I, or someone, have drawn a brown, orange, and blue Gwenhidwy

You’re probably thinking, “I thought zacharoo was dead,” because I’ve been completely MIA for the past few weeks. My apologies, but I was trying to wrap up this past semester, the terminus of my first year in grad school. And I must say I think I did a pretty good job, not to toot my own horn. This is as good a time as any to ask, “What the eff have I learned this year?”

1. Milford is awesome. Probably the past few decades have shown this, but I’ve only known the guy for less than a year. Given my more ‘arts’ educational background, Milford (and the Big Chief and the rest of the bios) have taught me how to do ‘science,’ formulating and testing a hypothesis. Though I’m certainly no Chung-I Wu, my mentors and colleagues have certainly gotten me started. Also, I was a bit unhappy with Milford last semester for pushing me and my peers to take a heavy course load. But I must say it was worth it, I’ve learned a lot this past year, and if I’d taken another (i.e. the non-bio) way I would not have learned nearly as much. He can also improvise a wicked country-twangy song (“I wish I grew up on a pig farm”). Great advisor, great man.

2. Steer clear of the hobbit. That situation is messier than the van-ride back from DC. I talked about LB 1 (the hobbit skull) in a few posts earlier this year. It’s clearly not a cretin, and at the AAPA meetings in Columbus a few weeks ago, Dean Falk defensively countered the Laron Syndrome hypothesis. Bill Jungers reported at the meetings that the foot of LB 1 was not that of a runner (I forget the specifics, but it was missing one or both of the plantar arches). It’s overall cranial shape based on various measurements show it has striking affinity with Homo habilis (in a broad sense) <!–[if supportFields]> ADDIN EN.CITE Gordon200810310317Gordon, Adam D.Nevell, LisaWood, BernardThe Homo floresiensis cranium (LB1): Size, scaling, and early Homo affinitiesProceedings of the National Academy of SciencesProc Nat Acad SciProc Nat Acad Sci07100411052008March 20, 2008http://www.pnas.org/cgi/content/abstract/0710041105v1 10.1073/pnas.0710041105<![endif]–>(Gordon et al. 2008)<!–[if supportFields]><![endif]–>. Chief, her husband Adam, Pappano, and I looked at UM’s collection of modern human ‘microcephalics’ (there are myriad ways to be microcephalic), and found that LB 1 is still more similar to the habilines (cf. Gordon et al 2008). This really suggests to me that maybe some early Homo or Australopithecus species made it out of Africa to Flores early in human prehistory; however, I don’t think we can say yet whether it’s a real case of insular dwarfing in a hominin or pathology or what. Still very messy.

3. Molding and casting is neat but difficult. One of the projects Milford got me started on a cranial reconstruction. Sounded simple enough at first, but it has required me to make molds and casts of the individual cranial bones: the two temporals, occipital and the paired parietals were not too difficult, but the face is really giving me grief. It was also difficult fitting my busy schedule to Bill Sanders’s lab schedule. So, long story short, I didn’t finish the project (should be done before June . . .), but Bill has taught me a ton about molding and casting, as well as proffered his wisdom. It has also reinforced my desire to be a paleontologist. Cool beans.

4. Genetics sucks. For decades now, paleoanthropology has come to be not just about fossils, but also about molecules. Today, genetic studies are incredibly influential in studies of human evolution, i.e. supporting models of migration and introgression. But I took a course this past semester in the department of Ecology and Evolutionary Biology, and it seems to me that molecules are not really any less unequivocal than fossils. Really genetics is all comparing predictions of models with various parameters (i.e. effective population size, population expansion, etc.) with actual empirical data, and it’s all about probability. So you can say something like, “There is a high probability of seeing this type of data given that type of hypothesis/model.” But different sometimes data have the same probability given different parameters. So genetics can tell a lot, but you have to take what they say with a gram of coke, I mean granary of salt. And all the nucleotides in the world probably won’t help resolve robust australopithecine phylogeny.

Now I’m tired, so I’ll stop there for now. I’ll post more pearls (of wisdom) I learned this semester as I recall them. So that’s where I’ve been o’er the past few somethings. Weeks. Oh, and I just received a possible job offer working with crash-test dummies (or something, I’m not exactly sure) with the UM Transportation Research Institute, hopefully that works out.

Reference

<!–[if supportFields]> ADDIN EN.REFLIST <![endif]–>Gordon AD, Nevell L, and Wood B. 2008. The Homo floresiensis cranium (LB1): Size, scaling, and early Homo affinities. Proceedings of the National Academy of Sciences:0710041105.

The Little Hominin That Could (Fuel Publications)

Two and a half months into 2008 and we already have three (if not more) papers out about (or with bearing on) the diminutive Flores hominin material. Indeed, interested paleoanthropologists are like the “first family” at AL 333, and the papers an interesting catastrophic event that is burying us all (not that they’re terribly bad, or anything).

