Homo floresiensis’ Primitive Wrist

I’ve done so much flip flopping on whether or not Homo floresiensis is in fact a new species of human over the last 3 years that I sometimes forget what opinion I currently hold. The only consistency in my debate has been the call for analysis of the other remains. It seems like I got my wish after catching last week’s Science publication of the The Primitive Wrist of Homo floresiensis and Its Implications for Hominin Evolution. The title is pretty self-explanatory.

H. floresiensis is a hominin found in 2003 from the Ling Bau cave on the island of Flores in Indonesia. The bones found are about 18,000 years old. There’s been a lot of back and forth discussion whether or not H. floresiensis deserves a new species. At first people thought it was a representative of H. erectus, then it was suggested that H. floresiensis is a primitive microcephalic modern human. I like many others held this opinion.

Earlier this year, Dean Falk did a comparison of the endocranial volume of the H. floresiensis skull, LB1, to a number of microcephalic humans, and primates. She found H. floresiensis to be uniquely different in size and morphology. For many that wasn’t enough because, we don’t have many microcephalic human skulls to measure and compare too.

The other bones found at the site are just as diagnostic, especially the bones of the wrist and hand. So what Tocheri et al. did was to use fancy 3-D methods to calculate all the different dimensions, areas, and angles of the trapezoid, scaphoid, and capitate bones and multivariate statistics were used to compare the Flores carpal bones to set of archaic and modern humans, Neandertals, australopithecines, gorillas, chimpanzees, and also OH 7 a.k.a. Olduvai Hominid № 7 or the type specimen for H. habilis. Here’s a quick run down on what they found.

The trapezoid is the main bone where the index finger’s metacarpal articulates with the rest of the wrist. It’s a small bone in modern humans. The Flores trapezoid is wedge shaped like humans but has a different orientation on the ulnar side. Here’s the figure they showed which illustrates LB1, Flores trapezoids, compared to the others.

Figure 1 - Tocheri et al., 2007 Trapezoid Comparison

The Flores scaphoid shape and articular surfaces are more triangular in shape and lacks the larger articular surface on the palmar side which is seen in modern humans and Neandertals. Curiously, the scaphoid also has a fused centrale; a condition seen in H. habilis.

The authors say this fusion is a primitive condition for all hominins, because in modern humans it is separate. But that is not entirely true. The centrale sometimes fuses onto the scaphoid as the tubercle of the scaphoid; but occasionally it stays separate. It is not as definitive as they authors are making it out to be.

Anyways, here’s the line up of the scaphoid comparison.

Figure 2 - Tocheri et al., 2007 Scaphoid Comparison

Last but not least, is the sweet capitate. The capitate is the largest bone in the wrist and it falls smack dab in the center. Aside from the size, I remember the capitate because it has a rounded head which reminds me of Captain Picard’s bald head. And no, I’m not a Star Trek fan… it just that this bone has a remarkable resemblance to his unforgettable head.

Parts of the capitate, like the head, look like a chimpanzee’s capitate. Check out the light blue part below. But others, such as the proximal surface (green part) resemble modern humans. All in all the authors say the articular facets and shapes are more primitive than not because of a “waisted neck” characteristic that I don’t know about.

Can you see it?

Figure 3 - Tocheri et al., 2007 Capitate Comparison

I must admit they have a pretty complete line up of capitates, and the images let us all see for ourselves how these three bones compare…

…But I wonder why they didn’t include microcephalic or even dwarf humans into the mix?

That’s my biggest complaint with this study. You’d think that they’d include them, considering the biggest competing hypothesis is the whether or not H. floresiensis was a bunch of small humans. I’ve never seen bones from a microcephalic’s or dwarf’s hand to say that their bones would be more primitive than not… but I would assume since dwarf skeletons are much more distorted they would have different morphological features.

21 thoughts on “Homo floresiensis’ Primitive Wrist

  1. Microcephaly (according to Roberts and Manchester, 2005, ‘The Archaeology of Disease):

    “has genetic or environmental determinants and is characterized by a statistically significant subnormal skull circumference and general severe mental impairment (the brain weight is considerably reduced). The frontal and parietal bones recede, the occipital bone is flattened and the cranial capacity is reduced to less than 1000cc, with a circumference of less than 46cm. In addition, the cranial sutures fuse earlier than normal and the face is larger compared to the rest of the head. Frequencies for microcephaly may be up to 1 in 2,000 births in isolated (inbred) populations.”

    They don’t say anything about the post-cranial elements. I don’t know whether that is because a) the effects are predominantly in the cranial elements and the effect on the post-cranial skeleton is negligible, or b) because they decided that identification in an archaeological context is most likely to be down to the skull rather than any other element. If anyone has a detailed description that includes what happens to other elements, I’d love to hear it.

    However, their description does raise the question of whether the ‘hobbit’ skull has the flattened appearance and so on that they describe. Does anyone know or is the microcephaly argument being mooted on the basis of cranial capacity alone?

  2. I know microcephaly has to do mainly with abnormalities in the head… but what I’m saying is they shoulda been a bit more thorough and thrown in a couple microcephalic carpal bones in to the comparison. See, the current debate is whether or not the Flores hominins were microcephalics or not… The authors even identify that in the beginning of the paper, so why not extend their analysis to the current debate? It seems like they just ignored it.

