29, 2008

    Bad nomenclature is the root of all evil. Actually, I think botanists have been the most reluctant to accept cladistics. A large number of higher plant are clearly of hybrid origin, and cladistics does not deal well with clades of hybrid origin. It has been thought that hybrid origins were not very important in animals. This idea may be changing. So far as identifying ancestors, I see geneticists reconstructing ancestral genes, but know nothing of the methodology involved.

  9. #9 joe
    April 16, 2008

    With this evolution thinking, would it be right to believe that blacks are less evolved then whites as they still retain many of the ape like features?

  10. #10 Greg Laden
    April 16, 2008

    Joe,

    All human beings pretty much have the same exact features in common with the living apes (chimps, our closest living relatives). Whites have thinner enamel than blacks on average, which makes whites more chimp like. Also, Europeans have smaller brains relative to body size than some groups of blacks living in Africa and at least one group of Native Americans, so that makes whites more ape like.

    But these differences are all variations on an original theme that was in total derived from apes, so white people should not worry too much that they are more ape like than other kinds of people.

  11. #11 the real cmf
    April 16, 2008

    Joe: how are blacks, in your eyes, “more ape-like”?

  12. #12 Elizabeth
    April 16, 2008

    Joe, you are not serious, right? Please tell us that you are joking.