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Wednesday, December 24, 2008

More LB1 stuffs, but no real news

New analyses of the Flores “hobbit” material have been published recently, including a geometric morphometric (GM) study of the LB1 cranium (Baab and McNulty, in press). Readers will recall that this particular small-brained specimen has fueled the controversy over whether the Flores material is a unique, small-bodied hominin species, or whether this and other specimens were pathological (humans). At this stage in the game, I still do not know what we can say exactly is going on until we get more fossils. Admittedly, I haven’t yet read the recent analyses of the postcranial material. Maybe they will change my mind. So, I’d like to keep this more descriptive and comparative, than speculative on phylogeny versus pathology. Some neat things from the study:

Coordinates of landmarks were recorded off a “stereolithographic model” of LB1. This is a neat technology in which a plastic 3D model is ‘printed out’ based on data from a CT scan. While this might not give the same resolution as the real thing (or a good cast of the real thing), it’s a great way to make physical models of delicate fossils. Additionally, measuring/collecting landmark data from fossils can always potentially damage specimens, and stereolithography is a way to circumvent this problem. However, I don’t know that it would have been any more difficult to digitize landmarks from the actual CT scan (i.e. with a computer software package), and it almost certainly would have been cheaper. Oh well, smoke them if you’ve got them, right?

The study used GM to compare the shape of LB1 cranium to the shapes of apes, fossil hominins and modern humans. I like that the study included the analysis in Procrustes shape space (with nuances of location, rotation and scaling omitted) and in form space (omits only location and rotation, leaving size/scaling in the analysis). By examining the specimens in form space, the authors were able to study the relationship between shape and size, i.e. the effects of allometry: what cranial shape would “an LB 1-sized individual” of each taxon have? The results of the form space analyses are kind of neat, although I can’t interpret them too readily since I’m not sure what exactly the first two PC scores indicate, other than size. In a nutshell, though, LB1 appears most similar to what would be expected of a small-bodied fossil Homo individual. Of course, this is nothing new: Gordon et al (2008) came to the same conclusion last year, but using inter-landmark distances as variables (as opposed to landmarks as variables). Additionally, last year we found that the microcephalics in our lab appear more similar in shape to modern than fossil humans (I wonder if we should have tried to publish that…).

The authors also examined asymmetry as a way to address the allegation of pathology in LB1 (left-right asymmetry is believed to be indicative of developmental disruptions arising from environmental or genetic stress). LB 1 is more asymmetrical than the human mean (but within the range of variation), and roughly in the middle of the range of variation for fossil hominins. This suggests to the authors that LB1 is not pathologically asymmetrical, and that asymmetry in the fossil is rather likely due to effects of fossilization. Unfortunately, however, the issue of pathology-related asymmetry is not wholly adequately addressed, so this result must be taken with a grain of salt (fluctuating asymmetry is generally believed to indicate developmental disruptions, and there are two other types of asymmetry that must be factored out…). It is at this point that some GM qualms I have come to the fore. Really there’s one issue specifically: homology and measurement error.

As mentioned above, GM statistically analyzes shapes using landmark coordinates as variables. Of course when comparing things, you want to make sure you’re actually comparing equivalent things (“homologous” structures). So on a cranium there are a few, which Bookstein identified as “Type I,” and are often the intersections of bony sutures, such as the point where your two nasal bones contact your frontal bone. But beyond that, many landmarks are extrema (“Types II-III), i.e. points of widest breadth, which are not necessarily (ever?) homologous structures. The trouble, then, is a large risk of comparing non-homologous structures, which can render biological analyses nearly meaningless. Additionally, many of these such points must be found fairly arbitrarily, which means that even if given landmarks are homologous (i.e. biologically meaningful), there is a good chance of measurement error confounding the study--this is especially true in fluctuating asymmetry studies.