As mentioned in an earlier post (“Cretins and Omomyids”), the past four years have borne witness to a huge debate on whether the ‘Homo floresiensis‘ is a new species of insular dwarfed hominin, pathological early human or what. There is no doubt about the fact that the material from Liang Bua cave, dating to as recent as 12 ka, is small. What has been most hotly debated is the etiology of the unique features of the LB-1 skull, such as (From Brown et al. 2004):

  • Cranial capacity estimated ~400 cc
  • Reduced parietal lobe development in the brain (relative to H. sapiens)
  • Long, low cranial vault
  • Maximum cranial breadth just above the mastoids
  • Prominent nasal pillars
  • Mesially rotated mandibular P4s
  • Posteriorly inclined mandibular symphysis (i.e. no chin)

Arguably these traits distinguish LB1 from modern humans (although one of my mandibular premolars is fairly mesially rotated), and more closely aligns it with earlier Homo taxa, e.g. H. habilis/erectus. Last year, Hershkovitz et al. made a pretty strong case for many of these ‘distinguishing’ characters being the result of Laron syndrome.

The first floresiensis-related paper this year was Obendorf et al.’s diagnosis of myxoedematous cretinism. According to them, thyroid malfunction resulted in the anamolous Liang Bua morphology. Their basis for this diagnosis was what they perceived to be an enlarged pituitary fossa, based on a picture of a CT scan. Though interesting, this hypothesis was nevertheless blown out of the water, as many parties–many of whom have seen the actual specimen–denied existence of an enlarged pituitary fossa. Bummer there.

A few days later, Berger et al. reported on diminutive humans (dating to 3-0.9 ka)from caves on the island of Palau. Authors noted some similarities to the Liang Bua material. They suggested that, since their material is undoubtedly human, but similarly tiny like floresiensis, many of the unique features of floresiensis might really be a function of their diminutive size, and that new species designation might not be appropriate. Of course, most of the LB 1 anomalies are cranial, and Palau crania are not yet observable, so Palau, at the moment, has little bearing on Liang Bua (viz. LB 1 and 6).

Finally, Gordon et al. today published a paper in which they used craniometric morphology of LB 1 to establish its taxonomic affinities. Their analysis shows that LB 1 falls outside their human sample, and clusters well with H. erectus, in a broad sense, and to a lesser extent with H. habilis. Thus, contra those who posit that LB 1 is human, but unique because of pathology or pleiotropic effects of small size, Gordon et al. support the idea that LB 1 (and therefore, all diminutive Liang Bua hominins) represents a new species, derived from H. erectus or habilis (cf. African or Dmanisi erectines). Their compartive sample included 2500 modern human crania from all over the globe and 30 hominin crania.

I suppose that I have to take issue with the sample. Comparing LB 1 to modern human crania from all over the globe is a bit like comparing a 15 ka Javanese apple to a modern, international fruit basket (I admit I’m embellishing). On the other hand, comparing it to a wide diversity of human crania might be generous, as it increases the range of variation, making it easier for LB 1 to fit in. But they did not address the issue of pathology very well. They write:

With regard to microcephaly, it should be noted that in the shape analysis performed here, LB1 cranial shape is shown to differ significantly from the modern human comparative sample (and from fossil H. sapiens and Neanderthals) and to be very close in morphological space to non-Asian H. erectus specimens (D2700 and KNM-ER 3733). And H. habilis specimens (KNM-ER 1813 and OH 24). LB1 and the non-Asian H. erectus specimens are much closer than the average pairwise distance between modern human crania, and standardized residuals of LB1 from the estimated non-Asian H. erectus and H. habilis scaling relationshps average 1.38 and 1.21 standard deviations away from expected shape, respectively . . . well within the range of population-level variation (Table 1). Thus, if microcephaly is responsible for the extremely small size of the LB1 cranium, of all possible ways that microcephaly could cause LB1 cranial shape to differ from that modern humans and for these six variables, it happens to differ in the same way that earlier Homo species differ from modern humans [p. 4654].

Ok, so here they sort of test the hypothesis that LB 1 is craniometrically like a microcephalic by comparing it to a large sample of non-microcephalics–now that’s comparing ancient apples to a Harry and David exotic fruit basket! To my knowledge, Argue et al. (2006) are the only ones to compare craniometrics of Liang Bua to any microcephalics. Their findings (see their Figs. 3 and 4) show that, as in the Gordon et al. study, LB 1 is most close to ER 3733 and OH 24. But, this study looks at only two microcephalics (though they compare LB 1 to these in separate analyses…), and these two individuals are on the extreme margins of a wide range of human variation. Moreover, there are myriad ways to be microcephalic, and it is unclear how different ways might affect craniometric variation.

That Gordon et al. and Argue et al. agree that LB 1 is craniometrically very similar to ER 3733 and OH 24 might not be insignificant. But Gordon et al. make the assumption that modern human microcephalics are craniometrically no different from non-pathological humans. While the Argue study suggests microcephalics might not be too different, they do show they are nonetheless on the outskirts of human variation (when also compared to fossil hominins…); moreover their microcephalic sample is very small. In order for Gordon et al. to reject microcephaly, they need to satisfactorily establish that microcephalics are not too different from humans cranimetrically. And that requires a larger sample of microcephalics. Hey, there’s a handful of microcephalic skulls (get it–“handful,” cuz they’re micro…) in my lab, maybe I’ll undertake this endeavor, after I get done with my billion other projects….