  3. Kambiz, you comment,

    “then it was suggested that H. floresiensis is a primitive microcephalic modern human. I like many others held this opinion.”

    On the other hand I was reasonably convinced it was a new species of small humans as soon as I heard of the discovery. Years before then evidence of occupation of Flores dating back 750,000 years had emerged. This was interesting because Flores is across Wallace’s line. Most mammals have been unable to cross this line yet here was evidence humans had done so long before it was thought they would have the ability to do so. Now it’s another biological rule that species on islands usually become smaller than their relations on the mainland. Examples are found all over the place: Mediterranean islands, islands off California’s coast (forget the name), Wrangel Island etc. So no surprise that a human species isolated on a small island for nearly three quarters of a million years would have evolved small size.

  4. I think perhaps you misunderstood my point, Kambiz. I am not suggesting that you were unaware that microcephaly is a cranial condition. What I was pointing out is that that condition is not diagnosed solely on cranial capacity. It also has an impact on shape and general form.

    * The frontal and parietal bones recede,
    * The occipital bone is flattened,
    * The face is larger compared to the rest of the head.

    Do any of those symptoms appear in the Flores specimens?

    If not, the argument that they are microcephalic is fundamentally flawed. As Terry stated, island species often are smaller than their mainland equivalent. That is an established biological fact. So size alone is not sufficient evidence to state that the Flores specimens are pathological rather than merely a smaller sub-species.

    I would agree with you that if microcephaly is going to be convincingly mooted as an option, then it needs to be investigated properly. All elements of the skeleton – cranial and post-cranial – should have a detailed examination for all of the signs and symptoms of the condition, ideally by someone who is an expert in recognising the condition if it is there.

  5. We did not ignore the pathology issue in our paper on the Flores material. Kambiz, if you read the paper closely, we did include an achondroplastic dwarf in the study, and although its capitate was missing, the rest of the wrist looked like a small version of the nonpathological modern human condition and plotted accordingly in our morphometric analysis. Postcranial elements of microcephalic individuals are difficult to come by. Most museums only have the skulls; otherwise, we would have happily included one in the analysis. To find carpal elements will probably require quite a search through museum collections, so if you happen to know anyone who has a complete skeleton of a microcephalic, please let me know. In the absence of available microcephalic postcrania, we did our best to address the pathology issue from a theoretical standpoint. Given the early ontogenesis of carpal shape, it is highly unlikely that pathology could mimic the primitive condition of the carpals exhibited by LB1, since most candidate pathologies tend to act later on in development. The carpals look like those of an ape, but are otherwise well-formed.

  6. I misstated; our analysis in the Flores wrist paper included a pituitary dwarf, not an achondroplastic dwarf. Please feel free to edit my last comment during moderation or to post this as a separate comment. Thanks!

  7. Whoa, hello Caley. It is not often that a second author of such a high impact study comes around this neck of the woods. Thanks for commenting and correcting my errors. I appreciate it a lot.

    I did not catch the reference to USNM314306 until now. And yes, I see your point about the lack of microcephalic postcranial elements… hell there aren’t many microcephalic skulls.

    Thanks again,

    Kambiz

  8. Endemic cretinism, because of a lack of iodine, is another idea. I believe this does affect some postcranial parts. Don’t think it’s argued that these are necessarily H. sapiens afflicted with cretinism, perhaps could be erectus.
    However, I’ve always supported that the ‘hobbit’ remains represent a newly discovered species. It seems very plausible to me.

  9. Greetings,

    I believe this diagram below:

    http://www.newscientist.com/article/dn12667-hobbit-wrist-bones-suggests-a-distinct-species.html

    demonstrates much more clearly that the ‘hobbit’ wasn’t a modern human. In fact, the ‘danger’ is now in the other direction…if the wrist bones are essentially the same as that of a chimp, does this creature belong in the genus homo?

    Actually, I currently favor the idea that this was a last remaining descendant of the homo erectus population in Indonesia (note that recent research has found that Javan homo erectus still existed just 50,000 years ago) and that it gradually got smaller due to ‘island dwarfism.’ Still to be determined: did this creature go extinct 12,000 years ago, with a major volcanic eruption?

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  11. Now guys, here you overlook one important aspect: “Frequencies for microcephaly may be up to 1 in 2,000 births in isolated (inbred) populations.”

    The findings reported a complete skull, a second complete jaw, and fragments of other jaw/skull pieces. The second jaw piece matched EXACTLY with the previous one, and obviously it is doubtful that a second case of microcephaly would happen.

    Besides, the other pieces match along with the first two, thus proving that it cannot be microcephaly.

  12. This is an old post so I’m not sure if anyone is still following it or commenting on it. I’ve recently been doing a lot of study on Homo floresiensis and too have gone back and forth on the issue. But one thing does bother me about this that I rarely see mentioned.

    Microcephaly appears to be fairly rare as someone mentioned, appearing in 1 in 2000 births in isolated inbred populations. From what I’ve read, Microcephaly would mean poor brain function and the potential for other abnormalities and complications. It also leads to shortened life expectancies. With homo floresiensis being estimated to have been 25-30 years old, it would seem to be rare in itself that this individual could have survived that long in a primitive culture with such a disability.

    This isn’t to make a scientific judgment either way. I’m just stating that the probability of finding an individual with microcephaly who has lived that long at that time would seem to be something that has staggering odds. I’ve never seen this brought up in arguments.

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