Use of these Type II-III landmarks is not terrible, it’s just a reason to be wary. One must ask, based on how arbitrarily a landmark was found, and the likelihood of measurement error, how meaningful will the results be? One landmark that comes to mind from this study is alare, “the most lateral point on the margin of the nasal aperture.” How significant is ‘lateral-most’ as a criterion--is there something functionally important about this point, and is it very variable within a given taxon (I really do not know, but now I’m interested…)? Moreover, the margins of the nasal aperture (“nose hole”) are not always sharply delineated, but can be rounded, making the margin itself difficult to identify: for example, OH 5 has very rounded margins, but KNM-ER 406 seems to have sharp margins--both specimens are Australopithecus boisei. In this study, alare contributed second most to individual asymmetry in all taxa. Is this because of measurement error, or the fact that this is not a biologically significant point, or both/neither? Other fun landmarks include “malar root origin," and “Frontomalare temporale… The point where the frontozygomatic suture crosses the temporal line (or outer orbital rim)” (my emphasis). So throughout the study, you took either one intersection or the other?! When did you use which one, and why? Homology FAIL. Maybe I (or someone else) will come up with a new (hopefully better) way to study asymmetry… Now I’ve lost my train of thought.

References
Baab K and McNulty K. Size, shape and asymmetry in fossil hominins: The status of the LB1 cranium based on 3D morphometric analyses. J Hum Evol, in press.

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

Sunday, December 14, 2008

Wordle

This is cool: you can put in any words (I found it because another blogger wordled her dissertation), and it will make one of these word figure things. OR you can put in the URL for any website with an RSS feed, and it will create one for that text! Words that are used more often are larger, common words ("is" "and" "the") are ignored, and you can change the font/color scheme. Here's one for Lawn Chair Anthropology:


Here's a wordle for Clifford Jolly's article "The Seed-Eaters: A New Model of Hominid Differentiation Based on a Baboon Analogy":


This is fun!

Tuesday, December 9, 2008

Women in Science

Yes, surprise, another post by me (Caroline, NOT Big Chief, despite certain RSS feeds)!

Browsing around the interweb this evening, I came across a number of blogs by women scientists (both grad students and professors) that detail some of the issues that they face in their career of choice. The writers don't let on which "-ology" they study, or what university they are associated with. Now, with the exception of ones my advisor suggests to me (Hawks), or ones I find through links from Hawks, or ones my friends write, I don't really read academic blogs. So finding these was a wake-up call (to me) making me realize what Hawks meant when he posted his blogging philosophies a while back and mentioned the "to be anonymous or not" debate. It makes me wonder if these authors worry about not gaining tenure because of something they post in a blog, or if (despite my having skimmed the posts on their first pages) some of the blogs' content is not so academic after all, or if they use their blog to trash people in their profession... But, aside from these curiosities, I am mainly interested to learn what women in scientific academia deal with on a daily basis. In case any of you are also interested in such blogs, here are the ones I found:

Friday, December 5, 2008

Whopper Virgins and Oldest Human Tools

John Hawks added a number of new posts to his blog recently, some of which spur me to typing. 

First, Whopper Virgins. This newest Burger King ad campaign has people from remote areas of the world (sans burger joints) decide which burger is best: Whopper or Big Macs. Hawks links to Althouse's blog, where she describes numerous problems with these commercials. One she misses though, is how this is also a problem for the Burger King. Since the folks in these regions HAVEN'T EATEN BURGERS before, they might not judge them on the same taste preferences that burger epicures (like most of BK's clientele). So if they choose the Whopper over the Big Mac, that might not be something the BK Lounge (anybody?) should be advertising! I also agree with most of the other problems listed in Althouse's blog post, and overall think this is a poorly thought out idea on BK's part.

Second, "Humans 80,000 Years Older Than Previously Thought?" Nat Geo article: The evidence? "sophisticated stone tools found in Ethiopia" date them to 276,000 years old; while the oldest Homo sapien is 195,000 years old (referring to Omo skulls). OK, I don't know much about the Omo skulls, or how they dated the stone tools, but even given that evidence, this seems like the wrong conclusion. BECAUSE THEY ASSUME ONLY MODERN HUMANS COULD HAVE MADE THESE TOOLS!!! Seriously? The only evidence they're giving for super old humans is some tools they don't think another hominid could have made??