Anyway, apparently Hershkovitz et al. didn’t officially settle the Liang Bua issue. It’ll be interesting to see what Falk et al. bring to the table in Columbus in a few weeks. A never-ending saga . . .
References
Argue D, Donlon D, Groves C, and Wright R. 2006. Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo? J Hum Evol 51: 360-374.

Berger L, Churchill S, de Klerk B, Quinn R. 2008. Small-bodied humans from Palau, Micronesia. PLoS ONE 3: e1780

Brown P, Sutikna T, Morwood M, Soejono R, Jatmiko, Wayhu Saptomo E, Awe Due R. 2004. A new small-bodied hominin from the Late Pleistocene of Flores, Indonesia. Nature 431: 1055-1061.

Gordon A, Nevell L, Wood B. 2008. The Homo floresiensis cranium (LB1): Size, scaling and early Homo affinities. Proc Nat Acad Sci 105: 4650-4655.

Hershkovitz I, Kornreich L, Laron Z. 2007. Comparative skeletal features between Homo floresiensis and patients with primary growth hormone insensitivity (Laron Syndrome). Am J Phys Anthropol 134: 198-208.

Obendorf PJ, Oxnard CE and Kefford BJ, in press. Are the small human-like found on Flores human endemic cretins? Proc R Soc B xx: 1-10.

Cretins and Omomyids

What’s new in the world of Paleoanthropology?

The first bit of news is older than dirt: Christopher Beard reports in the 11 March issue of PNAS on new evidence of the earliest primates in North America around the time of the Paleocene, some 60-55 Ma. Fossil teeth discovered in Mississippi have been allocated to a new species, Teilhardina magnoliana, arguably the most primitive Teilhardina in North America or Europe. Beard argues this suggests that, contrary to current understanding of euprimate dispersal, early omomyids colonized North America around the Paleocene-Eocene Thermal Maximum via a Bering Strait land bridge. Possibly, these early critters thence colonized Europe. Pretty neat stuff: early primate forebears disperse from Asia to N. America, and some 55 Ma later modern humans follow their tiny footsteps. I don’t know very much about primate origins (my interests like some 50 Ma after this event), but it’s always nice to have a reason to say “omomyid” or “omomyiform.”

Next, one of the most sensational paleoanthropological news bits, the famed hobbit, is back in the spotlight, in a paper in the Proceedings of the Royal Academy B. Recall that when the Flores hominin material was first reported about five years ago, it was argued to be a new species of an insular-dwarfed erectus-like hominin: Homo floresiensis. Others later argued that the Liang Bua material was pathological (i.e. microcephalic dwarf) H. sapiens. Most recently, Hershkovitz et al. made a pretty convincing case that the LB 1 was a modern human with Laron Syndrome, a pituitary disease. Their case is pretty strong, but the most troubling evidence, in my mind, against a pathological human is the fact that the diminutive Liang Bua specimens are very small and span a period of thousands of years. I look forward to Falk et al.’s presentation at the AAPAs in April (“LB1 did not have Laron Syndrome”).

But the new Obendorf et al. paper gives the hobbit a new diagnosis: “myxoedematous cretinism.” Thus, the diminutive stature and small brain of LB1, Obendorf and team hypothesize, is due to a non-functioning thyroid. Support for their hypothesis comes from, among other things, the enlarged pituitary fossa of the LB1 sphenoid and the morphology of the LB1 trapezoid. I must admit now that I have not yet read the entire paper (I have to teach in 10 minutes) but the paper looks interesting, and I am interested in how they propose to explain how only the “cretins” were preserved in Liang Bua cave, while non-pathological humans were not. The paper also reminds me of Dobson’s (1998) paper that suggested that the thyroid and iodine deficiency were responsible for the anatomical differences between humans (as we generally know them today) and neandertals. I guess the evolutionary significance of the thyroid is really beginning to be appreciated by anthropologists…

Given this new diagnosis for LB1 and others, what might be interesting is a Bayesian approach to testing these hypotheses. Which hypothesis (diagnosis) is most likely given the data–new species, microcephalic or microcephalic dwarf H. sapiens, human with Laron Syndrome, or human cretin? Or, under which hypothesis(-es) are the observed data the most likely? The new diagnosis for the Liang Bua material is interesting and certainly provides good research questions. But, as is usually the case with fossil hominins, what would be really nice are more specimens against which to test our hypotheses.

References
Beard C. 2008. The oldest North American primate and mammalian biogeography during the Paleocene-Eocene Thermal Maximum. Proc Nat Acad Sci 105: 3815-3818.

Obendorf PJ, Oxnard CE and Kefford BJ, in press. Are the small human-like found on Flores human endemic cretins? Proc R Soc B xx: 1-10.